17.9 Sex linkage in man
X and Y chromosomes are different in size. In addition to sex-determining sense they also carry genes for many other traits.
Fig 17.32: the human X chromosome
Many genes are present only on X-chromosome. These have no corresponding alleles on Y-chromosome. These are X-linked genes and their traits are linked traits are also commonly caked sex-linked traits Fig (17.32). A few genes are present only on Y-chromosome, having no counterpart on X-chromosome. These are Y-linked genes and their traits are Y-linked traits. Y-linked traits are found only in males, e.g., maleness. Some genes are present on both X and Y-chromosomes. These are X-and-Y linked genes. As their pattern of inheritance is like autosomal genes, these are also called pseudo autosomal genes.
X being larger has large number of genes, while Y being smaller has small number of genes.
X and Y chromosomes have two distinct regions each due to their linked genes (Fig 17.33).
Fig 17.33: human X and Y chromosomes
- A pairing region with common loci of X-and-Y linked genes due to which they synapse during meiosis.
- A non-pairing of differential region with different gene loci of either X-linked or Y-linked genes.