Morphogenetic Studies of the Rabbit. Xxiii. the Effects of the Dachs Gene Da (Chondrodystrophy) upon Linear and Lateral Growth of the Skeleton as Influenced in Time.

NHERITED skeletal abnormalities which may be, and have been, classifiei I fundamentally as the result of disproportionate reduction of localized parts manifest a wide range of species patterns with respect to the degree and location of effect upon the skull and limbs, and in some cases the vertebrae. When homozygous these abnormalities are lethal at a relatively early age in the most severely affected, such as the Creeper fowl. (LANDAUER 1932) achondroplastic rabbit (ac ) , (PEARCE and BROWN 1945), and certain of the cattle dwarfs. They vary considerably in their expression when heterozygous from almost none to obvious abnormality, whereas animals such as the Bassett hound and Dachshund (commonly considered disproportionate dwarfs) are able to live apparently normal lives though homozygous. Between these two groups is the dachs rabbit (SAWIN and CRARY 1957) which is neither a severe and early lethal, nor one which can be said to live out as a breed a relatively complete and normal life span. I n some genomes the gene induces (when homozygous) a severe crippling, whereas in others it permits survival to adulthood and production of viable young, although few of the young so produced can be raised without a foster mother. Thus, considering the disproportionate dwarfs as a group, there is a wide range of variation, both with respect to time of onset of gene effect and to its effect upon the life span. That time is an important factor in the expression of such anomalies was brought out by STOCKARD ( 1941 ) on dogs, and particularly by LANDAUER (1 934) in early studies of the Creeper fowl. The latter repeatedly emphasized this fact again in connection with “Brachypodism” in mice ( LANDAUER 1952). Although the number of cases in which onset and duration of action are at all pinpointed in time is almost exclusively restricted to LANDAUER’S work, our recent studies of the dachs gene (CRARY and SAWIN 1958) have demonstrated quantitative changes which in this case at least suggest a more extensive effect of the gene in time than has been demonstrated in any previously described case. The importance of differential species patterns of development has been summarized by LANDAUER (1952). These suggest the importance of study of dissimilarities of the normal and abnormal growth patterns in time. LANDAUER has