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Discus: SAT/ACT Tests and Test Preparation: May 2004 Archive: AP BIO QUESTION<<<
By Lahlahlah (Lahlahlah) on Sunday, May 09, 2004 - 03:05 pm: Edit

question from the 1990 ap bio test

"In fruit flies, vermilion eyes are a sex-linked receszsive characteristic. If a vermilion-eyed female is crossed with a wild type male, what proportion of the male offspring should have vermillion eyes?


The answer is E, 100%.

I'm wondering how do you tell what the genetic make-up of a "wild-type" male is?

If vermilion eyes are sex linked how can you have a wild type male? Isn't a wild type male one with both recessive and dominant alleles?


By Tanman (Tanman) on Sunday, May 09, 2004 - 03:11 pm: Edit

I think that all "wild type" means is the normal/common allele (as opposed to the "mutant" allele)

By Pianoman (Pianoman) on Sunday, May 09, 2004 - 03:12 pm: Edit

A wild type allele is the normal allele for a gene, and in this case the dominant version. Thus, you would carry out a cross like this: The female, Xr (r should be at the top) and Xr with wild type male XR(dominant) and Y (can't have anything on the Y). The gametes are XRXr, XRXr, XrY, and XrY. Thus the males, which have XY, both have the recessive characteristic and are 100% with vermillion eyes. Hope that helped in some way!

By Lahlahlah (Lahlahlah) on Sunday, May 09, 2004 - 03:25 pm: Edit

oh i see, why can't they just say dominant :P

By Aim78 (Aim78) on Sunday, May 09, 2004 - 03:36 pm: Edit

It's not necessarily dominant, it's just the normal trait that the majority have.

By Unluckycharms (Unluckycharms) on Sunday, May 09, 2004 - 03:45 pm: Edit

It wouldn't matter if the male had vermillion eyes or not. It would still come out to be 100%

By Firebird12637 (Firebird12637) on Sunday, May 09, 2004 - 03:47 pm: Edit

u dont even need to know what "wild" means...

if you have a vermillion eyed female, then u have XrXr, then the male is X(doesnt matter)Y

then all male offspring are of the form XrY, no matter what, so the answer is 100%

By Aim78 (Aim78) on Sunday, May 09, 2004 - 07:37 pm: Edit

Right, because you know if you're getting a male, then the sperm had only a Y chromosome.

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