Recessive Mutations in Maternal-Effect Genes are Expressed Only in Embryos

Question

Recessive mutations in maternal-effect genes are expressed only in embryos produced by
A) females homozygous for the mutation.
B) females heterozygous for the mutation.
C) males homozygous for the mutation.
D) males heterozygous for the mutation.
E) None of these are correct.

Accepted Answer

Maternal-effect genes are expressed in the female gamete (egg) and affect early embryonic development. If a female is homozygous for a recessive mutation in a maternal-effect gene, all of her eggs will carry the mutation. Therefore, only the embryos produced by this female will show the phenotype associated with the mutation. Embryos produced by females heterozygous for the mutation will not show the phenotype because normal gene product from the wild-type allele can complement the mutant allele. Mutations in maternal-effect genes are not expressed in males because they do not contribute to the development of the embryo.