What does sex linkage mean?

Sex linkage refers to when certain alleles affect one gender more than the other. Men tend to be affected by some genetic disorders more than women. This is because some alleles for genetic disorders are carried on the X chromosome. The Y chromosome in males is shorter than the X chromosome so it carries fewer genes. This means that men may only have one copy of a gene for a disorder as it is carried on their one X chromosome. This means that if a gene on their X chromosome codes for a genetic disorder it will be present in the male even if that allele is recessive. However, because women have 2 X chromosomes they will have a second allele for the gene. This means women need two recessive alleles for a recessive X linked disorder to be present, therefore they are affected less often. An example of this is colour blindness. Colour blindness is more frequent in males than females as males only need one copy of the faulty allele.