Question

1.Use the following information for this question. The distances between genes A, B, C and D are A-B= 5 map units, B-C= 10 map units and C-D= 15 map units. The genes are arranged in the order -A-B-C-D- on the chromosome. What would be the expected percentage of progeny that has the genotype ABC/abc or abc/abc from the cross AbC/aBc X abc/abc?

2.The distance between genes A & B is 15 mu, the distance between genes B & C is 10 mu, the distance between A & C is 25 mu. For an individual with the genotype AbC/aBc, what proportion of ABC gametes would you predict?

Answer 1

1)

ABC/abc or abc/abc progeny would be produced from AbC/aBc individual when a double crossover occurs between the A-B and B-C loci. The expected frequency of double crossovers is the product of the two single crossover frequencies.

Expected double crossover frequency = Freq(A-B) * Freq (B-C) = 0.05 * 0.1 = 0.005

Thus, the expected frequency of double crossover gametes is 0.005 or 0.5%, and the expected frequency of the ABC/abc progeny is 0.25% and the expected frequency of the abc/abc progeny is also 0.25%.

2)

Expected frequency of double crossovers = Freq(AB) * Freq(BC) = 0.15 * 0.1 = 0.015

The expected frequency of ABC gametes is 1.5%