[ **up: [[Mammals]] | [[Reproduction and sex]]** ] --- # Intrauterine position (Effect on litter-bearing mammals) [[2025-0316. 'The intrauterine position relative to members of the same or opposite sex has profound effects on the reproductive life history in many litter-bearing mammals.'|'The intrauterine position relative to members of the same or opposite sex has profound effects on the reproductive life history in many litter-bearing mammals.']][^1] [[2025-0316. 'The intrauterine position relative to members of the same or opposite sex has profound effects on the reproductive life history in many litter-bearing mammals.'|’Sex chromosome segregation in XY* females produce a 1 male:2 females sex ratio since YY* zygotes are lost early; this increases the probability that a female embryo could be gestated between two female embryos. … For instance, in the Mongolian gerbil (Meriones unguiculatus) female fetuses gestated between two female fetuses (2F females) are early-maturing and have a grater lifetime fecundity than 2M females (those gestated between two male fetuses).’]][^2] [^1]: M. B. Espinosa and A. D. Vitullo, ‘[[Espinosa & Vitullo. ‘Offspring sex-ratio and reproductive performance in heterogametic females of the South American field mouse Akodon azarae’, 1996.|Offspring sex-ratio and reproductive performance in heterogametic females of the South American field mouse Akodon azarae]]’, *Hereditas* 124 (1996), p. 61. [^2]:M. B. Espinosa and A. D. Vitullo, ‘[[Espinosa & Vitullo. ‘Offspring sex-ratio and reproductive performance in heterogametic females of the South American field mouse Akodon azarae’, 1996.|Offspring sex-ratio and reproductive performance in heterogametic females of the South American field mouse Akodon azarae]]’, *Hereditas* 124 (1996), p. 61.