Question

A dihybrid AB/ab was testcrossed to a tester of genotype aabb. What will be the expected segregation ratio of testcrossed progeny if the A and B genes were 2% recombination apart on the chromosome?

Please explain how you got to the answer (don't just give the answer), I'm struggling to understand my teacher and would like to know the logic behind it. Thanks

Answer 1

Distance between two genes can be estimated with the help of Recombination frequency (RF).

Recombination frequency (in %) = (No. of recombinants / Total no. of progeny) * 100

Two genes are located 1 map units or 1 centi Morgan apart if they show 1% recombination frequency.

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Recombination frequency between genes A and B is 2%. Cross between AB / ab and ab/ab will give only 2% recombinant gametes and 98% parental gametes.

Ratio of gametes will be -

AB - 49% (parental)

ab - 49% (parental)

Ab - 1% (recobinant)

aB - 1% (recombinant)