The maternal-effect mutation bicoid (bcd) is recessive. In the absence of the bicoid protein product, embryogenesis is not completed. Consider a cross between a female heterozygous for the bicoid alleles (bcd⁺/bcd⁻) and a male homozygous for the mutation (bcd⁻/bcd⁻).

Predict the outcome (normal vs. failed embryogenesis) in the F₁ and F₂ generations of the cross described.

Key Concepts

Maternal-effect genes

Maternal-effect genes are genes expressed in the mother that influence the phenotype of the offspring, regardless of the offspring's own genotype. In the case of bicoid, the mother's genotype determines the presence of the bicoid protein in the egg, which is crucial for proper embryonic development. If the mother is heterozygous for the bicoid alleles, she can produce bicoid protein, affecting the embryos' development.

Recessive alleles

Recessive alleles are variants of a gene that do not manifest in the phenotype unless two copies are present. In this scenario, the bicoid mutation (bcd⁻) is recessive, meaning that only embryos with two copies of the bcd⁻ allele will exhibit failed embryogenesis. Heterozygous individuals (bcd⁺/bcd⁻) will show normal development due to the presence of the dominant bcd⁺ allele.

Punnett square and inheritance patterns

A Punnett square is a tool used to predict the genotypes of offspring from a genetic cross. By analyzing the genotypes of the parents (bcd⁺/bcd⁻ and bcd⁻/bcd⁻), one can determine the expected genotypic and phenotypic ratios in the F₁ and F₂ generations. This method helps in understanding how traits are inherited and the likelihood of offspring exhibiting certain phenotypes based on parental genotypes.