Question

Non-Mendelian inheritance patterns can be sorted into three categories: incomplete dominance, codominance, and sex-linked traits. Which is an example of a sex-linked trait?
A) Down's syndrome
B) Color blindness
C) Human blood type
D) Tail length in dogs

Answer 1

Answer: B (Color blindness)

Explanation:

Typical red-green color blindness in human patients is caused by mutations on genes located in the X chromosome. These mutations act in a recessive manner. Since females have two X chromosomes, the presence of a mutation in a single one of them does not normally result in color blindness. Males, in contrast, have a single X chromosome and therefore the presence of a mutation is likely to cause the disease.

About the other options: Down‘s syndrome is a numerical chromosomal anomaly, not related to sex. Human blood type is a codominant trait. Finally, tail length in dogs is a polygenic trait not amenable to classic Mendelian analysis.