What is the map distance between the A and B genes Genotypes

What is the map distance between the A and B genes?

Genotypes

Number

a

B

d

1

A

b

D

1

a

B

D

4

A

b

d

4

A

B

d

40

a

b

D

40

A

B

D

5

a

b

d

5

Total

100

Answers:

1 cM

5 cM

10 cM

12 cM

20 cM

I know the answer is 10 cM but could you explain the process of getting this answer?

Solution

In order to identify the distance between two alleles, the number of offsprings carrying both of these genes should be noted because these offpsrings will depict that these two genes are inherited together. This is because the parental class will show genotype with no-cross over events and represent the acutal gene distance between the alleles. From the tabulated data, it can be seen that only the organisms with genotypes ABD and abd represent the parental types with frequncies of 5 each. Thus, the parental types count to 5+5 or 10.

This gives the gene distance between them as:

(Number of offsprings with parental genotype 8 100 )/ total progeny size

or (10*100)/100 or 10cM