Genetics question

[Pdentalstudent]

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Hey guys, I don't quite understand the answer for this one.

If a male hemophiliac (X^hY) is crossed with a female carrier of both color blindness and hemophilia (X^cX^h) what is the probability that a female child be phenotypically normal?

The answer is 50%

But I don't get quite it because after doing the cross I get X^cX^h and X^hX^h and aren't both of these seen phenotypically? Or is it because the alleles are recessive and requires to have 2 in order to be seen phenotypically? :S

thanks in advance

 

[jefff]

yep you got it! 👍

1/2 X^c X^h - phenotypically normal
-----would need to be either X^cX^c or X^hX^h to be either color blind or hemophiliac respectively
**note X^c X^h is clearly a carrier for both the color blind and hemophilia alleles

1/2 X^h X^h - phenotypic hemophiliac

therefore 1/2 are phenotypically normal

Hey guys, I don't quite understand the answer for this one.

If a male hemophiliac (X^hY) is crossed with a female carrier of both color blindness and hemophilia (X^cX^h) what is the probability that a female child be phenotypically normal?

The answer is 50%

But I don't get quite it because after doing the cross I get X^cX^h and X^hX^h and aren't both of these seen phenotypically? Or is it because the alleles are recessive and requires to have 2 in order to be seen phenotypically? :S

thanks in advance

 

[jefff]

hmm, i was just thinking in reference to x-inactivation...

if all the cells that make clotting factor have the X^c inactivated then she could phenotypically be a hemophiliac

if all the cells that make cone photoreceptors have the X^h inactivated then she could phenotypically be color blind

i guess since there is no way to calculate the probability of x-inactivation in particular cells its best to choose an answer based on the percents obtained when evaluating phenotypic expression of the genotypes