In Drosophila subobscura, the presence of a recessive gene called grandchildless (gs) causes the offspring of homozygous females, but not those of homozygous males, to be sterile. Can you offer an explanation as to why females and not males are affected by the mutant gene?

Key Concepts

Sex-Linked Inheritance

Sex-linked inheritance refers to genes located on sex chromosomes, which can lead to different expressions of traits in males and females. In Drosophila, males have one X and one Y chromosome, while females have two X chromosomes. This difference can result in certain traits, like the grandchildless gene, being expressed differently based on the sex of the individual.

Recessive Genes

Recessive genes require two copies (homozygous) to express their traits, meaning that a recessive trait will only manifest in individuals with two recessive alleles. In the case of the grandchildless gene, homozygous females (gs/gs) express sterility, while males with only one recessive allele (gs/Y) do not show the trait, as the Y chromosome does not carry the gene.

Gene Interaction and Dosage Compensation

Gene interaction refers to how different genes and their alleles influence each other's expression. In Drosophila, dosage compensation mechanisms equalize the expression of X-linked genes between males and females. This means that the presence of the grandchildless gene in females leads to a direct impact on fertility, while males, having only one X chromosome, do not experience the same effect due to the lack of a second allele.