Genetical and Developmental Studies on Droopy-eared Mice

Abstract

ABSTRACT Droopy-ear is a single, recessive, autosomal gene with full penetrance. Droopy-ear is linked to Varitint p27 ± 3·2, but segregates independently of the other genes tested. In adult droopy-eared mice the areas of specific abnormalities are the occiput and the shoulder girdle. The rest of the skeleton shows immaturity of form, and disproportionate shortening of the limb bones. The anomalies of the adult skeleton are traced back, through a delay in ossification, to a delay in chondrification and localized areas of abnormal cartilage, and thus back to disturbed mesenchymal condensations, which in some cases are also thin. Certain of the abnormalities, in particular the splitting of the dens epistrophei into two parts, one of which may be attached to the basioccipital, strongly recall the anatomical situation in the more primitive vertebrates. Some anomalies of the internal bone structure are described. The droopy-ear syndrome is considered in relation to the syndromes of the other mouse mutants whose mesenchymal condensations are disturbed. The similarities of the droopy-ear syndrome with some conditions in other chondrodystrophic disorders is noted. The theories concerning the localization of specific abnormalities are discussed in relation to droopy-ear.