The Relation of Yellow Coat Color and Black-Eyed White Spotting of Mice in Inheritance.

C U ~ N O T , STURTEVANT and MORGAN have all shown that a series of mutually allelomorphic forms of coat pattern exists in mice. There are four types of pattern in this series. These in order, from the most hypostatic to the most epistatic, are as follows: ( I ) Non-agouti, the ordinary “self” or “unticked” coat pattern. ( 2 ) Agou t i or better graybellied agouti, the coat pattern seen in the ordinary wild house mouse. (3) White-bellied agouti, in which there is a decrease in brown and black pigmentation resulting in more yellow on the dorsal surface and white-tipped ventral hairs. (4) The final member of the series, the yellow coat pattern in which almost, if not all, the brown and black pigment of the coat has disappeared and is replaced by yellow. It is easy to obtain mice homozygous for any of the three lower members of the series : non-agouti, gray-bellied agouti, and white-bellied agouti. No one, however, has yet obtained yellow mice which are homozygous. There is every reason to believe that the process of fertilization between two yellow-bearing gametes occurs ( CASTLE and LITTLE 1910). The ratio of yellow to non-yellow young, however, makes it certain that the homozygous yellow zygotes do not reach a sufficiently advanced age to enable one to record them (CASTLE and LITTLE 1910, LITTLE 1911, DURHAM 1911, DUNN 1916). The size of litters when yellows are crossed inter se is also smaller than when yellows are crossed with any of the hypostatic types (CAsrLE and LITTLE 1910, DURHAM 1911, DUNN 1916). If we are to consider that allelomorphs occupy the same locus in the chromosome we are faced with a condition somewhat as follows. Four distinct stages occur in the restriction of brown and black pigment from the coat. The first three stages, though they cover a wide range of variation in extent of brown and black pigmentation, may all of them .be obtained in a homozygous condition. The fourth step, however,