Question

genetics and heredity exam
color blindness is a recessive trait that is carried on the x chromosome.
a mother is a carrier for color blindness.
the father has normal vision.
which option best explains which offspring has a greater chance of being born color blind?
a son, because he inherits his x chromosome from his mother
a daughter, because she inherits the recessive allele from both parents
sons and daughters have the same chance, because both inherit one x chromosome
neither sons nor daughters can be color blind if the father has normal vision

Explanation:

Color blindness is an X-linked recessive trait. Let the normal allele be $X^C$ and the color blindness allele be $X^c$. The mother (carrier) has genotype $X^CX^c$, and the father (normal vision) has genotype $X^CY$.

• Sons inherit their only X chromosome from the mother and Y from the father. They have a 50% chance of getting $X^c$ (color blind) and 50% chance of $X^C$ (normal).
• Daughters inherit one X from each parent: they will get $X^C$ from the father, so their genotype will be either $X^CX^C$ (normal) or $X^CX^c$ (carrier, not color blind).

Thus, only sons can inherit the trait from this parent pair, with a greater chance than daughters (who cannot be color blind here).

Answer:

A. A son, because he inherits his X chromosome from his mother.