In Drosophila , the genes for withered wings ( whd ), smooth abdomen ( sm ) and
ID: 52215 • Letter: I
Question
In Drosophila, the genes for withered wings (whd), smooth abdomen (sm) and speck body (sp) are located on chromosome 2 and are separated by the following map distances:
whd ----------(30.5)----------sm-----(15.5)-----sp
A female with withered wings and a smooth abdomen was mated to a male with a speck body.
The resulting phenotypically wild-type females were mated with males that had the mutant phenotype for all three traits, producing 1000 offspring.
assume that the interference for these genes is 0.3
1. How many offspring are expected to have the following phenotypes?
withered wings, speck body
OR
smooth abdomen
2. How many offspring are expected to have the following phenotypes?
withered wings, speck body, smooth abdomen
OR
wild type
3. How many offspring are expected to have the following phenotypes?
withered wings, smooth abdomen
OR
speck body
Explanation / Answer
The observed values of offspring are as follows:
1. Withered wings and speck body or smooth abdomen phenotypes occur with single cross overs between the whd and sm genes. Based on recombination frequency, the expected number of offspring are 272
2. The phenotype withered wings, smooth abdomen and speck body; or wild type results from a single cross over between sm and sp genes. The expected number of progeny is 122.
3. The phenotype withered wings and smooth abdomen, speck body are wild type or parentals. The expected number of progeny is 573.