Humber Admissions Practice Test

Which inheritance pattern increases the likelihood of males being affected by a recessive trait?

1. Complete dominance

2. X-linked inheritance

3. Incomplete dominance

4. Polygenic inheritance

The correct answer is: X-linked inheritance

The inheritance pattern that increases the likelihood of males being affected by a recessive trait is X-linked inheritance. This pattern is significant because genes located on the X chromosome have a different impact on males and females due to their chromosomal compositions. Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX). In the case of X-linked recessive traits, a single recessive allele on the X chromosome can express the trait in males since there is no corresponding allele on the Y chromosome to mask it. Therefore, if a male inherits an X chromosome with a recessive trait, he will exhibit the disorder. In contrast, for females to express an X-linked recessive trait, they must inherit the recessive allele on both of their X chromosomes. This means that while females can be carriers of such traits, they are less likely to be affected than males. This difference in inheritance patterns due to the sex chromosomes explains why X-linked inheritance results in a higher prevalence of recessive traits in males compared to females.