Interlitter variation in progeny of chimaeric male mice

Three chimaeric male mice (C57BL/6McL reversible BALB/c) were allowed to mate freely with BALB/c females, and produced two types of progeny: agouti (BALB/c egg X C57BL spermatozoon) and albino (BALB/c egg X BALB/c spermatozoon). The proportion of each type, however, varied significantly from litter to litter. The variation could not be related to the age of the male, or to the particular female who produced the litter, nor had it a clear cyclic pattern. Unilateral orchidectomy of one male resulted in a change in the overall frequency of progeny types observed, but did not alter the degree of interlitter variation. Females were then introduced to two of the males overnight (18:00-09:00 h) or during the day (09:00-18:00 h) in mouse rooms with a dark period from 19:00 to 05:00 h. Overnight matings produced a slight increase in the proportion of albino progeny, but daytime matings resulted in a significant increase in agouti young (P less than 0.001). The relative proportions of the two types of progeny in litters of these males therefore appeared to be affected by the time of mating relative to the time of ovulation in the female, suggesting that variation in the time of mating is responsible for the observed interlitter variation in progeny type. Electrophoretic analysis of GPI-1 from spermatogenic cells isolated from the testes of one of the chimaeric males after death showed that the proportions of the two cell types in the testes were closer to the progeny proportions obtained from overnight than from daytime matings.