A man and woman have a son who is color blind, a recessive sex-linked trait carried on the X-chromosome, but neither parent is color blind. The woman is now pregnant with their second child. Which of the following statements is true about the second child?

A. A daughter will be color blind because the father is a carrier of the recessive allele.
B. A son will be color blind because the mother is a carrier of the recessive allele.
C. A daughter will not be color blind because the father is not a carrier of the recessive allele.
D. A son will be color blind because the father’s mother must have been a carrier for recessive allele.

If a child has a hereditary gene and neither the Mom or Dad had it, it means it came from higher up in the family tree like the Moms Dad or mom or the dads grandma.

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lucasolvfranco lucasolvfranco · Answer 2 · 2019-09-17T20:36:53+02:00

Answer:

B. A son will be color blind because the mother is a carrier of the recessive allele.

Explanation:

Since color blindness is caused by a disturbance in the sex chromosome X, we can define the expression of the genes of this disorder as follows:

[tex]X^DX^D[/tex] - Normal woman

[tex]X^DX^d[/tex] - Normal woman carrying the recessive gene

[tex]X^dX^d[/tex] - Colorblind woman

[tex]X^DY[/tex] - Normal man

[tex]X^dY[/tex] - Colorblind man

As the father can only donate one X chromosome and it is dominant (D), the son can only be color blind [tex](X^dY)[/tex] if he receives the X chromosome from the mother carrying the recessive allele (d).