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1909 Non-Mendelian Inheritance
Chapter 13
1909 Non-Mendelian Inheritance
5 5
10
THE STANDARD PARADIGM Genes in higher organisms tend to obey Mendel’s laws of segregation and independent assortment. (Actually, however, this paradigm had existed only for the few years following the rediscovery of Mendel’s work at the turn of the century, because at that time Mendelian principles had been documented in only a few organisms such as pea plants [see Chapter 3] and humans [see Chapter 8].)
THE CONCEPTUAL REVOLUTION Carl Correns and Erwin Baur, working independently, were the first to describe a hereditary mode (in this case involving plant plastids) that did not conform to Mendel’s rules. These scientists had uncovered examples of maternal inheritance wherein traits are transmitted to seedlings through the mother only, with the pollen-providing parent apparently having no influence on the phenotype of the progeny. The authors correctly concluded that in addition to Mendelian genes in the cell nucleus, additional hereditary factors must occur in the cellular cytoplasm that comes mostly from the egg. Today, we understand that such hereditary factors reside in the chloroplast genomes (cpDNA) of plants and in the mitochondrial genomes (mtDNA) of animals and plants (see Chapter 38).
PS-score: 5 In the full century following Correns and Baur, many more categories and countless examples of non-Mendelian heredity in eukaryotic organisms have J.C. Avise: Conceptual Breakthroughs in Evolutionary Genetics. DOI: http://dx.doi.org/10.1016/B978-0-12-420166-8.00013-0 © 2014 Elsevier Inc. All rights reserved.
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PART | I
The First 50 Years (1859 1910): Laying the Foundations
come to light. For example, gene conversion is a type of non-Mendelian heredity in which one allele at a locus converts (via mismatch repair) to the DNA sequence of the other allele at that diploid locus. Such gene conversion can be considered one category of meiotic drive or molecular drive wherein one allele out-competes the other for transmission to the next organismal generation (see Chapter 48). Somewhat analogously, genetic recombination events between loci are also known, and these sometimes can lead to a form of “concerted” evolution in which paralogous members of a gene family tend to evolve in concert within a species, with respect to their nucleotide sequences. Notwithstanding the near-universality of non-Mendelian maternal inheritance for cytoplasmic genomes, and the diversity of other non-Mendelian hereditary mechanisms subsequently uncovered, the fact remains that Mendel’s laws as originally formulated remain applicable to a vast majority of nuclear loci in most eukaryotic species. Thus, Mendelian heredity remains the rule rather than the exception, accounting for why I have given the discovery of non-Mendelian inheritance only an intermediate PS-score.
REFERENCES AND FURTHER READING Baur E. 1909. The nature and the inheritance properties of horticultural varieties of Pelargonium zonale having white borders [original title was in German]. Zeitschr. f. ind. Abst. u. Vererbungsl 1:300 351. Correns C. 1909. Inheritance experiments with pale (yellow) green and variegated varieties of Mirabilis julapa [original title was in German]. Zeitschr. f. ind. Abst. u. Vererbungsl 1:291 329. Dover GA. 1982. Molecular drive: a cohesive mode of species evolution. Nature 299:111 117. Liao D. 1999. Concerted evolution: molecular mechanism and biological implications. Amer. J. Human Genet. 64:24 30. Hagemann R. 2000. Erwin Baur and Carl Correns: Who really created the theory of plastid inheritance? J. Heredity 91:435 440. Chen JM, Cooper DN, Chuzhanova N, Fe´rec C, Patrinos GP. 2007. Gene conversion: mechanisms, evolution, and human disease. Nature Rev. Genet. 8:762 775.
1909 Non-Mendelian Inheritance
5 5
10
THE STANDARD PARADIGM Genes in higher organisms tend to obey Mendel’s laws of segregation and independent assortment. (Actually, however, this paradigm had existed only for the few years following the rediscovery of Mendel’s work at the turn of the century, because at that time Mendelian principles had been documented in only a few organisms such as pea plants [see Chapter 3] and humans [see Chapter 8].)
THE CONCEPTUAL REVOLUTION Carl Correns and Erwin Baur, working independently, were the first to describe a hereditary mode (in this case involving plant plastids) that did not conform to Mendel’s rules. These scientists had uncovered examples of maternal inheritance wherein traits are transmitted to seedlings through the mother only, with the pollen-providing parent apparently having no influence on the phenotype of the progeny. The authors correctly concluded that in addition to Mendelian genes in the cell nucleus, additional hereditary factors must occur in the cellular cytoplasm that comes mostly from the egg. Today, we understand that such hereditary factors reside in the chloroplast genomes (cpDNA) of plants and in the mitochondrial genomes (mtDNA) of animals and plants (see Chapter 38).
PS-score: 5 In the full century following Correns and Baur, many more categories and countless examples of non-Mendelian heredity in eukaryotic organisms have J.C. Avise: Conceptual Breakthroughs in Evolutionary Genetics. DOI: http://dx.doi.org/10.1016/B978-0-12-420166-8.00013-0 © 2014 Elsevier Inc. All rights reserved.
27
28
PART | I
The First 50 Years (1859 1910): Laying the Foundations
come to light. For example, gene conversion is a type of non-Mendelian heredity in which one allele at a locus converts (via mismatch repair) to the DNA sequence of the other allele at that diploid locus. Such gene conversion can be considered one category of meiotic drive or molecular drive wherein one allele out-competes the other for transmission to the next organismal generation (see Chapter 48). Somewhat analogously, genetic recombination events between loci are also known, and these sometimes can lead to a form of “concerted” evolution in which paralogous members of a gene family tend to evolve in concert within a species, with respect to their nucleotide sequences. Notwithstanding the near-universality of non-Mendelian maternal inheritance for cytoplasmic genomes, and the diversity of other non-Mendelian hereditary mechanisms subsequently uncovered, the fact remains that Mendel’s laws as originally formulated remain applicable to a vast majority of nuclear loci in most eukaryotic species. Thus, Mendelian heredity remains the rule rather than the exception, accounting for why I have given the discovery of non-Mendelian inheritance only an intermediate PS-score.
REFERENCES AND FURTHER READING Baur E. 1909. The nature and the inheritance properties of horticultural varieties of Pelargonium zonale having white borders [original title was in German]. Zeitschr. f. ind. Abst. u. Vererbungsl 1:300 351. Correns C. 1909. Inheritance experiments with pale (yellow) green and variegated varieties of Mirabilis julapa [original title was in German]. Zeitschr. f. ind. Abst. u. Vererbungsl 1:291 329. Dover GA. 1982. Molecular drive: a cohesive mode of species evolution. Nature 299:111 117. Liao D. 1999. Concerted evolution: molecular mechanism and biological implications. Amer. J. Human Genet. 64:24 30. Hagemann R. 2000. Erwin Baur and Carl Correns: Who really created the theory of plastid inheritance? J. Heredity 91:435 440. Chen JM, Cooper DN, Chuzhanova N, Fe´rec C, Patrinos GP. 2007. Gene conversion: mechanisms, evolution, and human disease. Nature Rev. Genet. 8:762 775.