The effect of synchronous and asynchronous egg transfer on foetal weight in mice selected for large and small body size.

The weight difference between large, small and unselected strains of mice were maintained when blastocysts of each genotype were transferred to unselected control recipients, suggesting that foetal genotype was an important factor in determining prenatal body size. The asynchronous transfer of large, small and unselected embryos resulted in a highly significant (P less than 0-001) elevation of foetal weight compared with synchronously transferred groups, genetically small mice attaining a foetal weight greater than the normal large strain. This result suggested that foetal genotype did not limit the capacity of each strain for prenatal growth. It is postulated that foetal genotype exercises its control over embryonic growth by affecting the state of embryonic development at implantation.