In Drosophila, the genes b, c, and sp are linked and arranged as shown below: b--30 m.u.--c--20 m.u.--sp
This region exhibits 90% interference.How many double crossovers would be recovered in a three-point cross involving b, c, and sp out of 1000 progeny?
A)3
B)6
C)54
D)60
E)600

Question

Quizplus · Accepted Answer

Interference is the phenomenon where the occurrence of a crossover in one region of a chromosome inhibits the occurrence of another crossover nearby. With 90% interference, only 10% of the expected double crossovers occur. The expected double crossovers without considering interference can be calculated by multiplying the individual crossover frequencies: (30 m.u. * 20 m.u.) / 100^2 = 0.06 or 6%. Out of 1000 progeny, 6% would be 60. However, with 90% interference, only 10% of these 60 double crossovers are expected to occur, resulting in 6 double crossovers (60 * 0.1 = 6).

In Drosophila, the Genes B, C, and Sp Are Linked