What describes sex chromosomes?

• A. All chromosomes except the sex chromosome
• B. Pair of chromosomes that determines sex
• C. Two identical chromosomes
• D. Segments of DNA that code for traits

Answer: (B)

Sex chromosomes are the chromosome pair that determines an individual’s sex. In humans, females normally have two X chromosomes (XX) and males have one X and one Y (XY). The presence of the Y chromosome, with its sex-determining genes, directs male development, while the combination of two X chromosomes directs female development. This pair is distinct from autosomes, which are the other 22 chromosome pairs that mostly carry genes unrelated to sex. Saying they are segments of DNA that code for traits is too general, since sex chromosomes are whole chromosomes with many genes, not just small coding segments. Therefore, describing them as the paired chromosomes that determine sex best captures their role.