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.

In your experimental design, what are the genotype and phenotype of the line you propose to cross to the F₁ to obtain the most useful information about genetic linkage between the eye color and bristle-length genes? Explain why you make this choice.

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. This phenomenon can affect the assortment of alleles and can be measured by the frequency of recombination events. Understanding linkage is crucial for predicting the inheritance patterns of traits, as linked genes do not assort independently, which can lead to deviations from Mendelian ratios in offspring.

Drosophila Genetics

Drosophila melanogaster, commonly known as the fruit fly, is a model organism widely used in genetic studies due to its simple genetic structure, short life cycle, and ease of breeding. In this context, the specific traits of eye color and bristle length are controlled by alleles that can be dominant or recessive. Familiarity with Drosophila genetics, including the notation for dominant (c⁺, d⁺) and recessive (c, d) alleles, is essential for designing experiments and interpreting results.

Experimental Design in Genetics

Experimental design in genetics involves planning a controlled experiment to test hypotheses about inheritance patterns. In this case, crossing a homozygous red-eyed, short-bristled Drosophila with a brown-eyed, long-bristled counterpart will produce F₁ offspring that are heterozygous for both traits. Analyzing the phenotypes of the F₂ generation will provide insights into whether the genes for eye color and bristle length are linked, based on the expected ratios of phenotypes.