Y linkage, also known as sex linkage, or Holandric Inheritance, describes traits that are produced by genes located on the Y chromosome. Y linkage, also known as sex linkage, or Holandric Inheritance, describes traits that are produced by genes located on the Y chromosome. Y linkage can be difficult to detect. This is partly because the Y chromosome is small and contains fewer genes than the autosomal chromosomes or the X chromosome. It is estimated to contain about 200 genes. Earlier, the human Y chromosome was thought to have little importance;. The Y-chromosome is sex-determining in humans and some other species: not all genes that play a role in sex determination are Y-linked. The Y-chromosome, generally does not undergo genetic recombination and only small regions called pseudoautosomal regions exhibit recombination. The majority of the Y-chromosome genes that do not recombine are located in the 'non-recombining region'.