The bicoid gene is a coordinate maternal–effect gene.A female that is homozygous for a loss-of-function bicoid allele is mated to a wild-type male. What are the phenotypes of their progeny?

Verified step by step guidance

1. Understand the concept of a maternal-effect gene: Maternal-effect genes are genes whose products (mRNA or proteins) are deposited into the egg by the mother and are essential for early embryonic development. The phenotype of the offspring is determined by the genotype of the mother, not the offspring's own genotype.
2. Identify the genotype of the mother: The mother is homozygous for a loss-of-function bicoid allele. This means she cannot produce functional bicoid protein, which is critical for establishing the anterior-posterior axis in the embryo.
3. Identify the genotype of the father: The father is wild-type, meaning he has a functional bicoid allele. However, since bicoid is a maternal-effect gene, the father's genotype does not influence the phenotype of the progeny in this case.
4. Determine the phenotype of the progeny: Since the mother cannot produce functional bicoid protein, the embryos will lack the bicoid protein necessary for proper anterior development. As a result, the progeny will exhibit a phenotype where the anterior structures (e.g., head and thorax) fail to develop properly, regardless of their own genotype.
5. Conclude that the progeny’s phenotype is determined solely by the mother’s inability to provide functional bicoid protein, leading to defective anterior development in all offspring.

Key Concepts

Maternal Effect Genes

Maternal effect genes are genes expressed in the mother that produce products (like mRNA or proteins) which are deposited into the egg. These products influence the development of the offspring, regardless of the offspring's own genotype. In the case of the bicoid gene, it plays a crucial role in establishing the anterior-posterior axis in the embryo.

Bicoid Gene Function

The bicoid gene is essential for proper embryonic development in Drosophila (fruit flies). It encodes a transcription factor that is crucial for the formation of the anterior structures of the embryo. A loss-of-function mutation in the bicoid gene results in embryos that lack head and thoracic structures, leading to severe developmental defects.

Homozygous Loss-of-Function Alleles

A homozygous loss-of-function allele means that both copies of a gene in an organism are non-functional due to mutations. In the context of the bicoid gene, a female that is homozygous for a loss-of-function allele will not produce functional bicoid protein, leading to progeny that are likely to exhibit severe developmental abnormalities, as they will not receive the necessary maternal bicoid products.