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?

Verified step by step guidance

1. <span>Understand the genetic basis of the grandchildless (gs) gene: It is a recessive gene, meaning that two copies of the gene (homozygous) are needed for the trait to be expressed.</span>
2. <span>Consider the inheritance pattern: Since the gene is recessive, only individuals with two gs alleles (gs/gs) will show the trait, which in this case is sterility.</span>
3. <span>Analyze the effect on females: Homozygous females (gs/gs) will produce eggs that carry the gs allele. If these eggs are fertilized, the resulting offspring will inherit the gs allele from their mother.</span>
4. <span>Consider the role of maternal effect: The grandchildless gene may have a maternal effect, where the phenotype of the offspring is determined by the genotype of the mother. This means that the presence of the gs allele in the mother affects the development of her offspring, leading to their sterility.</span>
5. <span>Explain why males are not affected: Homozygous males (gs/gs) do not pass on the maternal effect to their offspring, as they do not contribute to the cytoplasmic environment of the egg. Therefore, their offspring are not sterile.</span>

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.