(2.1): Drosophila melanogaster females heterozygous for three linked autosomal g

Question

(2.1): Drosophila melanogaster females heterozygous for three linked autosomal genes (a,b, and c) are testcrossed with triple homozygous recessive males. The map distances are a-b 10 map units, b-c 20 map units, a-c 30 map unit, and the genes are in coupling, that is: all the recessive genes are on the same chromosome. Answer the following questions:

a. What percentage of the testcross progeny are genotype ab/ab?

b. What percentage of the testcross progeny are genotype Ac/ac?

c. What percentage of the testcross progeny are genotype bC/bc?

Explanation / Answer

Parental offspring are - 72% Single Crossover (b-c) - 18% Single Crossover (a-b) - 8% Double Crossover - 2% The a-b distance on the chromosome = 18% + 2% = 20% = 20 map units. The b-c distance on the chromosome = 8% + 2% = 10% = 10 map units. The a-c distance on the chromosome = 20% + 10% = 30% = 30 map units. Hope this information helps you in calculating the percentages. All the best.

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