Sex-limited and sex-modified genetic defects in swine--cryptorchidism.

Review of published data suggests that cryptorchidism in Chester Whites and Yorkshires is caused by completely penetrant, recessive genes at two autosomal loci; in Lacombes, multifactorial modes of inheritance are more plausible. Different genetic systems control presence of the trait vs. number of sides affected; left testes are retained more often in almost all samples. Contrary to previous claims prenatal viability of homozygous males and females is normal. Genes causing cryptorchidism are unlikely to affect many other malformations in either sex, but pleiotropy is suggested to extend to economic traits such as conformation in females.