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A) Genes A, B, and C are linked as shown below. A and B are 10 m.u. apart, while

ID: 198250 • Letter: A

Question

A) Genes A, B, and C are linked as shown below. A and B are 10 m.u. apart, while B and C are 20 m.u. apart. All dominant alleles are on one homologue and all recessive alleles are on the other homologue. Which genotype and probability is correct for no crossing over?

B) Genes A, B, and C are linked as shown below. A and B are 10 m.u. apart, while B and C are 20 m.u. apart. All dominant alleles are on one homologue and all recessive alleles are on the other homologue. Out of 1,000 total offspring, you expect 20 offspring to come from a double crossover, but you observe only 15 offspring. What is the interference?

Explanation / Answer

A) Genes A, B, and C are linked as shown below. A and B are 10 m.u. apart, while B and C are 20 m.u. apart. All dominant alleles are on one homologue and all recessive alleles are on the other homologue. Which genotype and probability is correct for no crossing over?

It is given that the distance between A and B = 10 mu

And between B and C = 20 mu.

In any case there will be recombination between A and B, and Band C as they are very newr located.

So in this case there will be no crossing over between A and C because they are apart.

So for no crossing over the cross should be between

A/C x a/c

In this case genes are unlinked, so all four offsprings from the testcross (including a/a ; b/b) would equal 25 percent.

B) Genes A, B, and C are linked as shown below. A and B are 10 m.u. apart, while B and C are 20 m.u. apart. All dominant alleles are on one homologue and all recessive alleles are on the other homologue. Out of 1,000 total offspring, you expect 20 offspring to come from a double crossover, but you observe only 15 offspring. What is the interference?

Interference = 1- coincidence

And coefficient of Coincidence = observed double recombinants/expected double recombinants

= 15/20= 0.75

So interference = 1-0.75 = 0.25.

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