A woman gives birth to a set of fraternal twins: a girl and a boy. She also passes on a color-blindness gene. Which of the children is more likely to be color-blind? I think the answer is B.
A. The girl is more likely to be color-blind from birth
B. The boy is more likely to be color-blind from birth
C. The girl will never be color-blind because the gene came from her mother
D. The boy will never be color-blind because the gene came from his mother
Yes, B is correct.
Colorblindness is caused by a recessive gene on the X chromosome. Females usually have two X chromosomes, while males usually only have one X chromosome and one Y chromosome. This means that females need two defective X chromosomes to catch colorblindness, but males only need one.
The correct answer is B. The boy is more likely to be color-blind from birth.
Color blindness is a sex-linked genetic disorder, which means it is carried on the X chromosome. Females have two X chromosomes (XX), and males have one X and one Y chromosome (XY).
If the mother passes on the color-blindness gene, the chances of the children being affected by color blindness depend on their gender:
- If the mother is a carrier (has one normal allele and one color-blindness allele) and the father is not color-blind, there is a 50% chance that a son will inherit the color-blindness allele and be color-blind.
- However, the daughter can only be color-blind if the father is color-blind and the mother is a carrier. In this case, there is a 50% chance that the daughter will inherit the color-blindness allele.
So, while it is possible for the daughter to be color-blind, the boy is more likely to be color-blind if the mother passes on the color-blindness gene. Thus, the correct answer is B.
To determine which child is more likely to be color-blind, we need to understand how color blindness is inherited. Color blindness is usually caused by a recessive gene located on the X chromosome.
In this scenario, the mother passes on the color-blindness gene. Since the mother is carrying the gene, it means she must be a carrier of the gene herself. As women have two X chromosomes, one from each parent, they can be carriers without necessarily being color-blind themselves.
The father, on the other hand, does not pass on an X chromosome to the son because males inherit their X chromosome from their mother, and the Y chromosome from their father.
Based on this information, we can conclude that the boy has a higher likelihood of being color-blind. This is because if the mother is a carrier, there is a 50% chance that she will pass on the color-blindness gene to her son.
Therefore, the correct answer is B. The boy is more likely to be color-blind from birth.