Can one twin be color blind and the other not?

Yes, it is possible for identical twins to have different phenotypes, including one being color blind and the other not.

While identical twins share the same genetic code, subtle differences in gene expression can lead to variations in physical traits and genetic disorders. Color blindness, also known as color vision deficiency, is a genetic trait primarily determined by genes located on the X chromosome.

Males are more commonly affected by color blindness compared to females because they have only one X chromosome, whereas females have two. If a male inherits a color blindness gene from his mother (who is usually a carrier), he will be color blind. Females need to inherit two copies of the color blindness gene (one from each parent) to express the condition.

In the case of identical twins, if one twin receives the color blindness gene from their mother, while the other twin does not, they will have different color vision. The twin who inherits the gene will have color blindness, while the other twin will have normal color vision.