Question

what does it mean for a gene to be sex - linked?
the gene is located on an autosome, but it is only expressed if a barr body or y chromosome is present.
the gene locus is located on a sex chromosome.
the gene is only expressed in gametes. sex - linked genes are not expressed in somatic cells.
the gene is expressed in only one sex, regardless of the chromosome on which it resides.
the gene is located on both an autosome and a sex chromosome, and both of the same alleles must be present for the gene to be expressed.

Explanation:

A sex - linked gene is located on a sex chromosome. Sex chromosomes (such as the X and Y chromosomes in humans) carry genes that are involved in sex - determination and other sex - related traits. When a gene is on a sex chromosome, its inheritance pattern is different from genes on autosomes (non - sex chromosomes). For example, in X - linked inheritance, males (who have one X and one Y chromosome) are more likely to be affected by recessive X - linked disorders because they have only one copy of the X - linked gene.

Answer:

The gene locus is located on a sex chromosome.