Color blindness is an X-linked trait in humans.If a color-blind woman marries a man with normal vision, the children will be
A)all color-blind daughters, but normal sons.
B)all color-blind sons, but carrier daughters.
C)all normal sons, but carrier daughters.
D)all color-blind children.
E)all normal children.

Question

Color blindness is an X-linked trait in humans.If a color-blind woman marries a man with normal vision, the children will be
A)all color-blind daughters, but normal sons. 
B)all color-blind sons, but carrier daughters. 
C)all normal sons, but carrier daughters. 
D)all color-blind children. 
E)all normal children.

Quizplus · Accepted Answer

Color blindness is an X-linked recessive trait. Since the woman is color-blind, she must have a genotype of XcXc. The man, having normal vision, must have a genotype of XCY. The possible gametes for the woman are Xc and Xc, while the man produces only X and Y gametes. The offspring will receive one sex chromosome from each parent, resulting in the following gametes:
Xc X
Xc Y
X  X
Y  X
Therefore, the offspring can be:
Color-blind sons (XcY)
Normal sons (XY)
Carrier daughters (XcX or XX)

Since all daughters inherit an X chromosome from the mother, they are all carriers of the color blindness gene. However, the sons only inherit a Y chromosome from the father, so they cannot inherit the color blindness gene from him. Therefore, all of the sons will have normal vision, but all of the daughters will be carriers of the color blindness trait.

Color Blindness Is an X-Linked Trait in Humans