- Email: [email protected]
Galton, Francis
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from turnover of galactose-containing complex glycoconjugates. Short-term 2-h oxidation of isotopic galactose to CO2 is very slow in most patients, but 24-h oxidative capacity is similar to that measured in normal patients after 5 h. The oxidative pathways involved have not been completely defined. This capacity to oxidize the sugar plus the urinary metabolite excretion maintain the patient in a steady-state with plasma galactose levels in the low micromolar range. The human galactose-1-phosphate uridyltransferase gene of 4 kb has been cloned and sequenced and consists of 11 introns and exons on chromosome 9. The cDNA codes for a 374 amino acid protein, with about 49% conservation between human and Escherichia coli enzymes. The active enzyme is a dimer with a molecular mass of 96 kDa. There are over 100 mutations known to occur in galactosemic patients. Most are missense mutations with a single base change, but stop mutations, splice site changes, frameshifts, and large deletions are found. The most common mutation, accounting for over 60% of mutant alleles, is Q188R, in which arginine is substituted for glutamine in the highly conserved region of exon 6. About 45% of patients are homozygous for Q188R. A number of Q188R alleles are compounded with other mutations. In African American and South African black galactosemics the prevalent mutation is S135L. The Q188R mutant is believed to be devoid of enzyme activity, while the S135L mutation results in residual liver enzyme activity. Heterodimer formation may be a significant determinant of enzyme activity. The N314D mutation with an asparagine to aspartic change is prevalent and the basis of the Duarte variant. It results in diminished but not absent erythrocyte enzyme activity and is itself benign. There appears to be no clear genotype±phenotype correlation. However, the ability to oxidize administered 1-13C galactose to 13CO2 of less then 2% in 2 h appears to indicate a more severe disorder as observed in many Q188R homozygotes than that present in compound heterozygotes. Neither the pathobiochemical basis of galactose toxicity in the newborn period, nor the late onset long-term diet-independent complications are known. Accumulation of galactose-1-phosphate and galactitol are believed to be responsible, but the mechanism of multiorgan involvement is unclear. Cataract formation is associated with galactitol accumulation. A knockout mouse with absent transferase activity shows no manifestations of the human phenotype, suggesting that absence of transferase is necessary but not sufficient to cause disease. This points to epigenetic factors and abnormal alternative pathway metabolites as the possible basis of the human disease.
The only known treatment of galactosemia has been restriction of lactose and other galactose-containing foods. Although the postnatal toxicity is alleviated, the long-term complications have not been averted. Speech therapy, special schooling, and hormonal therapy of ovarian failure are indicated and may be helpful. The disorder remains an enigma requiring the search for new therapeutic strategies. See also: Lactose
Galton, Francis R Olby Copyright ß 2001 Academic Press doi: 10.1006/rwgn.2001.0490
The Victorian intellectual Francis Galton (1822±1911) was one of the chief founders of the science of biometry, or the statistical and quantitative study of living things. He described its chief objective to be ``to afford material that shall be exact enough for the discovery of incipient stages in evolution,'' stages that are ``too small to be otherwise apparent.'' His goal was to establish the foundations upon which to base a policy to control and direct the future of mankind. In 1883 he coined the word `eugenics' for the science of improving stock, a term, he remarked, that is not confined to questions of judicious mating, but which especially in the case of man, takes cognizance of all influences that tend in however remote a degree to give to the more suitable races or strains of blood a better chance of prevailing speedily over the less suitable than they otherwise would have.
Galton was particularly concerned to show that the behavioral as well as the physical traits of mankind are inherited, that what is acquired in life cannot be passed to the offspring, and that nature (that which is inherited) has much more influence on the individual than has nurture (that which is gained from experience and education). He was, in other words, an `hereditarian.' But he did not simply make hereditarian claims. He developed the statistical techniques of regression and correlation to analyze the biometric data he collected from sampling human populations. His passion for quantitative treatment he also applied to establish weather patterns, to test the effectiveness of prayer, and to explore sensory perceptions, imagery, and memory. The zoologist Raphael Weldon and the mathematician Karl Pearson became devoted followers of
Galton, Francis 743 Galton. From the 1890s they vigorously developed the science of biometry, and in the early years of the twentieth century they opposed the newly rediscovered science of Mendelian heredity. Nearly two decades passed before biometry and Mendelism were effectively united to form what we call population genetics. Meanwhile Galton's science of eugenics passed through phases of popular approval and disapproval. The intensive study of the chemical sequence of the genetic material of our genes that has been ongoing since the 1980s has once more brought the subject of eugenics to popular attention. Could new and powerful techniques now make possible a kind of eugenics ``by the backdoor''? Not, in other words, public legislation enforcing eugenic policies, but covert pressures of the market through discrimination, and limited access to resources.
Francis Galton's Life Galton came of a wealthy and well-connected family, his mother being the daughter of Charles Darwin's grandfather, Dr Erasmus Darwin. As a boy and the youngest in the family, much affection was bestowed upon Francis, especially by his three sisters. AdeÁle, the youngest, acted as his tutor, and those around him soon considered him an infant prodigy. However, formal education, neither in France where he was sent at the age of eight, nor in England from the age of 14, proved to be to his liking. At 16 he began to study medicine, but two years later he turned to mathematics and moved to Cambridge. Four years later he gained a BA without honors and prepared to return to his medical studies. Then his father died, and he came into an inheritance that permitted him to forget medicine and indulge in his love of exploration. The resourceful and courageous young Galton traveled through Egypt, Syria, and South West Africa, where he covered some 1700 miles of uncharted country and came to know the Damara, Namaqua, and Ovampo tribes. He was struck by their distinctive behavioral and physical characteristics, and those of their domesticated animals. On his return to England in 1852 the Royal Geographical Society awarded him their gold medal for his achievement. During the 1850s he worked to promote geographical exploration, published his guide The Art of Travel (1855), introduced weather maps, discovered anticyclones, and worked for the British Association for the Advancement of Science. When in 1859 his cousin Charles Darwin published his book On the Origin of Species, Francis read it and was greatly impressed. If all life is the product of evolution, we should be able, given sufficient knowledge, to control our own evolution ± our future. But, like his cousin, he realized there
was a weak spot in the theory, the lack of sound knowledge of the nature of heredity. Accordingly, he turned in the 1860s to address this subject. Between 1865 and 1889 he worked often obsessively on gathering material. Publications on the subject flowed from his pen, the most important being his two books: Hereditary Genius (1869) and Natural Inheritance (1889). He lived on to 1911 ± long enough to seize the opportunity that the changing political climate of the new century afforded him to publicly appeal for the establishment and support of the science he called eugenics.
Human Heredity Conceptual
During the nineteenth century Herbert Spencer and Francis Galton gave up the term `inheritance' and following the French they substituted the term `heredity' (heÂreÂditeÂ). This signaled Galton's conception of heredity as based upon the continuity from generation to generation through an unbroken line not of persons but of the elements in the fertilized eggs from which they came. The term `inheritance' suggested the legal concept of the transmission of a person's estate to his descendants. Here the link is between the visible characteristics of the grown person (the parent) and the corresponding features of the offspring. But heredity is often indirect. The offspring bear similarities to many ancestors, not just to the parents. Moreover Galton was convinced that nothing we acquire in our organic constitution can thus be passed on. If we behave more virtuously, will our children do likewise? Do the sons of old soldiers, he asked in 1865, learn their drill more quickly than others, or the sons of fishermen escape sea-sickness? And if acquired characters are inherited, why have the many tribes of American Indians, though scattered over the vast range of different climates and situations of the Americas, remained much the same? Yet, if heredity is so unyielding, why is it that a father's characters are sometimes revealed in the son, sometimes in the daughter, or the child may bear the character seen only in a grandparent or more distant ancestor? How can so hard a process be so fickle? Galton saw that the answer lay in the statistical study of large numbers of ancestors and descendants, and in making an analysis of their statistical relations one to another. This is the heart of his project for what was later to be called biometry.
Observational
First he wanted to gather evidence that behavioral as well as physical characters are inherited. He chose to study what he called `genius,' or as he defined it, an
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ability that is ``exceptionally high, and at the same time inborn.'' It excludes any ability that can be attributed to the effects of education, but it includes an energetic disposition. Brilliance without application, persistance, and stamina, is of little use. Then he made the questionable assumption that ability correlates with eminence in public and professional life. Noting that great ability seemed to cling, as it were, to particular families like his cousin's, the Darwins, or the Bachs with its musicians and the Bernoullis with its mathematicians, he turned to the legal profession and extracted the names of 109 judges sufficiently eminent to be mentioned in Foss's Lives of the Judges (1865). Then he tracked the 85 families involved to establish how many relatives of these judges also achieved eminence in the legal or other professions. He found that one in every nine of these judges was either father, son, or brother to another judge, not to mention the relations of judges that attained higher legal office. He set out his results in tabular form (Table 1). The table illustrates how fewer and fewer relations of the most gifted member of a family attain to eminence the more distant is their kinship to that member. The percentages, wrote Galton, ``are quartered at each successive remove.'' He concluded that the data show ``in the most unmistakable manner the enormous odds that a near kinsman has over one that is remote, in the chance of inheriting ability.'' To consolidate this claim he turned to another eight professions, and to oarsmen and wrestlers. Most of the data were supportive of his claim, though he noted that some sons of very pious parents occasionally turn out extremely badly!
Methods in Population Studies Pedigrees
To the objection that Galton was ignoring the effects of nepotism, and the advantages of privileged upbringing and expensive education, he replied with the names of great men who, despite their lowly origin, had become eminent. This criticism, of course, struck at Galton's assumption that public eminence is a measure of native ability. He was aware of another problem, i.e., the underrepresentation of family data. This is the Achilles heel of the pedigree method, i.e., the use of family pedigrees for genetic data collection. Have some of the `failures' in life been left out? Are more representatives of the male kin included than those of the female? And how does one assess the contribution to ability coming from the females in the line using professional achievement at a time when the professions studied by Galton were not open to them? By the 1890s whole-population studies were being undertaken in Germany to escape such criticisms in the debate over the supposed inheritance of tuberculosis,
Table 1 The judges from 1660 to 1865. (From data in Galton (1889) Ancestral Inheritance.) ½ Great-grandfathers
7½ Grandfathers
½ Great-uncles
4½ Uncles
26 FATHERS
The most eminent members of 23 BROTHERS 1½ First cousins 100 distinguished families
36 SONS
4¾ Nephews
9½ Grandsons
2 Great-nephews
1½ Great-Grandsons
and in the 1870s Galton developed his famous method of twin studies in his effort to gather reliable evidence concerning the relative power of heredity and environment upon the shaping of the offspring. This has become one of the classic approaches whenever dealing with human traits, since the experimental approach is excluded.
Twin Studies
For his study of what he called ``The history of twins'' Galton used the questionnaire method. Darwin had circulated a questionnaire in his study of heredity and variation in the 1830s, and Galton had followed his example in his investigation into the upbringing and personal characteristics of Fellows of the Royal Society. His appeal for information about twins resulted in 35 adequately answered responses from parents of `closely similar' twins, and 20 from parents of `exceedingly unlike' twins. These allowed him to distinguish between what we call identical and non-identical twins. From this comparison of the two groups he concluded that ``nature prevails enormously over nurture when the differences of nurture do not exceed what is commonly to be found among persons of the same rank of society and in the same country.'' This was a wise qualification because he did not have data on twins reared apart either in identical or nonidentical environments. Subsequent researches by Galton's successors did extend the data collection in this way, but it is questionable how different were the environments of the separate homes in which the two members of each pair of twins grew up. In the 1970s the most extensive collection of twin data, that of the British psychologist, the late Sir Cyril Burt, was exposed as fraudulent. On a subject as politically sensitive as the heredity±environment equation, this
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Regression
Another method of central importance in the study of populations is that of the statistical distribution of traits. Galton was aware of the curve of `normal' distribution, also known as the Gaussian or error curve after the mathematician Gauss who applied it to the study of errors in astronomical measurement. Following Gauss, the Belgian Adolph Quetelet found that the measurement of the chests of 5738 Scottish soldiers and the stature of 100 000 French conscripts, when compared with the expectation from Gaussian curves, showed a ``marvelous concordance.'' The graph is bell-shaped, its top or plateau representing the median of the data (Figure 1), the median being that value which divides the data on either side equally and symmetrically. As an error curve the sides of the bell represent the `population' of error measurements, and the top itself is hopefully the `true' measurement. As a representation of the distribution of the soldiers' heights, Quetelet envisioned the top as marking the height of the `average man.' Those taller or shorter than this measure were `errors' as it were in attempts to copy the ideal of the race. The fact that these data fitted the error curve demonstrated, in his view, that they were homogeneous. Galton focused his attention less on the homogeneity of the population than on its variability. How, in spite of variability, did its median remain the same in successive generations, for of this he was already convinced? Therefore, he wanted to dissect the curve into its parts and follow the progeny of those parts. So he devised an exploratory study in which he got his friends to help by asking them to grow sets of sweet pea seeds (Lathyrus odoratus), which he had divided into seven classes by weight. They returned the crop to him and he was then able to plot the progeny seed weights against the weights of their respective parents. The result revealed the presence of a tendency of the progeny of heavy seeds to be lighter than their parents and those of lighter seeds to be heavier. There was a `reversion' toward the ancestral mean. Since the aggregate mean remained the same and because his helpers all lived in different parts of the British Isles he was confident that the data did not reflect the effects of environment. This tendency to counteract the extremes of individual variation by `shrinking' the excesses whether dwarfs or gaints in their progeny he called `reversion,' and later more wisely, `regression,' since reversion was the term already in use to refer to the return of the progeny of hybrids to their originating
1200 Number of soldiers
revelation had a damaging impact upon the field, but careful twin studies continue, particularly as a tool in the study of hereditary predispositions to diseases, including mental illnesses.
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Figure 1 Graph of the distribution of chest circumferences of 5732 Scottish militia men. The figure approximates to the bell-shaped curve of a `normal distribution.' (Redrawn from data in Quetelet (1817) Edinburgh Medical and Surgical Journal: 260±264.) species. Now he could understand why variability does not change the median or `center of gravity' of the population. Having established in a rough manner evidence for this regression in plants, Galton cast around for data on human characteristics, but in vain. However, when he advertized prizes of £500 for those who best filled in the elaborate set of questions that he prepared concerning them, their grandparents, parents, sisters, brothers, children, and other relatives, he was rewarded with a good response. These family records included stature of family members, so he was able to plot the statures of parents against offspring from which he calculated the regression (Figure 2). He expressed what he called the `coefficient of regression' as the ratio between the deviation of the offspring and that of the mid-parents from the population mean. This is measured on the graph by the distances AB and AC or EF and EG. Since the data fall approximately on a straight line, the ratio is constant throughout its length, giving a coefficient of regression of two-thirds. Now he had measured a statistical relation between two generations.
Correlation
Initially he considered regression in one direction only, but later realized that the regression of the parent on the child is the reciprocal of the child on the parent. Then in 1885 he hit upon the concept of `correlation,' namely that where there is a relation between the variation of one entity and that of another, they can be considered causally related. This important conception was developed more fully later by Karl Pearson.
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of fractional inheritance, according to which the parents collectively contribute one-half, the grandparents one-quarter, and the great-grandparents one-eighth to the hereditary constitution of the offspring. These ancestral contributions exert their influence and tend to bring back the progeny of deviants toward the mean of the ancestral population as a whole.
Discontinuous Variation
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Figure 2 Graph of the relation between the midparental heights of parents and the mean height of their children. The diagonal line represent all points on the graph corresponding to hypothetical parents and their children where the means of the children's heights are identical with their parents. The steeper line is plotted from Galton's data. The ratios AB:AC or EF:EG give the coefficient of regression. (Redrawn from Galton (1869) Hereditary Genius: An Inquiry into its Laws and Consequences, pp. 83. London: Macmillan.)
Natural Selection Stabilizing Selection
Darwin had focused upon the slight individual differences that constitute the variation to be found among members of a family and of a species. ``They afford material,'' he said, ``for natural selection to accumulate, in the same manner as man can accumulate in any given direction individual differences in his domesticated productions.'' But Galton was convinced that natural selection cannot work effectively against heredity, and he considered that his work was showing heredity maintaining the racial mean. According to Galton, the mean is the adapted form and deviations from it will be less adapted to the conditions of life. Therefore, natural selection will be aiding heredity in preserving it. In other words, he granted natural selection its `stabilizing' role, but not its `creative role.' As the reason for this state of affairs he turned to the physiology of reproduction. The fertilized egg is composed of hereditary material from two parents, so that each time a new generation is produced there is a bringing together of two such materials. Inevitably the contributions of each parent and each ancestor will be diluted. So he accepted the long-held tradition
Having thus restricted the role of natural selection, he turned to `sports' of nature, those marked deviations that possess a stability shown by the absence of regression to the existing type among their progeny. These deviations create a new mean toward which any progeny will tend to regress instead of regressing toward the mean of the original population. Hence, he explained, these sports may give rise to a new race with but little help from natural selection. He was thus opposed to cousin Darwin who in his On the Origin of Species had stressed how unlikely it was that such sports could serve as the starting point for new species. Granted they were strongly inherited, but most sports were closer to monstrosities than to newly adapted forms. In any case, thought Darwin, their rarity would result in the dilution of their type in successive generations of breeding with other members of the species. Darwin proved to be largely right on his first objection, but wrong on his second. It should not be assumed that Galton's apostasy over natural selection was unusual for the nineteenth century. The consensus was in favor of evolution by descent, but not under the principal agency of natural selection. Therefore, it is ironic that those who most strongly supported the pre-eminence of natural selection considered themselves Galton's successors. Thus Karl Pearson and Raphael Weldon developed Galton's statistical techniques and corrected his errors. But when Weldon sought to demonstrate natural selection in its creative role, shifting the mean of a population, he only succeeded in demonstrating its stabilizing role. Pearson exposed some of the confusions in the several differing representations of the ancestral law offered by Galton. He corrected the figure of twothirds for the regression of offspring on parents, explained why regression was not the barrier to selection that Galton claimed, and explored the effects of `assortative' mating, i.e., the choice of mates based on similarities of ability and background, which promotes the shifting of the mean of the resulting offspring further and further away from that of the general population.
Finger Prints
The minute and distinctive patterns of ridges on the skin were used to make finger prints before Galton
Galton, Francis 747 took up the subject. But it was he who conducted a systematic study leading to his classification of the differing types and it was he who persuaded the police to adopt the practice of fingerprinting for personal identification of criminals. For Galton the subject had a compelling theoretical interest because the trait appeared to have no function such that natural selection could act upon it. Marriage selection does not depend on it; the different patterns are not confined to particular classes or races. Therefore, there is complete `promiscuity' with respect to this trait. Yet the varieties remain distinct. Here, then, we have a trait whose varieties do not blend and are not subject to selection. This, he believed, was an example of the existence and persistence of distinctive types independent of selection. Of course he could not really have known whether the trait was connected to some other trait that is subject to natural selection.
Eugenics Controlling our Evolution
The driving force behind Galton's extensive and longcontinued research was not just his curiosity, great as that was, but his vision of a future in which mankind would attain to greater energy and coadaptation. But he realized how easy it was to follow the wrong course. To accept the evolutionary process passively would be to surrender to ``blind and wasteful processes'' in which raw material is produced extravagantly and all that is superfluous is rejected ``through the blundering steps of trial and error.'' He favored the alternative that we should take control of our evolution, for it may be that we are the ``only executives on earth.'' Hence the importance of eugenics in providing the proper scientific basis for action. To support such work he settled an endowment on University College London so that in 1905 a Research Fellow in eugenics could be appointed. Further expansion led to the creationoftheEugenicsLaboratory.In1911,againthrough Galton's munificence, a chair of eugenics was established at the College, the first occupant being Pearson.
Victorian Attitudes
Galton's attitude to racial differences, to women, and to the indigent was typical of a wealthy Victorian. Mild of manner and gentle in his disposition, yet his attitude to the less fortunate was unquestionably harsh. Many at the time endorsed the policy of negative eugenics, i.e., to discourage the marriage and procreation of offspring by the exceptionally unfit, but Galton went further and wanted to favor those families that were ``exceptionally fit for citizenship.'' He argued that since there was substantial giving to the poor and destitute, could not support be forthcoming
to promote ``the natural gifts and the national efficiency of future generations''? His concern, like Pearson's, was over the differential between the reproductive rates of the upper middle and lower classes in favor of the latter.
Publicizing Eugenics
In 1904 the time was judged opportune for Galton to address the Sociological Society on eugenics. Here he argued for the maintenance of diversity, but ``each class or sect'' represented ``by its best specimens,'' and then to leave them to ``work out their common civilization in their own way.'' The best were the healthy, the energetic, the able, the manly (!), the courteous, but he advised leaving out the cranks and refusing the criminals. Eugenics should study the conditions that cause families to thrive and leave more descendants, so that the most useful members of society could be encouraged to adopt such conditions. The main task ahead was to establish eugenics as an academic question, then to bring about consideration of its practical development, and third to introduce eugenics ``into the national conscience, like a new religion.'' He ended by cautioning his audience against too much zeal which could lead to hasty action. A golden age is not round the corner, he warned. Such expectations would lead to discrediting of the science. In the event it took Hitler's treatment of the Jews in World War II to achieve that.
Conclusion Galton was the confident English gentleman, well aware of the superiority of his nation and his class, condescending to the former colonies, and dedicated to turning back the degeneration of his countrymen. But he disparaged the institution of the aristocracy, rejected the Christian religion, and considered many of our behavioral characteristics as outworn relics from a primitive stage in our social evolution. Although his mathematical skills were limited, his imagination, insight, and inventiveness were remarkable. Allied to his incessant curiosity, these talents made him one of the founders of the statistical revolution that occurred in his lifetime. His book Natural Inheritance (1889) proved an inspiration and a turning point in the lives of several of those who became important contributors to the development of biometry, statistics, and evolutionary biology.The imaginative psychological studies that he published in Inquiries into Human Faculty and its Development (1883), proved an important influence among psychologists.
Further Reading
Forrest DW (1974) Francis Galton: The Life and Work of a Victorian Genius. London: Paul Elek.
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Gayon J (1998) Darwin's Struggle for Survival, ch. 4. Cambridge: Cambridge University Press. Pearson K (1914±1930)The Life, Letters and Labours of Francis Galton, 3 vols. Cambridge: Cambridge University Press. Stigler S (1986)The History of Statistics: The Measurement of Uncertainty before 1900. Cambridge: Cambridge University Press.
See also: Darwin, Charles
Gametes J R S Fincham Copyright ß 2001 Academic Press doi: 10.1006/rwgn.2001.0492
Gametes are the haploid cells that fuse in the sexual life cycle to form the diploid zygote. Not all sexual organisms have gametes in the sense of specialized uninucleate cells, but they nevertheless contrive to bring haploid nuclei together for fusion (karyogamy), and we can refer to these as gamete nuclei. Not all gametes and gamete nuclei are differentiated into male and female, and not all are the immediate products of meiosis. In the majority of sexually reproducing organisms other than animals there is usually a haploid phase of mitotic division interposed between meiosis and sexual nuclear fusion, and in ferns, mosses, and liverworts, and most fungi and algae, the haploid phase is free-living. This article briefly reviews the variations found in different groups of sexually reproducing organisms.
Animals All groups of animals, other than the unicellular forms (Protozoa), have differentiated female eggs and male spermatozoa, the former contributing both nucleus and cytoplasm to the zygote and the latter little more than the nucleus. Both are the immediate products of meiosis, but whereas all four spermatozoa formed in a sperm mother cell (spermatocyte) are potentially viable, only one nucleus from meiosis in the oocyte survives in the egg, which is generally released from the ovary for fertilization as a free cell. The spermatozoa are each propelled by a single flagellum.
Variations in the Form of Gametes in Other Organisms All Gametes Motile in some (not all) Algae
In algae we see all the stages in the hypothetical evolution of male and female gametes from the supposed
primordial state of gametes of similar form and size. In some green algae, including the unicellular, motile Chlamydomonas reinhardtii, the gametes are motile biflagellate cells all the same size, though of two different mating types. In some related species, sexual fusion is between larger and smaller motile cells, which may be called male and female; the female gametes may, as in the colonial genus Volvox, lose their flagella and become nonmotile, so becoming more like eggs. Among the brown algae, some forms, such as the filamentous Ectocarpus, have equal-sized biflagellate motile gametes. The large brown seaweeds, exemplified by the genera Laminaria and Fucus and their allies, have nonmotile free-floating ova and motile sperm (called antherozoids). These genera are predominantly diploid, and the gametes in Fucus are the immediate products of meiosis. In the red algae there is another variation, with the male gametes not motile at all but rather nonmotile spermatia, which are released into the water in great numbers with the object of fusing with female receptive filaments which connect to the ova, which are retained within the female organ rather than allowed to drift. One well-studied group of Fungi, the Blastocladiales (e.g., Blastocladiella, Allomyces) can be mentioned here because of their remarkably alga-like mode of reproduction, with motile uniflagellated `male' and `female' gametes of different size.
Gametes and Vegetative Cells Interchangeable
In the budding yeasts such as Saccharomyces cerevisiae, the haploid products of meiosis are ready to function as gametes immediately, provided that different mating types come together (as they always do in strains with mating-type switching), but if restricted to one mating type they can bud indefinitely as vegetative haploid cells.
Ferns, Mosses, etc.: Male Gametes Motile
In both ferns and mosses, the female gametes are eggs held within female receptive structures (archegonia), while the male gametes are motile sperms, biflagellate in mosses but with many fine cilia in ferns. Two orders of much larger plants, the Cycadales and Ginkgoales, sometimes classified as distantly related to the gymnosperms (pine trees, etc.), also have multiciliated motile male gametes.
Seed Plants: Female Eggs and Male Gamete Nuclei The two main groups of seed plants, the angiosperms (flowering plants) and gymnosperms have egg cells
Galton, Francis
from turnover of galactose-containing complex glycoconjugates. Short-term 2-h oxidation of isotopic galactose to CO2 is very slow in most patients, but 24-h oxidative capacity is similar to that measured in normal patients after 5 h. The oxidative pathways involved have not been completely defined. This capacity to oxidize the sugar plus the urinary metabolite excretion maintain the patient in a steady-state with plasma galactose levels in the low micromolar range. The human galactose-1-phosphate uridyltransferase gene of 4 kb has been cloned and sequenced and consists of 11 introns and exons on chromosome 9. The cDNA codes for a 374 amino acid protein, with about 49% conservation between human and Escherichia coli enzymes. The active enzyme is a dimer with a molecular mass of 96 kDa. There are over 100 mutations known to occur in galactosemic patients. Most are missense mutations with a single base change, but stop mutations, splice site changes, frameshifts, and large deletions are found. The most common mutation, accounting for over 60% of mutant alleles, is Q188R, in which arginine is substituted for glutamine in the highly conserved region of exon 6. About 45% of patients are homozygous for Q188R. A number of Q188R alleles are compounded with other mutations. In African American and South African black galactosemics the prevalent mutation is S135L. The Q188R mutant is believed to be devoid of enzyme activity, while the S135L mutation results in residual liver enzyme activity. Heterodimer formation may be a significant determinant of enzyme activity. The N314D mutation with an asparagine to aspartic change is prevalent and the basis of the Duarte variant. It results in diminished but not absent erythrocyte enzyme activity and is itself benign. There appears to be no clear genotype±phenotype correlation. However, the ability to oxidize administered 1-13C galactose to 13CO2 of less then 2% in 2 h appears to indicate a more severe disorder as observed in many Q188R homozygotes than that present in compound heterozygotes. Neither the pathobiochemical basis of galactose toxicity in the newborn period, nor the late onset long-term diet-independent complications are known. Accumulation of galactose-1-phosphate and galactitol are believed to be responsible, but the mechanism of multiorgan involvement is unclear. Cataract formation is associated with galactitol accumulation. A knockout mouse with absent transferase activity shows no manifestations of the human phenotype, suggesting that absence of transferase is necessary but not sufficient to cause disease. This points to epigenetic factors and abnormal alternative pathway metabolites as the possible basis of the human disease.
The only known treatment of galactosemia has been restriction of lactose and other galactose-containing foods. Although the postnatal toxicity is alleviated, the long-term complications have not been averted. Speech therapy, special schooling, and hormonal therapy of ovarian failure are indicated and may be helpful. The disorder remains an enigma requiring the search for new therapeutic strategies. See also: Lactose
Galton, Francis R Olby Copyright ß 2001 Academic Press doi: 10.1006/rwgn.2001.0490
The Victorian intellectual Francis Galton (1822±1911) was one of the chief founders of the science of biometry, or the statistical and quantitative study of living things. He described its chief objective to be ``to afford material that shall be exact enough for the discovery of incipient stages in evolution,'' stages that are ``too small to be otherwise apparent.'' His goal was to establish the foundations upon which to base a policy to control and direct the future of mankind. In 1883 he coined the word `eugenics' for the science of improving stock, a term, he remarked, that is not confined to questions of judicious mating, but which especially in the case of man, takes cognizance of all influences that tend in however remote a degree to give to the more suitable races or strains of blood a better chance of prevailing speedily over the less suitable than they otherwise would have.
Galton was particularly concerned to show that the behavioral as well as the physical traits of mankind are inherited, that what is acquired in life cannot be passed to the offspring, and that nature (that which is inherited) has much more influence on the individual than has nurture (that which is gained from experience and education). He was, in other words, an `hereditarian.' But he did not simply make hereditarian claims. He developed the statistical techniques of regression and correlation to analyze the biometric data he collected from sampling human populations. His passion for quantitative treatment he also applied to establish weather patterns, to test the effectiveness of prayer, and to explore sensory perceptions, imagery, and memory. The zoologist Raphael Weldon and the mathematician Karl Pearson became devoted followers of
Galton, Francis 743 Galton. From the 1890s they vigorously developed the science of biometry, and in the early years of the twentieth century they opposed the newly rediscovered science of Mendelian heredity. Nearly two decades passed before biometry and Mendelism were effectively united to form what we call population genetics. Meanwhile Galton's science of eugenics passed through phases of popular approval and disapproval. The intensive study of the chemical sequence of the genetic material of our genes that has been ongoing since the 1980s has once more brought the subject of eugenics to popular attention. Could new and powerful techniques now make possible a kind of eugenics ``by the backdoor''? Not, in other words, public legislation enforcing eugenic policies, but covert pressures of the market through discrimination, and limited access to resources.
Francis Galton's Life Galton came of a wealthy and well-connected family, his mother being the daughter of Charles Darwin's grandfather, Dr Erasmus Darwin. As a boy and the youngest in the family, much affection was bestowed upon Francis, especially by his three sisters. AdeÁle, the youngest, acted as his tutor, and those around him soon considered him an infant prodigy. However, formal education, neither in France where he was sent at the age of eight, nor in England from the age of 14, proved to be to his liking. At 16 he began to study medicine, but two years later he turned to mathematics and moved to Cambridge. Four years later he gained a BA without honors and prepared to return to his medical studies. Then his father died, and he came into an inheritance that permitted him to forget medicine and indulge in his love of exploration. The resourceful and courageous young Galton traveled through Egypt, Syria, and South West Africa, where he covered some 1700 miles of uncharted country and came to know the Damara, Namaqua, and Ovampo tribes. He was struck by their distinctive behavioral and physical characteristics, and those of their domesticated animals. On his return to England in 1852 the Royal Geographical Society awarded him their gold medal for his achievement. During the 1850s he worked to promote geographical exploration, published his guide The Art of Travel (1855), introduced weather maps, discovered anticyclones, and worked for the British Association for the Advancement of Science. When in 1859 his cousin Charles Darwin published his book On the Origin of Species, Francis read it and was greatly impressed. If all life is the product of evolution, we should be able, given sufficient knowledge, to control our own evolution ± our future. But, like his cousin, he realized there
was a weak spot in the theory, the lack of sound knowledge of the nature of heredity. Accordingly, he turned in the 1860s to address this subject. Between 1865 and 1889 he worked often obsessively on gathering material. Publications on the subject flowed from his pen, the most important being his two books: Hereditary Genius (1869) and Natural Inheritance (1889). He lived on to 1911 ± long enough to seize the opportunity that the changing political climate of the new century afforded him to publicly appeal for the establishment and support of the science he called eugenics.
Human Heredity Conceptual
During the nineteenth century Herbert Spencer and Francis Galton gave up the term `inheritance' and following the French they substituted the term `heredity' (heÂreÂditeÂ). This signaled Galton's conception of heredity as based upon the continuity from generation to generation through an unbroken line not of persons but of the elements in the fertilized eggs from which they came. The term `inheritance' suggested the legal concept of the transmission of a person's estate to his descendants. Here the link is between the visible characteristics of the grown person (the parent) and the corresponding features of the offspring. But heredity is often indirect. The offspring bear similarities to many ancestors, not just to the parents. Moreover Galton was convinced that nothing we acquire in our organic constitution can thus be passed on. If we behave more virtuously, will our children do likewise? Do the sons of old soldiers, he asked in 1865, learn their drill more quickly than others, or the sons of fishermen escape sea-sickness? And if acquired characters are inherited, why have the many tribes of American Indians, though scattered over the vast range of different climates and situations of the Americas, remained much the same? Yet, if heredity is so unyielding, why is it that a father's characters are sometimes revealed in the son, sometimes in the daughter, or the child may bear the character seen only in a grandparent or more distant ancestor? How can so hard a process be so fickle? Galton saw that the answer lay in the statistical study of large numbers of ancestors and descendants, and in making an analysis of their statistical relations one to another. This is the heart of his project for what was later to be called biometry.
Observational
First he wanted to gather evidence that behavioral as well as physical characters are inherited. He chose to study what he called `genius,' or as he defined it, an
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ability that is ``exceptionally high, and at the same time inborn.'' It excludes any ability that can be attributed to the effects of education, but it includes an energetic disposition. Brilliance without application, persistance, and stamina, is of little use. Then he made the questionable assumption that ability correlates with eminence in public and professional life. Noting that great ability seemed to cling, as it were, to particular families like his cousin's, the Darwins, or the Bachs with its musicians and the Bernoullis with its mathematicians, he turned to the legal profession and extracted the names of 109 judges sufficiently eminent to be mentioned in Foss's Lives of the Judges (1865). Then he tracked the 85 families involved to establish how many relatives of these judges also achieved eminence in the legal or other professions. He found that one in every nine of these judges was either father, son, or brother to another judge, not to mention the relations of judges that attained higher legal office. He set out his results in tabular form (Table 1). The table illustrates how fewer and fewer relations of the most gifted member of a family attain to eminence the more distant is their kinship to that member. The percentages, wrote Galton, ``are quartered at each successive remove.'' He concluded that the data show ``in the most unmistakable manner the enormous odds that a near kinsman has over one that is remote, in the chance of inheriting ability.'' To consolidate this claim he turned to another eight professions, and to oarsmen and wrestlers. Most of the data were supportive of his claim, though he noted that some sons of very pious parents occasionally turn out extremely badly!
Methods in Population Studies Pedigrees
To the objection that Galton was ignoring the effects of nepotism, and the advantages of privileged upbringing and expensive education, he replied with the names of great men who, despite their lowly origin, had become eminent. This criticism, of course, struck at Galton's assumption that public eminence is a measure of native ability. He was aware of another problem, i.e., the underrepresentation of family data. This is the Achilles heel of the pedigree method, i.e., the use of family pedigrees for genetic data collection. Have some of the `failures' in life been left out? Are more representatives of the male kin included than those of the female? And how does one assess the contribution to ability coming from the females in the line using professional achievement at a time when the professions studied by Galton were not open to them? By the 1890s whole-population studies were being undertaken in Germany to escape such criticisms in the debate over the supposed inheritance of tuberculosis,
Table 1 The judges from 1660 to 1865. (From data in Galton (1889) Ancestral Inheritance.) ½ Great-grandfathers
7½ Grandfathers
½ Great-uncles
4½ Uncles
26 FATHERS
The most eminent members of 23 BROTHERS 1½ First cousins 100 distinguished families
36 SONS
4¾ Nephews
9½ Grandsons
2 Great-nephews
1½ Great-Grandsons
and in the 1870s Galton developed his famous method of twin studies in his effort to gather reliable evidence concerning the relative power of heredity and environment upon the shaping of the offspring. This has become one of the classic approaches whenever dealing with human traits, since the experimental approach is excluded.
Twin Studies
For his study of what he called ``The history of twins'' Galton used the questionnaire method. Darwin had circulated a questionnaire in his study of heredity and variation in the 1830s, and Galton had followed his example in his investigation into the upbringing and personal characteristics of Fellows of the Royal Society. His appeal for information about twins resulted in 35 adequately answered responses from parents of `closely similar' twins, and 20 from parents of `exceedingly unlike' twins. These allowed him to distinguish between what we call identical and non-identical twins. From this comparison of the two groups he concluded that ``nature prevails enormously over nurture when the differences of nurture do not exceed what is commonly to be found among persons of the same rank of society and in the same country.'' This was a wise qualification because he did not have data on twins reared apart either in identical or nonidentical environments. Subsequent researches by Galton's successors did extend the data collection in this way, but it is questionable how different were the environments of the separate homes in which the two members of each pair of twins grew up. In the 1970s the most extensive collection of twin data, that of the British psychologist, the late Sir Cyril Burt, was exposed as fraudulent. On a subject as politically sensitive as the heredity±environment equation, this
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Regression
Another method of central importance in the study of populations is that of the statistical distribution of traits. Galton was aware of the curve of `normal' distribution, also known as the Gaussian or error curve after the mathematician Gauss who applied it to the study of errors in astronomical measurement. Following Gauss, the Belgian Adolph Quetelet found that the measurement of the chests of 5738 Scottish soldiers and the stature of 100 000 French conscripts, when compared with the expectation from Gaussian curves, showed a ``marvelous concordance.'' The graph is bell-shaped, its top or plateau representing the median of the data (Figure 1), the median being that value which divides the data on either side equally and symmetrically. As an error curve the sides of the bell represent the `population' of error measurements, and the top itself is hopefully the `true' measurement. As a representation of the distribution of the soldiers' heights, Quetelet envisioned the top as marking the height of the `average man.' Those taller or shorter than this measure were `errors' as it were in attempts to copy the ideal of the race. The fact that these data fitted the error curve demonstrated, in his view, that they were homogeneous. Galton focused his attention less on the homogeneity of the population than on its variability. How, in spite of variability, did its median remain the same in successive generations, for of this he was already convinced? Therefore, he wanted to dissect the curve into its parts and follow the progeny of those parts. So he devised an exploratory study in which he got his friends to help by asking them to grow sets of sweet pea seeds (Lathyrus odoratus), which he had divided into seven classes by weight. They returned the crop to him and he was then able to plot the progeny seed weights against the weights of their respective parents. The result revealed the presence of a tendency of the progeny of heavy seeds to be lighter than their parents and those of lighter seeds to be heavier. There was a `reversion' toward the ancestral mean. Since the aggregate mean remained the same and because his helpers all lived in different parts of the British Isles he was confident that the data did not reflect the effects of environment. This tendency to counteract the extremes of individual variation by `shrinking' the excesses whether dwarfs or gaints in their progeny he called `reversion,' and later more wisely, `regression,' since reversion was the term already in use to refer to the return of the progeny of hybrids to their originating
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revelation had a damaging impact upon the field, but careful twin studies continue, particularly as a tool in the study of hereditary predispositions to diseases, including mental illnesses.
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Figure 1 Graph of the distribution of chest circumferences of 5732 Scottish militia men. The figure approximates to the bell-shaped curve of a `normal distribution.' (Redrawn from data in Quetelet (1817) Edinburgh Medical and Surgical Journal: 260±264.) species. Now he could understand why variability does not change the median or `center of gravity' of the population. Having established in a rough manner evidence for this regression in plants, Galton cast around for data on human characteristics, but in vain. However, when he advertized prizes of £500 for those who best filled in the elaborate set of questions that he prepared concerning them, their grandparents, parents, sisters, brothers, children, and other relatives, he was rewarded with a good response. These family records included stature of family members, so he was able to plot the statures of parents against offspring from which he calculated the regression (Figure 2). He expressed what he called the `coefficient of regression' as the ratio between the deviation of the offspring and that of the mid-parents from the population mean. This is measured on the graph by the distances AB and AC or EF and EG. Since the data fall approximately on a straight line, the ratio is constant throughout its length, giving a coefficient of regression of two-thirds. Now he had measured a statistical relation between two generations.
Correlation
Initially he considered regression in one direction only, but later realized that the regression of the parent on the child is the reciprocal of the child on the parent. Then in 1885 he hit upon the concept of `correlation,' namely that where there is a relation between the variation of one entity and that of another, they can be considered causally related. This important conception was developed more fully later by Karl Pearson.
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of fractional inheritance, according to which the parents collectively contribute one-half, the grandparents one-quarter, and the great-grandparents one-eighth to the hereditary constitution of the offspring. These ancestral contributions exert their influence and tend to bring back the progeny of deviants toward the mean of the ancestral population as a whole.
Discontinuous Variation
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Figure 2 Graph of the relation between the midparental heights of parents and the mean height of their children. The diagonal line represent all points on the graph corresponding to hypothetical parents and their children where the means of the children's heights are identical with their parents. The steeper line is plotted from Galton's data. The ratios AB:AC or EF:EG give the coefficient of regression. (Redrawn from Galton (1869) Hereditary Genius: An Inquiry into its Laws and Consequences, pp. 83. London: Macmillan.)
Natural Selection Stabilizing Selection
Darwin had focused upon the slight individual differences that constitute the variation to be found among members of a family and of a species. ``They afford material,'' he said, ``for natural selection to accumulate, in the same manner as man can accumulate in any given direction individual differences in his domesticated productions.'' But Galton was convinced that natural selection cannot work effectively against heredity, and he considered that his work was showing heredity maintaining the racial mean. According to Galton, the mean is the adapted form and deviations from it will be less adapted to the conditions of life. Therefore, natural selection will be aiding heredity in preserving it. In other words, he granted natural selection its `stabilizing' role, but not its `creative role.' As the reason for this state of affairs he turned to the physiology of reproduction. The fertilized egg is composed of hereditary material from two parents, so that each time a new generation is produced there is a bringing together of two such materials. Inevitably the contributions of each parent and each ancestor will be diluted. So he accepted the long-held tradition
Having thus restricted the role of natural selection, he turned to `sports' of nature, those marked deviations that possess a stability shown by the absence of regression to the existing type among their progeny. These deviations create a new mean toward which any progeny will tend to regress instead of regressing toward the mean of the original population. Hence, he explained, these sports may give rise to a new race with but little help from natural selection. He was thus opposed to cousin Darwin who in his On the Origin of Species had stressed how unlikely it was that such sports could serve as the starting point for new species. Granted they were strongly inherited, but most sports were closer to monstrosities than to newly adapted forms. In any case, thought Darwin, their rarity would result in the dilution of their type in successive generations of breeding with other members of the species. Darwin proved to be largely right on his first objection, but wrong on his second. It should not be assumed that Galton's apostasy over natural selection was unusual for the nineteenth century. The consensus was in favor of evolution by descent, but not under the principal agency of natural selection. Therefore, it is ironic that those who most strongly supported the pre-eminence of natural selection considered themselves Galton's successors. Thus Karl Pearson and Raphael Weldon developed Galton's statistical techniques and corrected his errors. But when Weldon sought to demonstrate natural selection in its creative role, shifting the mean of a population, he only succeeded in demonstrating its stabilizing role. Pearson exposed some of the confusions in the several differing representations of the ancestral law offered by Galton. He corrected the figure of twothirds for the regression of offspring on parents, explained why regression was not the barrier to selection that Galton claimed, and explored the effects of `assortative' mating, i.e., the choice of mates based on similarities of ability and background, which promotes the shifting of the mean of the resulting offspring further and further away from that of the general population.
Finger Prints
The minute and distinctive patterns of ridges on the skin were used to make finger prints before Galton
Galton, Francis 747 took up the subject. But it was he who conducted a systematic study leading to his classification of the differing types and it was he who persuaded the police to adopt the practice of fingerprinting for personal identification of criminals. For Galton the subject had a compelling theoretical interest because the trait appeared to have no function such that natural selection could act upon it. Marriage selection does not depend on it; the different patterns are not confined to particular classes or races. Therefore, there is complete `promiscuity' with respect to this trait. Yet the varieties remain distinct. Here, then, we have a trait whose varieties do not blend and are not subject to selection. This, he believed, was an example of the existence and persistence of distinctive types independent of selection. Of course he could not really have known whether the trait was connected to some other trait that is subject to natural selection.
Eugenics Controlling our Evolution
The driving force behind Galton's extensive and longcontinued research was not just his curiosity, great as that was, but his vision of a future in which mankind would attain to greater energy and coadaptation. But he realized how easy it was to follow the wrong course. To accept the evolutionary process passively would be to surrender to ``blind and wasteful processes'' in which raw material is produced extravagantly and all that is superfluous is rejected ``through the blundering steps of trial and error.'' He favored the alternative that we should take control of our evolution, for it may be that we are the ``only executives on earth.'' Hence the importance of eugenics in providing the proper scientific basis for action. To support such work he settled an endowment on University College London so that in 1905 a Research Fellow in eugenics could be appointed. Further expansion led to the creationoftheEugenicsLaboratory.In1911,againthrough Galton's munificence, a chair of eugenics was established at the College, the first occupant being Pearson.
Victorian Attitudes
Galton's attitude to racial differences, to women, and to the indigent was typical of a wealthy Victorian. Mild of manner and gentle in his disposition, yet his attitude to the less fortunate was unquestionably harsh. Many at the time endorsed the policy of negative eugenics, i.e., to discourage the marriage and procreation of offspring by the exceptionally unfit, but Galton went further and wanted to favor those families that were ``exceptionally fit for citizenship.'' He argued that since there was substantial giving to the poor and destitute, could not support be forthcoming
to promote ``the natural gifts and the national efficiency of future generations''? His concern, like Pearson's, was over the differential between the reproductive rates of the upper middle and lower classes in favor of the latter.
Publicizing Eugenics
In 1904 the time was judged opportune for Galton to address the Sociological Society on eugenics. Here he argued for the maintenance of diversity, but ``each class or sect'' represented ``by its best specimens,'' and then to leave them to ``work out their common civilization in their own way.'' The best were the healthy, the energetic, the able, the manly (!), the courteous, but he advised leaving out the cranks and refusing the criminals. Eugenics should study the conditions that cause families to thrive and leave more descendants, so that the most useful members of society could be encouraged to adopt such conditions. The main task ahead was to establish eugenics as an academic question, then to bring about consideration of its practical development, and third to introduce eugenics ``into the national conscience, like a new religion.'' He ended by cautioning his audience against too much zeal which could lead to hasty action. A golden age is not round the corner, he warned. Such expectations would lead to discrediting of the science. In the event it took Hitler's treatment of the Jews in World War II to achieve that.
Conclusion Galton was the confident English gentleman, well aware of the superiority of his nation and his class, condescending to the former colonies, and dedicated to turning back the degeneration of his countrymen. But he disparaged the institution of the aristocracy, rejected the Christian religion, and considered many of our behavioral characteristics as outworn relics from a primitive stage in our social evolution. Although his mathematical skills were limited, his imagination, insight, and inventiveness were remarkable. Allied to his incessant curiosity, these talents made him one of the founders of the statistical revolution that occurred in his lifetime. His book Natural Inheritance (1889) proved an inspiration and a turning point in the lives of several of those who became important contributors to the development of biometry, statistics, and evolutionary biology.The imaginative psychological studies that he published in Inquiries into Human Faculty and its Development (1883), proved an important influence among psychologists.
Further Reading
Forrest DW (1974) Francis Galton: The Life and Work of a Victorian Genius. London: Paul Elek.
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G a m et e s
Gayon J (1998) Darwin's Struggle for Survival, ch. 4. Cambridge: Cambridge University Press. Pearson K (1914±1930)The Life, Letters and Labours of Francis Galton, 3 vols. Cambridge: Cambridge University Press. Stigler S (1986)The History of Statistics: The Measurement of Uncertainty before 1900. Cambridge: Cambridge University Press.
See also: Darwin, Charles
Gametes J R S Fincham Copyright ß 2001 Academic Press doi: 10.1006/rwgn.2001.0492
Gametes are the haploid cells that fuse in the sexual life cycle to form the diploid zygote. Not all sexual organisms have gametes in the sense of specialized uninucleate cells, but they nevertheless contrive to bring haploid nuclei together for fusion (karyogamy), and we can refer to these as gamete nuclei. Not all gametes and gamete nuclei are differentiated into male and female, and not all are the immediate products of meiosis. In the majority of sexually reproducing organisms other than animals there is usually a haploid phase of mitotic division interposed between meiosis and sexual nuclear fusion, and in ferns, mosses, and liverworts, and most fungi and algae, the haploid phase is free-living. This article briefly reviews the variations found in different groups of sexually reproducing organisms.
Animals All groups of animals, other than the unicellular forms (Protozoa), have differentiated female eggs and male spermatozoa, the former contributing both nucleus and cytoplasm to the zygote and the latter little more than the nucleus. Both are the immediate products of meiosis, but whereas all four spermatozoa formed in a sperm mother cell (spermatocyte) are potentially viable, only one nucleus from meiosis in the oocyte survives in the egg, which is generally released from the ovary for fertilization as a free cell. The spermatozoa are each propelled by a single flagellum.
Variations in the Form of Gametes in Other Organisms All Gametes Motile in some (not all) Algae
In algae we see all the stages in the hypothetical evolution of male and female gametes from the supposed
primordial state of gametes of similar form and size. In some green algae, including the unicellular, motile Chlamydomonas reinhardtii, the gametes are motile biflagellate cells all the same size, though of two different mating types. In some related species, sexual fusion is between larger and smaller motile cells, which may be called male and female; the female gametes may, as in the colonial genus Volvox, lose their flagella and become nonmotile, so becoming more like eggs. Among the brown algae, some forms, such as the filamentous Ectocarpus, have equal-sized biflagellate motile gametes. The large brown seaweeds, exemplified by the genera Laminaria and Fucus and their allies, have nonmotile free-floating ova and motile sperm (called antherozoids). These genera are predominantly diploid, and the gametes in Fucus are the immediate products of meiosis. In the red algae there is another variation, with the male gametes not motile at all but rather nonmotile spermatia, which are released into the water in great numbers with the object of fusing with female receptive filaments which connect to the ova, which are retained within the female organ rather than allowed to drift. One well-studied group of Fungi, the Blastocladiales (e.g., Blastocladiella, Allomyces) can be mentioned here because of their remarkably alga-like mode of reproduction, with motile uniflagellated `male' and `female' gametes of different size.
Gametes and Vegetative Cells Interchangeable
In the budding yeasts such as Saccharomyces cerevisiae, the haploid products of meiosis are ready to function as gametes immediately, provided that different mating types come together (as they always do in strains with mating-type switching), but if restricted to one mating type they can bud indefinitely as vegetative haploid cells.
Ferns, Mosses, etc.: Male Gametes Motile
In both ferns and mosses, the female gametes are eggs held within female receptive structures (archegonia), while the male gametes are motile sperms, biflagellate in mosses but with many fine cilia in ferns. Two orders of much larger plants, the Cycadales and Ginkgoales, sometimes classified as distantly related to the gymnosperms (pine trees, etc.), also have multiciliated motile male gametes.
Seed Plants: Female Eggs and Male Gamete Nuclei The two main groups of seed plants, the angiosperms (flowering plants) and gymnosperms have egg cells