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

Which trait is most likely to be sex-linked?

1. A trait found on the Y chromosome

2. A trait found exclusively on the X chromosome

3. A trait that is inherited equally from both parents

4. A trait that affects females more than males

The correct answer is: A trait found exclusively on the X chromosome

A trait found exclusively on the X chromosome is the most likely to be sex-linked because sex-linked traits are typically associated with genes located on the sex chromosomes, particularly the X chromosome. In humans, males have one X and one Y chromosome, while females have two X chromosomes. Traits that are located on the X chromosome can manifest differently in males and females due to the presence of only one copy of the X chromosome in males. Since males express whatever allele is present on their single X chromosome, any recessive trait on that chromosome can be expressed without a corresponding allele to mask it, which is not the case for females who have two X chromosomes with the potential for one to compensate for any recessive allele. While traits found on the Y chromosome could potentially also be sex-linked, relatively few traits are located there, and the more common scenario involves the X chromosome. Furthermore, traits that affect females more than males do not necessarily indicate a sex-linked trait as they might arise from other genetic mechanisms or environmental influences. Traits inherited equally from both parents are generally autosomal traits and not linked to the sex chromosomes at all. Therefore, traits found exclusively on the X chromosome are the prime candidates for being classified as sex-linked.