What term describes a gene located on a sex chromosome?

• A. Sex-linked gene
• B. Autosome
• C. Genome
• D. Karyotype

Answer: (A)

Genes located on sex chromosomes are called sex-linked genes. In humans the sex chromosomes are X and Y, so these genes show inheritance patterns tied to the sex of the individual. Because males have only one X chromosome, any allele on that X is expressed there, while females have two Xs and can mask a recessive allele with a dominant one on the other X. That’s why many sex-linked traits, such as red-green color vision, appear more often in males. This concept differs from autosomal genes, which lie on non-sex chromosomes and don’t show the same sex-biased patterns. A genome is the full set of genetic material, and a karyotype is the visual arrangement of all chromosomes.