Q3TYU - Campbell Biology

Question

A wild-type fly (heterozygous for gray body and normal wings) is mated with a black fly with vestigial wings. The offspring have the following phenotypic distribution: wild type, 778; black vestigial; 785; black normal, 158; gray vestigial, 162. What is the recombination frequency between these genes for the body color and wing size? Is this consistent with the results of the experiment in Figure 15.9?

Step-by-Step Solution

Answer

17% of recombination exists between the genes for the body color and wing size.

Yes, the recombination frequency is consistent with the experiment results, as the recombination frequency obtained in the experiment was also 17%. 

Step 1: Recombination frequency

The measure of recombinant offspring obtained in a genetic cross concerning the number of offspring produced is called recombination frequency. The recombination frequency between gene pairs helps to calculate the distance between the genes on a chromosome.

The following formula calculates the recombination frequency between gene pairs:\({\rm{Recombination frequency}}\,{\rm{ = }}\frac{{{\rm{Number of recombinants}}}}{{{\rm{Total number of offsprings}}}}\,{\rm{ \times 100}}\)

Step 2: Recombination frequency between genes for the body color and wing size

Four types of offspring were obtained from the cross. These were wild type, black vestigial, black normal, and gray vestigial. Wild type and black vestigial are wild type offspring, while black normal and gray vestigial are recombinants obtained from the cross.

The total number of offspring produced in the cross is \({\rm{778 + 785 + 158 + 162 = 1883}}\).

The total number of recombinants is \({\rm{162 + 158 = 320}}\).

The recombination frequency is calculated by substituting the values into the following equation: 

\({\rm{Recombination frequency}}\,{\rm{ = }}\frac{{320}}{{1883}}\,{\rm{ \times 100}}\)

\(\begin{aligned}{l}{\rm{Recombination frequency}}\, = \,16.99\,\% \\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \approx 17\% \end{aligned}\)

Thus, the recombination frequency between the genes for the body color and wing size is approximately 17%.

Step 3: Explanation for consistency with the experiment result

In the testcross performed in the experiment, between the body color and wing size, the recombination frequency obtained was 17%. It is consistent with the result of the cross here, as the recombination frequency obtained is also 17%.

The consistency is expected because the same genes were considered in both the experiment and the cross. The distance between the genes does not change from one cross to the other.