A Fifth Allelomorph in the Agouti Series of the House Mouse.

Experiments with a strain of black-and-tan mice obtained from an English fancier* 'have shown that these mice contain a hi-therto undescribed gene which is allelomorphic to yellow, agouti, and non-agouti (black}, and: consequently forms a fifth member of this series of multiple allelomorphs. The black-and-tans used are jet black dorsally with a bright yellow belly and retain this coloration throughout life. They breed true and produce large litters averaging about 7.5 young per litter. When crossed with black mice they produce only black-and-tans indistinguishable from the pure type. Such F1 animals niated inter se produce only black-and-tans and blacks in a monohybrid ratio (actual numbers 80:31). Crossed with agouti (wild type) they produce only agoutis with yellow bellies. The cross of black-and-tan with yellow (heterozygous for agouti) yields two types of young in about equal numbers; viz., yellows or sables (dark yellows and yellow-bellied agoutis (actual 'numbers 19:22). The F1 yellows or sables crossed with black produce equal numbers of yellows (or sables) and black-and-tans (67 of each in the experiments to date) showing that the F1 sable or yellow type is heterozygous only for yellow and black-andtan, and that yellow and black-and-tan are allelomorphs. The F1 yellowbellied agoutis wben crossed with black produce only black-and-tans and gray-bellied agoutis (ratio 74:95) showing that black-and-tan and agouti are allelomorphs. The cross of black-and-tan with white-bellied agouti (a dominant allelomorph of the wild type) produces agoutis with bellies intermediate between yellow and white. These results indicate that the gene for black-and-tan is allelomorphic to yellow, agouti, white-bellied agouti and non-agouti. It is completely dominant to non-agouti, the lowest member of the series; in its effect on the dorsal pigmentation it is recessive to wild type, white-bellied agouti and yellow, so that from this standpoint the order of dominance in this series may be written as follows: