Question

Red eyed plain thorax Drosophila flies were crossed with pink eyed, striped thorax flies. \(F_{1}\) generation flies were test crossed with recessive flies. \(F_{2}\) generation result is as follows. \[ \text{Red eyed plain thorax}=80 \] \[ \text{Red eyed striped thorax}=16 \] \[ \text{Pink eyed plain thorax}=12 \] \[ \text{Pink eyed striped thorax}=92 \] Find out the percentage of recombinants.

• A. \(12\%\)
• B. \(16\%\)
• C. \(14\%\)
• D. \(86\%\)

Hint:

In linkage problems, the largest classes are parental types and the smallest classes are recombinants. Use recombinants/total offspring × 100.

Answer 1

The Correct Option is C

Concept: In a test cross involving linked genes, parental combinations appear in higher frequency, whereas recombinant combinations occur in lower frequency. The recombination frequency is calculated as: \[ \text{Recombination Frequency} = \frac{\text{Number of Recombinants}}{\text{Total Offspring}} \times 100 \]

Step 1: Identify parental classes. The most frequent classes are: \[ 80 \; (\text{Red plain}) \] \[ 92 \; (\text{Pink striped}) \] These represent parental combinations.

Step 2: Identify recombinant classes. The less frequent classes are: \[ 16 \; (\text{Red striped}) \] \[ 12 \; (\text{Pink plain}) \] These represent recombinant combinations.

Step 3: Calculate total recombinants. \[ 16+12=28 \]

Step 4: Calculate total offspring. \[ 80+16+12+92=200 \]

Step 5: Calculate recombination percentage. \[ \text{RF} = \frac{28}{200}\times100 \] \[ =14\% \]

Step 6: Final conclusion. \[ \boxed{14\%} \] Hence option (C) is correct.