Final answer:
A color-blind woman passes the colorblind gene to her sons because she has the colorblind allele on one of her X chromosomes. Sons inherit their X chromosome from their mother and Y from their father. Daughters will not be colorblind unless they inherit colorblind alleles from both parents. The correct option is 2.
Step-by-step explanation:
Color blindness is a sex-linked recessive trait, typically found on the X chromosome. Since males (XY) only have one X chromosome, if it carries the gene for colorblindness, they will be colorblind.
Women (XX), on the other hand, have two X chromosomes, so they would need two copies of the colorblind gene to exhibit color blindness—one from each parent. This is much rarer since it requires both the mother to be a carrier or affected and the father to be affected or a carrier as well.
This means that the mother carries the colorblind allele on one of her X chromosomes, and since sons inherit their X chromosome from their mother and their Y chromosome from their father, they will be color-blind if they inherit the X chromosome carrying the gene.
Daughters receive one X chromosome from each parent. Since the father is not color-blind, he provides a normal vision allele via his X chromosome, which means the daughter will not be colorblind but may be a carrier if she inherits the colorblind allele from her mother.
- The sex chromosomes of a male are XY, and those of a female are XX.
- Color blindness is X-linked recessive, affecting males more than females.
- A son cannot inherit colorblindness from his father since he inherits the Y chromosome from him, not an X. The correct option is 2.