In the cross shown here, involving two linked genes, ebony (e) and claret (ca), in Drosophila, where crossing over does not occur in males, offspring were produced in a 2 + : 1 ca : 1 e phenotypic ratio: These genes are 30 units apart on chromosome III. What did crossing over in the female contribute to these phenotypes?

Key Concepts

Linked Genes

Linked genes are genes that are located close to each other on the same chromosome and tend to be inherited together during meiosis. Their proximity reduces the likelihood of recombination occurring between them, which can affect the phenotypic ratios observed in offspring. In the case of Drosophila, the genes ebony (e) and claret (ca) are linked, influencing the inheritance patterns seen in the cross.

Crossing Over

Crossing over is a genetic process that occurs during meiosis where homologous chromosomes exchange segments of genetic material. This recombination can create new allele combinations, leading to genetic diversity in the offspring. In the context of the question, crossing over in females contributes to the observed phenotypic ratios by allowing for the production of recombinant gametes, which can result in different combinations of the linked genes.

Genetic Mapping

Genetic mapping is a technique used to determine the relative positions of genes on a chromosome based on the frequency of recombination between them. The distance between genes is often measured in centimorgans (cM), with 1 cM corresponding to a 1% chance of recombination occurring. In this scenario, the genes ebony and claret are 30 units apart, indicating a moderate likelihood of crossing over, which affects the phenotypic ratios of the offspring.