Maternal age and the incidence of aneuploidy in first-cleavage mouse embryos.

Eggs obtained from young virgin and aged parous female mice were fertilized in vitro to compare the incidence of aneuploidy in the resulting first-cleavage embryos. There was a significantly higher incidence of aneuploidy in the aged group (7.5% versus 3.3%) and this was due solely to a higher proportion of trisomic female chromosome complements; there was no difference in the incidence of monosomics. These results thus suggest that non-disjunction occurs more frequently in eggs from older females, leading to the production of aneuploid embryos.