Question

Multiple choice:

The measured distance between genes D and E in a two-point testcross is 50 map units. Where are genes D and E in relation to each other?

1. D and E are on different homologous chromosomes.
2. D and E are on the same chromosome, at least 50 map units apart.
3. D and E are on the same chromosome, exactly 50 map units apart.
4. D and E are on the same chromosome, less than 50 map units apart.

A) 1 and 2

B) 1 and 3

C) 1 and 4

D) 2 and 3

E) 2 and 4

F) 3 and 4

Answer 1

Answer: “A” 1 and 2 i.e. D and E are on different homologous chromosomes or D and E are on the same chromosome atleaset 50 map units apart.

Explanation: one map unit signifies 1% recombination frequency(crossing over) which means the genes are very close to each other on the same chromosome, as the recombination frequency goes on increasing it can be said that the genes are far away from each other and hence the chances of the genes being not linked and not showing parental combination are higher.

Or if the recombination frequency is close to 50%, it can be said that the genes are present on different chromosomes and hence they are assorting independently.

The maximum distance the genes can be apart and still, the distance can be measured is 50 map units. If the recombination frequency is more than 50% , the predictions about the location of the genes can not be made. In this case the genes could be on the same chromosome atleast 50 map units apart or they could be present on different homologous chromosomes.