Dwarfism

Dwarfism, in Mice 591 they suppressed normal recombination between T and nearby markers. He went on to describe over 100 such chromosomes that were ultimately found to contain six different lethals. Starting in 1935, along with a colleague Salome Glueckshon-Waelsch, he described the embryology of many different t lethal syndromes. The most blatant defiance of Mendel's rule of independent assortment was the fact that t haplotypes, as they later came to be called, suffered from transmission ratio distortion through males, so that over 90% of their progeny, instead of the expected 50%, carried the t. This phenomenon, which is still poorly understood, explains the maintenance of these mutations in wild populations of mice. During his Emeritus days and well into his retirement at the Nevis Biological Station of Columbia, Dunny worked actively in his mouse room and wrote extensively. As a young graduate student of his longtime colleague D. Bennett, I first encountered him in 1968 on his knees on the Nevis barn floor chasing an escapee wild mouse from Novosibirsk. He labored with love in that mouse room until he died there in 1974 at the age of 80. Dunn's perspective in the history of biology was a unique one. He spanned the age of the rediscovery of Mendel to the birth of molecular biology. Without understanding the significance at the time, he married the precise study of genetics to developmental biology. In that sense he debunked an intellectual dichotomy that in some corners was debated seriously until the advent of modern molecular biology, which unequivocally united the areas of developmental biology and genetics. As if a prophet, he commented on the progress of genetics in a presidential address presented at the 1961 meeting of the American Society of Human Genetics: What we may be witnessing now is only the beginning of a kind of renaissance . . . What seems to be most important, especially in its implications for the future, is the growing recognition of the logical unity of genetics . . . being concerned with a system of elements having similar attributes in all forms of life, can be seen to transcend the special problems of different categories of organisms.

Dunn thought and wrote broadly about scientific history, philosophy, and the human condition. He was indeed the renaissance geneticist.

Further Reading

Bennett D (1977) L.C. Dunn and his contribution to T-locus genetics. Annual Review of Genetics 11: 1±12.

See also: Brachyury Locus

Dwarfism K M Beckingham Copyright ß 2001 Academic Press doi: 10.1006/rwgn.2001.0389

Mutations that stunt growth and produce individuals with markedly reduced height, or dwarfism, are known in many species. One of the seven genetic traits originally analyzed by Mendel in his formulation of the laws of inheritance was dwarfism in the garden pea. Recently, Mendel's dwarf mutation has been shown to affect production of the hormone gibberellin, which is essential for internode elongation. In humans, mutations in at least 320 genes can cause short stature often in conjunction with other abnormalities. The most common form of human genetic dwarfism, achondroplasia, causes disrupted development of the long bone growth plates, producing disproportionate shortness of the limbs. In dogs, this defect is responsible for the distinctive body form of the dachshund and the basset hound. Human achondroplasia mutations are dominant mutations to the gene for fibroblast growth factor receptor 3 (FGFR3). Many of these human mutations appear to be spontaneously generated in a parental germline cell. See also: Achondroplasia

Dwarfism, in Mice K Douglas and S A Camper Copyright ß 2001 Academic Press doi: 10.1006/rwgn.2001.0388

Many spontaneous mouse mutants with growth insufficiency, or dwarfism, phenotypes exist. The genes mutated in these mice are important for normal growth regulation in mice and other mammals (Watkins-Chow and Camper, 1998). Several tissues are critical for normal growth. The hypothalamus secretes releasing factors that act directly on the adjacent pituitary gland. The pituitary, in response to hypothalamic signals, secretes hormones into the peripheral bloodstream. Finally, target organs act in response to the presence of pituitary hormones in the bloodstream. Target organs may also secrete factors that feed back to the hypothalamus and pituitary gland in order to regulate secretion of hormones.