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AAMC Full Length Test 1 - Biological Section Stand-Alone
Saloni_5218
#1 Posted : Saturday, July 18, 2020 1:24:07 AM
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Hi,

I am not sure if I am allowed to ask questions about the AAMC Full Length Tests or not but I need some clarity on it.

So the Stand-Alone question was,

"Assume that K and M are two unlinked genes that affect hearing. The dominant K allele is necessary for hearing, and the dominant M allele causes deafness regardless of the other genes present. Given this, what fraction of the offspring of parents with the genotypes KkMm and Kkmm will most likely be deaf?"

The answer choices were:

A) 1/4
B) 3/8
C) 1/2
D) 5/8

I chose C and got the question wrong.

The explanation they gave was,

"The answer to this question is D, because among the offspring of KkMm and Kkmm parents, the ones who lack a dominant K allele (necessary for hearing), or carry a dominant M allele (causes deafness) are deaf. Based on the Punnett square analysis, 10 out of 16 or 5/8 of all offspring are likely to be deaf."

How is it possible for a cross between the genotypes of KkMm and Kkmm to have a total of 16 offsprings...shouldn't the total be 8 offsprings?

And so how is the answer D?

The question also mentioned that "dominant M allele causes deafness regardless of the other genes"...so it shouldn't matter if the offsprings genotype had KK, Kk, or kk right...because that is how I got answer C?

I am not sure where my reasoning is off...does it have something to do with the fact that both genes are unlinked?

Thank You!
INSTR_Katerina_102
#2 Posted : Saturday, July 18, 2020 5:13:59 PM
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Hi,

This is a drawing of how the cross would go: https://ibb.co/yVQ9LXx

Because you have a punnett square with two traits, you will have 16 offspring (1/2)*4 = 1/16

The trick to this question is that you have two genotypic conditions for deafness:

1. If there is no K in the genotype, the offspring will be deaf (kk__ = deaf).

2. If there is an M in the genotype, the offspring will be deaf (__M_ = deaf)

I hope this helps!

Katt
Saloni_5218
#3 Posted : Sunday, July 19, 2020 1:26:54 AM
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Thank you!
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