Red-green color blindness is x-linked recessive. a woman with normal color vision has a father who is color blind. the woman has a child with a man with normal color vision. which phenotype is not expected?

Question

Biology

Uriah Wolfe

20 July, 09:39

Red-green color blindness is x-linked recessive. a woman with normal color vision has a father who is color blind. the woman has a child with a man with normal color vision. which phenotype is not expected?

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Dean Ware · Answer 1

X-linked recessive disorders require two affected (recessive) alleles Xb to express in the female, but requires (the) only one in the male.

Therefore there are no male carriers. A normal male has the XB allele, and the affected male has the Xb allele.

A female either has 2 XB alleles, in which case she is normal and not a carrier.

If she has XBXb alleles, then she is a carrier, but phenotype is normal.

If she has XbXb alleles, she will exhibit colour-blindness.

Since woman's father has colour-blindness and she has normal vision, she is a carrier, because she has XBXb alleles.

Her husband has normal vision, so he has (one) XB allele.

Here's the Punnett square

Mother XB (father)

XB XBXB (normal vision)

Xb XBXb (carrier)

We see that the XbXb (colour-blindness) case is missing, so the phenotype colour-blind is not expected (unless other medical conditions are present)