Cell number in relation to heterosis during embryonic growth of mice

Abstract

Body and liver weight and the number of nuclei in the liver were significantly higher in F₁ hybrid than in inbred embryos developing in the same uterus after artificial heterospermic insemination. The size of 13-day-old F₁ hybrids corresponds to the size of 13·4-day in bred embryos. No significant differences in cell size were found between F₁ hybrid and inbred embryos of the same age. It is concluded that in 13–15-day embryos heterosis takes place through increase in cell number and not cell size.