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A female fly is heterozygous for three X-linked genes. The dominant alleles are ABC and the recessive alleles are abc. She is crossed with an abc/Y male. The following progeny phenotypes are produced. These phenotypes are equally divided between male and female flies. Abc 420 aBC 435 abc 55 ABC 60 abC 14 ABc 16 Approximately how many double crossovers progeny would you have expected to see in the total of 1,000?

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Answer:

(14+16)/1000 *100= 3

Explanation:

Parental combinations are always more common then other recombinant progenies.

A female fly is heterozygous for three X-linked genes crossed with an abc/Y male. . If single crossover occurs between a & b  and between b & c, then the double cross is that, which occurs in both.

Double cross over progeny are always least in number, so here double cross occurs are in abC 14 and ABc 16.

So we are expecting that number of double cross over progeny= (14+16)/1000 *100= 3

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