Biological Systems MCAT Practice Exam 2025 – The Comprehensive All-in-One Guide for Exam Success!

Sex-linked traits are indeed characterized by the ability to be carried by one sex without being expressed. This is particularly true for traits that are located on the X chromosome. For example, if a male has a recessive trait on his single X chromosome, he will express that trait because he does not have a second X chromosome to mask it. However, females have two X chromosomes, so they can be carriers of a recessive trait on one X chromosome while still being phenotypically normal if the other X chromosome has a dominant allele. This characteristic of being a carrier without expressing the trait is crucial to understanding the inheritance patterns of sex-linked traits.

The other options do not accurately describe the inheritance of sex-linked traits. Traits are not exclusively inherited from the father; they can be transmitted from either parent depending on the sex chromosomes involved. The claim of exhibiting complete dominance is also misleading, as many sex-linked traits follow a pattern of incomplete dominance or codominance rather than complete dominance. Lastly, sex-linked traits are not always expressed equally in both sexes; instead, they often have different manifestations based on the sex of the individual due to the presence of one or two X chromosomes.