What is sex linkage primarily dependent on?

Sex linkage primarily depends on chromosomal structure. In many organisms, including humans, sex chromosomes (X and Y in mammals) carry different genes, which means that the inheritance patterns of traits linked to these chromosomes can vary significantly between genders. This is because males and females have different combinations of sex chromosomes—males typically have one X and one Y chromosome, while females have two X chromosomes.

This difference in chromosomal structure leads to inheritable traits that are linked to the sex chromosomes, resulting in specific patterns of inheritance that’s associated with one's gender. For example, if a gene for a trait is located on the X chromosome, the expression of that trait may be seen more frequently in males due to their single X chromosome. In contrast, females, having two X chromosomes, may have a different expression pattern due to the possibility of possessing two alleles for that trait.

In light of this understanding, while the gender of the individual plays a role in the manifestation of sex-linked traits, it is fundamentally the chromosomal structure that underlies the concept of sex linkage.