Humber Admissions Practice Test

What distinguishes X-linked inheritance?

1. It is only applicable to females

2. It is a pattern where a recessive gene is on the X chromosome

3. Both males and females show equal expression

4. It involves only dominant traits

The correct answer is: It is a pattern where a recessive gene is on the X chromosome

X-linked inheritance is characterized by the presence of genes located on the X chromosome, where recessive conditions expressed via those genes can significantly affect phenotypic traits. In many X-linked disorders, males (who have only one X chromosome) are more likely to express traits associated with recessive alleles than females, who have two X chromosomes and may carry a second normal allele that can mask the expression of the recessive trait. In contrast to the other statements, which describe different aspects of inheritance or genetic expression, the correct choice accurately captures the essence of X-linked inheritance. It highlights that the crucial factor is the location of a recessive gene specifically on one of the X chromosomes, which allows for a distinct pattern of inheritance and expression, particularly seen in conditions like hemophilia or color blindness.