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'O' Level Heredity Question

Genetics as it applies to evolution, molecular biology, and medical aspects.

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'O' Level Heredity Question

Postby protomandaniel » Sun Nov 14, 2010 6:47 am

I was doing past year 'O' level papers and suddenly I discovered this ambiguous question. It was in 2007 paper.
Question 39
In mice, the allele for black fur colour is dominant to the allele for white fur colour.
What does this mean in a mouse population?
A. Mice with black fur are more successful breeders
B. Most mice have black fur
C. When a black-furred mouse breeds with a white-furred one, the offspring have grey fur
D. White furred mice are only born to two white-furred parents.

Most of my teachers and even the answer key in the papers book say the answer is B. But the answer is obviously wrong.
I mean, let's see the same thing from human: hair colour. One of the genes for hair colour has the dominant allele as black hair and recessive allele as blond hair. Yet we cannot say most people have black hair because it is dominant. There are people on Earth with black hair, brown hair, red hair and of course, a lot of people with blond hair.
Also, there are plenty of diseases conferred by dominant alleles, say, Huntington's and myotonic dystrophy. Yet not even one fourth of the world's population has Huntington.
Please enlighten me with the right answer to this question. Thanks.
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Postby JackBean » Sun Nov 14, 2010 9:30 am

well, then think about the other answers:
A) are black mice more successful, because they have dominant allele for coat color?

B) yeah, just becaue it's dominant doesn't mean it must be the most common one.

C) could be, but doesn't have to,think why and when

D) is this rigth? Which other combination could give white mice?
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Postby protomandaniel » Sun Nov 14, 2010 12:39 pm

You seem to think that the answer is D but two heterozygous black mice can give 25% white mice also. I also think it's D but I think its phrasing should be two white-furred parents can only give birth to white-furred mice.
How do you think about that? Anw, thanks, Jack.
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Postby JackBean » Mon Nov 15, 2010 8:52 am

Well, I was at first, but then I realized, that also other parents could have white furred offspring... seems like any answer is 100% correct :(
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Postby Mickey56 » Thu Aug 11, 2011 11:50 am

I agree with JackBean, none of the test answers is true to life. And the one your teacher suggested sounds more than strange. And what about grey and white mice? Exceptions?
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Re: 'O' Level Heredity Question

Postby Jenniestarlinks » Wed Oct 12, 2011 10:21 am

i think answer depends very much on how the question is phrased, the question is "In mice, the allele for black fur colour is dominant to the allele for white fur colour.
What does this mean in a mouse population?"
we have to consider only the condition that black fur is dominant and white is recessive , therefore C cannot be the answer to "this" question because nothing about codominane is mentioned in the question, D is totally incorrect as protomandaniel said, and then as jackbean said : are black mice more successful, only because they have dominant allele for coat color?therfore eliminate A...conclusively with trial and error method B seems to be the most suitable answer...
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