Biology STAAR (State of Texas Assessments of Academic Readiness) Practice Test

Which statement best describes a trait that is sex-linked in males?

1. Males must inherit two copies of the recessive gene

2. Males are less likely to express the trait than females

3. Males are more likely to express the trait due to having one X chromosome

4. Males cannot inherit sex-linked traits

The correct answer is: Males are more likely to express the trait due to having one X chromosome

A trait that is sex-linked in males is best described by the understanding that males possess one X chromosome and one Y chromosome. Therefore, if a trait is carried on the X chromosome, males are more likely to express that trait because they only need to inherit one copy of the recessive allele from their mother. In general, sex-linked traits, especially those that are recessive, will manifest in males when the allele is present on the X chromosome since there is no corresponding allele on the Y chromosome to mask its effect. Thus, the presence of a single X-linked recessive gene is enough for males to exhibit the trait, which is why they are more likely to express sex-linked traits compared to females, who have two X chromosomes and need two copies of the recessive allele to express the same trait.