In a family where the mother is a carrier for colorblindness and the father has normal vision, which of the following children will have normal vision?

• A. A daughter who is a carrier
• B. A son with normal vision
• C. A daughter who is colorblind
• D. A son who is colorblind

Answer: (B)

Verified step by step guidance

1. Understand that colorblindness is a sex-linked recessive trait, located on the X chromosome. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
2. Identify the genetic makeup of the parents: The mother is a carrier, meaning she has one normal vision allele (X) and one colorblind allele (Xc). The father has normal vision, so his genotype is XY.
3. Determine the possible genotypes for the children: For daughters, they can inherit one X chromosome from each parent, resulting in either XX (normal vision) or XcX (carrier). For sons, they inherit the X chromosome from the mother and the Y chromosome from the father, resulting in either XY (normal vision) or XcY (colorblind).
4. Analyze the options: A daughter who is a carrier (XcX) will have normal vision because the normal allele is dominant. A daughter who is colorblind (XcXc) is not possible with these parents. A son with normal vision (XY) inherits the normal X from the mother. A son who is colorblind (XcY) inherits the colorblind X from the mother.
5. Conclude that the child with normal vision is the son with the genotype XY, as he inherits the normal vision X chromosome from his mother and the Y chromosome from his father.