Aamc 8 #131

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Jwinsler7

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This was a bio passage about different species of lizards and their dewlap (large skin fold that reflects UV light) under the throat. According to the passage, male lizards have this.

Q. If the lizards have X-Y chromosomal sex determination, the locus of a gene for the UV reflectance pigment:

A. must be on the X chromosome
B. must be on the Y chromosome
C. must be on an autosome
D. Could be a sex chromosome or on an autosome

I chose B since male lizards have this dewlap, and Y chromosome is passed from a father to its male offspring. So I thought the gene would have be to on the Y chromosome only. But the answer is D. Could anyone tell me why it could be on either x or y chromosome and also can be on an autosome? Thanks in advance.

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For the purpose of the MCAT all sex-linked traits are located on the X-chromosome. There are very very few exceptions but you almost definitely will never see these on an exam. And based on the information you gave, we cannot be sure if it is sex linked or not, meaning D is the correct answer.
 
It cannot be discounted that females also have the UV reflectance gene or that its on an autosome, even though it seems that only males have it.
 
It cannot be discounted that females also have the UV reflectance gene or that its on an autosome, even though it seems that only males have it.

This. I think the question purposely misleads you to think in terms of the dewlap, but it's really asking about the UV pigment.
 
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