Variation in phenotype due to random intrauterine positioning of male and female fetuses in rodents

vom Saal, F. S.

As rodents are polytocous, male and female foetuses can develor in utero contiguous to foetuses of the same or opposite sex. This paper reviews experiments demonstrating that random intrauterine positioning of male and female foetuses results in within-sex variation in phenotype in mice and rats. This phenomenon provides a clear example of the degree to which the intrauterine environment can bias development in terms of effects or morphology, physiology and behaviour.