A new sub-lethal colour mutation in the house mouse

Abstract

This new auto-somal recessive factor suppresses the yellow pigment in the coat and kills the homozygotes in the 4th week of life. A study of the growth curves led to the discovery that the "grey-lethals" do not cut their teeth. Death, however, is not due to failure in cutting teeth, since the animals die, although later, when fed on a liquid diet. The study of the skeleton revealed a complex of symptoms not parallelel in human pathology. There is a complete lack of all secondary absorption processes in the bones: every spicule once laid down is preserved permanently. This leads to very characteristic anomalies of bone and skull shape. In addition, the calcification of individual spicules is incomplete. Incomplete calcification of the dentine accounts for the non-eruption of the teeth. Their roots remain uncalcified and become complexly bent and wrinkled. The growth tendency of the lower incisor is unlimited; the very dense spongiosa of the mandible against which it is growing causes it to find an abnormal way out. It grows in fact through the mental foramen which gets enormously enlarged and filled by the irregularly shaped outgrowth of that tooth. The shape of the teeth is more or less abnormal, and the snout skeleton considerably shortened owing to the poor development of the upper incisors. A secondary effect is deviation of the nasal septum owing to uncoordinated growth of osseous and cartilaginous parts. A general arrest in growth is observed after the first 2 weeks.