Abstract
When male mice from inbred PHH (sex ratio .535) and PHL (.435) are mated to females of various inbred lines, the sex ratio follows the male parent. The sex ratios from litters sired by reciprocal cross F1 males (letting A represent a set of autosomes) are 0.510 from AH/AL, XL/YH and 0.469 from AH/AL, XH/YL. The difference is statistically significant but only half the difference between pure strains. The paternal effect, presumably due to the Y, persists in progeny of the two kinds of F2 males. In backcrosses to the female parent, resulting finally in AH/AH, XH/YL and AL/AL, XL/YH, and in outcrosses, the effect of the Y chromosome does not persist, indicating that neither the Y alone, nor the autosomes alone, will cause the sex ratio to depart significantly from equality of sexes. When pairs of males in all possible combinations were presented with C57BL/6 females mating success gave the following ranking: AH-YL, AL-YL, AH-YH, AL-YH. The combination of autosomes from PHH and Y-chromosome from PHL seems to confer the greatest competitive advantage.