Tricky Genetics Question?

[JamieMac]

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Any thoughts on this one...

A colorblind male (XcY) is crossed with a normal female who is a carrier of fragile X disorder and colorblindness (XcCf). What is the probability that the child will be phenotypically normal?

Now I thought this was a trick question because "phenotypically" the colorblind male would appear normal, and of course the other male would have fragile X and physically exhibit these characteristics. Therefore I answered 50%. The answer, however, is 0%.

Am I wrong in thinking this?

 

[Streetwolf]

Any thoughts on this one...

A colorblind male (XcY) is crossed with a normal female who is a carrier of fragile X disorder and colorblindness (XcCf). What is the probability that the child will be phenotypically normal?

Now I thought this was a trick question because "phenotypically" the colorblind male would appear normal, and of course the other male would have fragile X and physically exhibit these characteristics. Therefore I answered 50%. The answer, however, is 0%.

Am I wrong in thinking this?

Yes you are. Genotypically normal means both genes are normal. Phenotypically normal means the mutation is not expressed. In this case the colorblind male would express the colorblind mutation.

It is possible for an organism to be normal phenotypically but not genotypically. This happens when they are heterozygous for a mutation and the mutation only expresses itself when it is recessive.

 

[JamieMac]

Thanks for the reply. It appears that my definition of "phenotype" was a bit skewed. I always thought that it denoted something that would only appear as a physical property (height, weight, hair color, etc.)