MORPHOGENETIC STUDIES OF THE RABBIT. XXXV. PLEIOTROPIC EFFECTS OF THE DACHS GENE AND THE GRADIENT GROWTH PATTERN.

Abstract

AbstractThe pleiotropic effects of the dachs gene (Da) upon the skeleton have been studied in alizarin stained preparations and roentgenograms in 412 skeletons of progeny (aged 31–90 days) of three possible genotypes obtained from heterozygous parents. Basically they arise as direct or indirect manifestations of retardation, including reductions in size, deficiency in numbers of skeletal units, compensatory induction of accessory units, and overgrowth of adjacent normal units. These lead to homeotic shifts or displacement in position, crowding, and fusion. Vertebral borders anterior to v. 20 are displaced forward; those posterior tend to be backward, and the initial appearances of the epiphyses are also affected. Epiphyses of the vertebrae and long bones and the carpals and tarsals as maturity indicators are precocious as they are in retarded conditions of man, and this is enhanced in heterozygotes simulating overdominance or one gene heterosis. As indicators of premature maturation they have semblance of dysheterosis. Of particular significance is the manner in which these diverse pleiotropic effects exemplify the genetic concept of overdominance, modify the species or strain gradient pattern and the similarities of the mechanism of action to processes already revealed experimentally in the laboratory by various investigators. Extension of such study by qualitative and quantitative methods opens an approach to both genetic and environmental factors affecting normal and abnormal growth which can be tested in many ways. It would be particularly effective in study of the syndrome of effects induced by radiation, hypoxia, and other teratogenic agents.