Two genes a and b are linked in a dihybrid cross involving these two genes the f1 heterozygote is crossed with homozygous
recessive parental type aa bb what would be the ratio of offspring in the next generation
a 1 1 1 1 b 9 3 3 1 c 31 d 11

Question

Two genes ‘A’ and ‘B’ are linked. In a dihybrid cross involving these two genes, the F1 heterozygote is crossed with homozygous recessive parental type (aa bb). What would be the ratio of offspring in the next generation?
(a) 1 : 1 : 1: 1 (b) 9 : 3 : 3 : 1 (c) 3:1 (d) 1:1

Mr Stewart Payne · Answer

In a cross between a heterozygote for two linked genes (AaBb) and a homozygous recessive individual (aabb), we are looking at a test cross scenario. Since the genes are linked, they do not independently assort; instead, they are inherited together more frequently than not.

When the heterozygote (AaBb) is crossed with the homozygous recessive (aabb), the expectation is that there would be two parental types and two recombinant types. However, the parental types will be much more frequent because the genes are linked.

The possible offspring will be:

Ab (parental type)
aB (parental type)
AB (recombinant type)
ab (recombinant type)

If the linkage is very close, the recombinant types (AB and ab) will be much less frequent compared to the parental types (Ab and aB). Still, the simplest assumption for this test cross where linkage is not absolute but significant would still yield a 1:1:1:1 ratio, accounting for the parental and recombinant phenotypes.

Thus, the correct answer would be:

(a) 1 : 1 : 1 : 1

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