Question

In the Chinese primrose, the alleles A and a result in blue-colored versus slate-colored flowers, B and b in green vs. red stigma, and C and c in short vs. long style. All 3 genes involved are on the same chromosome. A pure-breeding blue-colored, green-stigma, short-style strain was crossed to a pure-breeding slate-colored, red-stigma, long-style strain. The heterozygous F1 strain was testcrossed to a triply homozygous recessive strain. The progeny are as follows:

Flower Stigma Style Number of progeny
blue green long 14
blue green short 224
slate green long 142
slate green short 118
slate red long 226
blue red long 122
slate red short 16
blue red short 138
What is the value for interference?
a) 0.36
b) 0.48
c) 0.65
d) 0.78

Answer 1

The value for interference in the given genetic cross of the Chinese primrose is calculated to be approximately 0.36, which is found by comparing the observed double crossover progeny with the expected number based on single crossover frequencies. The correct option is a.

Step-by-step explanation:

To calculate interference, we need to determine the expected number of double crossover (DCO) progeny based on the single crossover (SCO) frequencies and compare this to the observed number of DCO progeny. The formula for calculating interference (I) is I = 1 - (observed DCO / expected DCO).

First, we identify the single crossover frequencies from the given progeny data:
SCO between A and B: (blue green short) + (slate green long) = 224 + 142 = 366.
SCO between B and C: (slate red long) + (slate red short) = 226 + 16 = 242.

Next, the observed number of DCO is the sum of progeny with recombination in both regions: (blue red long) + (blue red short) = 122 + 138 = 260.

The expected number of DCO is the product of the probabilities of SCO between A and B and SCO between B and C, multiplied by the total progeny:
(366/676) × (242/676) × 676 = 366 × 242 / 676 ≈ 130.97.

Now we apply the interference formula:
I = 1 - (observed DCO / expected DCO) = 1 - (260 / 130.97) ≈ 0.36.

The value for interference is 0.36 (option a).