In Drosophila, Dichaete (D) is a mutation on chromosome III with a dominant effect on wing shape. It is lethal when homozygous. The genes ebony body (e) and pink eye (p) are recessive mutations on chromosome III. Flies from a Dichaete stock were crossed to homozygous ebony, pink flies, and the F₁ progeny, with a Dichaete phenotype, were backcrossed to the ebony, pink homozygotes. Using the results of this backcross shown in the table, Phenotype Number Dichaete 401 ebony, pink 389 Dichaete, ebony 84 pink 96 Dichaete, pink 2 ebony 3 Dichaete, ebony, pink 12 wild type 13 What is the sequence and interlocus distance between these three genes?

Key Concepts

Gene Linkage

Gene linkage refers to the tendency of genes located close to each other on the same chromosome to be inherited together during meiosis. This phenomenon affects the assortment of alleles and can lead to non-Mendelian ratios in offspring. Understanding gene linkage is crucial for analyzing the inheritance patterns observed in the Drosophila backcross results.

Recombination Frequency

Recombination frequency is a measure of the likelihood that two genes will be separated during meiosis due to crossing over. It is calculated by dividing the number of recombinant offspring by the total number of offspring. This frequency is used to estimate the genetic distance between genes, which is expressed in map units or centimorgans (cM).

Phenotypic Ratios

Phenotypic ratios represent the relative frequencies of different phenotypes observed in the offspring of a genetic cross. In this case, the ratios derived from the backcross data provide insights into the inheritance patterns of the Dichaete, ebony, and pink genes. Analyzing these ratios helps in determining the linkage relationships and distances between the genes.