In Drosophila the genes for withered wings whd smooth abdome

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.

(a) Calculate the number of expected double crossover progeny.Express your answer to the nearest whole number in the blank provided: (a) ____

(b) Assume that the interference for these genes is 0.3. Calculate the number of observed double crossover progeny. Express your answer to the nearest whole number in the blank provided: (b) ____

Solution

(a)The possibility of single crossover between genes whd and sm= 30.5/100=0.305

The possibility of single crossover between genes sm and sp= 15.5/100=0.155

Now, estimate the expected frequency for the occurrence of double crossover among these genes= 0.305x0.155=0.047275 or 0.047275x100=47.275 or 47 progeny will have double crossovers.

(2) They mentioned that interference is 0.3, means the observed crossovers will have 30% deviation from that of expected double crossovers.

In the previous question, we estimated the expected number of double cross over as 47.275.

When you have 30% interference, then oberved progeny with double cross over will be 47.275-(30x47.275/100)=47.275-14.2=33.1

Calculate the number of observed double crossover progeny=33