In Drosophila, a female fly is heterozygous for three mutations, Bar eyes (B), miniature wings (m), and ebony body (e). Note that Bar is a dominant mutation. The fly is crossed to a male with normal eyes, miniature wings, and ebony body. The results of the cross are as follows.111 miniature 101 Bar, ebony29 wild type 31 Bar, miniature, ebony117 Bar 35 ebony26 Bar, miniature 115 miniature, ebonyInterpret the results of this cross. If you conclude that linkage is involved between any of the genes, determine the map distance(s) between them.

Verified step by step guidance

1. Identify the genotypes of the parents: The female is heterozygous for Bar (B), miniature (m), and ebony (e), so her genotype is BmE/bme. The male is homozygous recessive for all traits, so his genotype is bme/bme.
2. List the phenotypes and their corresponding genotypes: Bar (B-), miniature (mm), ebony (ee), and wild type (bme).
3. Determine the parental and recombinant phenotypes: Parental phenotypes are those that match the original parents, while recombinant phenotypes are new combinations of traits.
4. Calculate the recombination frequency: Use the formula (number of recombinant offspring / total number of offspring) x 100 to find the recombination frequency for each pair of genes.
5. Determine the map distances: The recombination frequency is equivalent to the map distance in centimorgans (cM). Calculate the map distances between each pair of genes based on the recombination frequencies.

Key Concepts

Genetic Linkage

Genetic linkage refers to the tendency of genes located close to each other on a chromosome to be inherited together during meiosis. This phenomenon occurs because linked genes are less likely to be separated by recombination events. Understanding linkage is crucial for interpreting genetic crosses, as it can affect the expected ratios of offspring phenotypes.

Map Distance

Map distance is a measure of the relative distance between genes on a chromosome, typically expressed in centimorgans (cM). It is calculated based on the frequency of recombination events between genes during meiosis. A higher map distance indicates a greater likelihood of recombination, suggesting that the genes are further apart on the chromosome.

Phenotypic Ratios

Phenotypic ratios represent the relative frequencies of different observable traits in the offspring resulting from a genetic cross. These ratios can provide insights into the inheritance patterns of traits, including dominance, recessiveness, and linkage. Analyzing the observed phenotypic ratios helps in determining whether the genes assort independently or are linked.