Question

You are studying three genes X, Y, and Z that are linked (in that order) in the Imperial Scorpion Pandinus imperator. The distance between X and Y is 10 cM, the distance between Y and Z is 8 cM. You conduct a testcross by crossing a heterozygous female with a homozygous recessive male and obtain 1500 testcross progeny. When the progeny are analyzed, you find five double crossover offspring. What is the interference value shown by this cross?

a) 0
b) 0.2
c) 0.4
d) 0.6

Answer 1

The interference value is calculated by determining the expected number of double crossovers and comparing it to the observed number. For the given scenario with the Imperial Scorpion, the interference value is approximately 0.6, so the correct answer is option (d).

Step-by-step explanation:

To calculate the interference value in a genetic cross, we need to understand the expected number of double crossovers and compare that to the observed number. Interference is a measure of how one crossover event can inhibit the occurrence of another crossover event nearby on a chromosome. It is calculated using the formula: Interference = 1 - (Observed Double Crossovers / Expected Double Crossovers).

The expected number of double crossovers can be calculated by multiplying the independent probabilities of a crossover in each interval: (Distance between X and Y in cM/100) * (Distance between Y and Z in cM/100) * Total Offspring. In the scenario provided, the expected number of double crossovers would be (10/100) * (8/100) * 1500 = 12.

Given that only five double crossovers were observed, we can now calculate the interference: Interference = 1 - (5 / 12) = 1 - 0.4167 = 0.5833. When rounded to one decimal place, the interference value is approximately 0.6. Therefore, the correct option is (d) 0.6.