Parthenogenesis: Does It Occur Spontaneously in Mice?

If parthenogenesis occurred in bisexual organisms, it would produce an excess of females and depress the sex ratio. The phenotypes of female mice, from matings that produce an excess of females, were examined for evidence of the presence of marker genes of paternal origin. All proved to be hybrids of the maternal and paternal strains, thus excluding parthenogenesis as the cause of the low sex ratio.