The Independence of Dominant Spotting and Recessive Spotting ("Piebald") in the House Mouse.

In 1919 Castle" 2 showed the dominant English spotting pattern of the rabbit to be closely linked with the recessive Dutch spotting pattern, and in 1924 he published evidence proving that both English and Dutch are linked with Angora. In the latter year I began experiments designed to learn whether or not there exists a corresponding linkage between dominant and recessive spotting in the house mouse. Dunn3 (1920) had previously published data upon the subject. Both Dunn's data and my own collected during three years seemed inconclusive on account of difficulties in classification. It is impossible by inspection to classify correctly all animals containing certain combinations of the dominant and recessive spotting factors and their allelomorphs because most genetic classes overlap in their somatic appearance. Dr. Geo. D. Snell4 has shown that recessive piebald (ss) and recessive hairless (hr hr) are linked with about 10% crossing-over. Thus, recessive hairless (hr hr) may be used as a check in the identification of recessive piebald (ss) animals if it is introduced into the cross in association with piebald. Piebald animals (ss) will then lose their hair at about two weeks after birth whereas animals not containing two doses of piebald will retain their hair, unless a cross-over has occurred. By this control we may be certain of the classification of 90% of the piebald young. Data employing this check should provide conclusive evidence upon the question of the genetic relationship between dominant and recessive spotting. The three pairs of gene allelomorphs dealt with in this paper are