First slide
Inheritance of Two Genes
Question

A heterozygous individual ++/ab is crossed to its recessive parent and has produced the offsprings in following proportion 

++/ab – 200
a+/ab – 50
+b/ab – 30
ab/ab – 100

What is the expected distance between the two gene loci?

Moderate
Solution

When a heterozygous individual ++/ab is crossed to its recessive parent, the offspring with the following genotypes are formed.

Parental genotypes - ++/ab – 200
Recombinant genotypes - a+/ab – 50
Recombinant genotypes - +b/ab – 30
Parental genotypes - ab/ab – 100

Recombination frequency =  Number of recombinants (80)Total number of off spring(380) X 100 = 21 % 

Distance between gene a and gene b is 21cM.

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