STUDIES ON AN ANOPHTHALMIC STRAIN OF MICE. III. RESULTS OF CROSSES WITH OTHER STRAINS

Abstract

EYELESSNESS has been found in individuals throughout the verte- E brates, and blind species are known in almost all classes. This strain of eyeless mice is more extreme in eye reduction than any blind species. It provides an opportunity for the study of factors affecting the expression of this character which in turn may help in understanding the phylogeny of blind species. With selection and inbreeding, the hereditary minor factors (modifiers) have become practically homozygous, thus making possible an analysis of the heredity of eyelessness without the confusion of unpredicted modifiers. Two methods of analysis of the mode of inheritance of this eyelessness have been undertaken. The present paper deals with the inheritance when the modifiers are not the same-that is, crosses with different strains of mice. Another method involves a control of the modifiers, made possible by a mutation toward normal eyes in the inbred eyeless strain. This study is in progress at the present time. The embryology of this anophthalmia has been shohrn to be fundamentally an inhibition of the growth of the optic vesicle at ten days or earlier, just after the normal formation of the vesicle (CHASE and CHASE 1941). This inhibition may prevent the vesicle from forming a cup; or, more often, a small, irregular cup forms, usually too far from the surface to induce a lens. Whatever is present by 13 days usually grows at a normal rate with the remainder of the embryo but is too’late to organize into a normal functional eye. The variations result in the adult in (I) complete anophthalmia with no eye remnants but with normal lids, orbits, and conjunctivas and large lacrimal glands (actually Harderian glands) filling the normal eye sockets; (2) a “very small” eye of only a pigment mass or with a little abnormal retinal tissue in addition; (3) a “small” eye with lens and abnormal retina; or (4) a “medium” eye with normal proportions. The medium eye can be seen between the lids; small and very small eyes cannot. Reproduction in this strain is not affected (E. B. CHASE 1941). Lack of eyes and optic nerves are apparently no detriment to normal reproductive behavior in these animals.