21. The distance between the B and C gene is the cross above is: a) 2 mu b) 4 mu

Question

21. The distance between the B and C gene is the cross above is: a) 2 mu b) 4 mu c) 10 mu d) 96 mue) None of the above The following four questions refer to the map below: 10 5 15 10 20 5 22. The distance between the A and G gene in map units (mu) is: a) 50 b) 65 c) 100 d) 130 e) None of the above 23. In the cross Ce/cE by ce/ce the fraction of the progeny that are CE is: a) 0.125 b) 0.25 c) 0.375 d) 0.5 e) 0.75 24. In the cross ABC/abc by abc/abc the fraction of the progeny that are ABc is: a) 0.0025 b) 0.005 c) 0.0225 d) 0.045 e) 0.075 25. For the cross Af/aF by af/af the fraction of progeny that are AF plus af is: a) 0.25 b) 0.3 c) 0.5 d) 0.6 e) 1.0

Explanation / Answer

22- As we can see that A and G genes are at the same point in the map. So correct answer is option E- None of the above.

23 - Map distance between C and E is 25. So maximum number of recombinants will be 25%. In this 25% recombinants, half will have CE and another half will have ce genotype. or 0.125 Ce and 0.125 ce.

So answer is option A - 0.125

24- It involves three genes so there will be a chance of double cross over.

If the cross involves only two genes then the maximum number of recombinant would have 5% or, half will have Bc and another half will have bC genotype. or 0.025 cB and 0.025 Cb. But due to the involvement of three genes, some of the progeny will be participating in the double crossover. So answer will be 0.0225

So answer is option C- 0.0225

25- In any case, the maximum number of recombinants can't be more than 50% even though the distance between the genes is more than 50 mu

So the answer will be 0.25 which is option A.

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