Question

Which of the following statements is true?

The phenotype of a male with color blindness is the same as the phenotype for a female with color blindness.
Most sex-linked disorders are carried on the Y chromosome.
Sex-linked disorders affect males more often than females because males only have one X chromosome.
Sex-linked disorders affect females more often than males because females only have one Y chromosome.

Answer 1

Answer:

3) Sex-linked disorders affect males more often than females because males only have one X chromosome.

Explanation:

1) color blindness is X linked dominant, meaning the gene is on the x chromosome. Women have 2 x chromosomes, so if one of them is affected the other chromosome still has "good" genes. They are only carriers and need 2 affected chromosomes to be express it. Men only have one x and do not have back up x genes. Color blind female - XX, Carrier female -Xx, Color blind male -Xy

Note: Color blind daughters have color blind fathers

2) there are more chances of disorders occurring on the x chromosomes because there are more of them (≈75% of human sex chromosomes are x). A "bad" x chromosome can be passed down several generations without anything happening, while a "bad" y chromosome will always be expressed and die off a lot more easily (natural selection)

3) As stated before, men do not have back up x or y genes that could "take over" if there was a disorder

4) Females do not have a y chromosome