Stage of action of the litter-size effect on absence of otoliths in mice

Summary

The penetrance of absence of otoliths in pallid mice depends on the size of the litter in which an individual is born. An experiment is described which was designed to show whether the number of ova shed or of implantations, on the one hand, or the number of foetuses surviving from implantation to birth, on the other hand, was the important factor in this effect. This was done by comparing the offspring of normal mice with those of translocation heterozygotes, half of whose offspring die soon after implantation. The offspring of the two groups differed in mean otolith number by 0.74 units. It is concluded that the number of foetuses surviving after implantation was the major factor in the effect of litter-size on otolith formation in pallid mice.