The boss in your laboratory has just heard of a proposal by another laboratory that genes for eye color and the length of body bristles may be linked in Drosophila. Your lab has numerous pure-breeding stocks of Drosophila that could be used to verify or refute genetic linkage. In Drosophila, red eyes (c⁺) are dominant to brown eyes (c) and long bristles (d⁺) are dominant to short bristles (d). Your lab boss asks you to design an experiment to test the genetic linkage of eye color and bristle-length genes, and to begin by crossing a pure-breeding line homozygous for red eyes and short bristles to a pure-breeding line that has brown eyes and long bristles.

How would the results of the cross differ if the genes are not linked?

Key Concepts

Genetic Linkage

Genetic linkage refers to the tendency of genes located close to each other on the same chromosome to be inherited together during meiosis. When genes are linked, the assortment of alleles does not follow the independent assortment principle, leading to a lower frequency of recombinant offspring. Understanding linkage is crucial for predicting the outcomes of genetic crosses and interpreting the results of experiments designed to test these relationships.

Drosophila Genetics

Drosophila melanogaster, commonly known as the fruit fly, is a model organism in genetics due to its simple genetic structure, short life cycle, and ease of breeding. In this context, traits such as eye color and bristle length are used to study inheritance patterns. The dominance relationships (red eyes dominant to brown and long bristles dominant to short) are essential for predicting phenotypic ratios in offspring resulting from specific crosses.

Punnett Square

A Punnett square is a diagram used to predict the genotypic and phenotypic outcomes of a genetic cross. By organizing the alleles from each parent, it allows for a visual representation of possible combinations in the offspring. In the context of the experiment, using a Punnett square will help determine the expected ratios of red-eyed, short-bristled offspring versus the alternative phenotypes, providing insight into whether the genes are linked or assort independently.