Genes that are located on the X or Y chromosome are said to be ______ and often are expressed in one sex more than the other.

Genes that are located on the X or Y chromosome are said to be sex-linked and often are expressed in one sex more than the other. This is because these genes can have different modes of inheritance and expression between males and females due to the differences in the sex chromosomes. For example, since males have one X and one Y chromosome (XY), any allele on the X chromosome is expressed in males regardless of whether it is dominant or recessive. In contrast, females have two X chromosomes (XX), so they require two copies of a recessive allele on the X chromosome for that trait to be expressed. This can lead to differences in the prevalence of certain genetic disorders and traits between the sexes.