Sex-related mortality in developing chicken (Gallus domesticus) embryos

A total of 528 fertilized chick eggs (including 48 nonfertile eggs) were examined for viability and chromosomal sex after 60 to 90 h of incubation. Of those that contained embryos, 196 were male (ZZ), 183 were female (ZW), and 101 were of undetermined sex. The embryonal mortality rate was 18% for both the homogametic and the heterogametic sex and 19% for the undetermined sex groups. The results are consistent with the hypothesis that the sex ratio among live embryos does not deviate from 50 % male during the early incubation period and that recessive sex-linked lethal genes do not contribute significantly to a difference in mortality between the sexes in an ordinary breeding flock. It is suggested that sexing early chick embryos by chromosome morphology may require relatively small samples to detect lethal recessives induced by potentially mutagenic agents.