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ACER Pink Booklet, Sec 3, Q54-56

ACER Pink Booklet, Sec 3, Q54-56

Postby matildamar1848 » Sat Jun 06, 2020 9:34 am


I have watched the gold standard videos for this test (thanks very much for all that hard work!), but I'm still a bit confused by this unit. Specifically, I'm wondering why your punnett squares were so small. For example, in Q55 why doesn't the table include Rb, rB, RB and rb? Is this because in the question stem it says that no crossing over occurs in males (so only the parental configuration is possible)?

Thanks again for all your fabulous resources :)
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Re: ACER Pink Booklet, Sec 3, Q54-56

Postby Benjalyn » Mon Jun 08, 2020 12:34 pm

Genes on the same chromosome that are in close proximity are often inherited together, meaning that while this question involved 2 genes, it is easier to solve than it appears. The confusing part in this question is the 50% recombination in the females, which means that 50% of the time the genes are not inherited together in the females and they in fact crossover. However, this is actually solvable with a simple punnett square, as the male genes are both Rb. This means that regardless of recombination in the female the outcome in the offspring will be the same.

This is shown in the extended punnett square below which accounts for the recombination: (please see document for the tables: ... sp=sharing)

The answer is D.

*Note that with different combinations of male genotypes or different percentages of recombination, an extended punnett square is required.
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