Two different genes are located on the same chromosome but t

Two different genes are located on the same chromosome, but their exact position in not known. Individual 1 and 2 have the genotypes shown below. The parallel lines represent homologous chromosomes.

Individual #1:

A B
____

a b

Individual #2:

a b

____

a b

How likely is it that these individuals will have an offspring with the following genotype:

A b

_____

a b

A.More likely if the two genes are close together on the chromosome

B.More likely if the two genes are far apart on the chromosome

C.Equally likely no matter where the genes are located on the chromosome

Solution

So, the genotypes are AB/ab and ab/ab for the individuals 1 & 2, respectively. Assuming that there is no recombination, gametes from AB and ab from individual 1. All gametes from individual 2 will have genotype ab.

If offspring should have Ab/ab genotype, it is possible only if recombination occurs between both genes in individual 1.

So, the correct answer is B. Recombination frequency is proportional to the physical distance between the genes. The farther the genes on chromosome, more is the chance of a recombination between the genes.

Recombination takes place during crossing over. Crossing over requires formation of chiasma. Formation of chiasma is easily possible when the distance between two genes is more.