What is the expected phenotypic ratio of the offspring when a triple heterozygot

Question

What is the expected phenotypic ratio of the offspring when a triple heterozygote in coupling is testcrossed, assuming the genes are linked and no crossing over occurs. ? 9:33 1 O Impossible to predict QUESTION 30 Gene A is 10 mU from Gene B on chromosome 2, and the alleles are in coupling. An individual with the genotype AaBb is testcrossed. What fraction of the offspring would be expected to have genotype aabb? O 10% of the offspring O 20% of the offspring 30% of the offspring O 45% of the offspring none of the answers are correct

Explanation / Answer

On crossing a triplet heterozygote with test organism , say AaBbCc×aabbcc,

There are 3 gene pairs , and second parent is homozygous recessive.

No. Of phenotypes = 2^n

Here , n=3 (gene pairs )

So 2^3=2×2×2

=8

So ratio required will be 1:1:1:1:1:1:1:1 (all Phenotype with equal probability).

Ans 29:

Given that the two genes are 10mU apart.

So there will be 10% recombinant and 90% parental types.

Parents are AaBb × aabb

Thus , in progeny out of 90% , half will be AaBb and half will be aabb.

=1/2 × 90

=45% of the offspring.

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