Pseudoautosomal region

Pseudoautosomal region are specific regions of both sex chromosomes (that is the, X chromosome and the Y chromosome). Genes are located in these regions, which have their homologous copies (in the same order) also on the second type of heterochromosome. In the case of the X-chromosome, these genes are not subject to Ionisation. For genes located in these regions, the autosomal type of inheritance applies.

There are two sections – PAR 1 (larger section, approx. 2.7Mb = millions of bases, 24 genes) at the end of the short arms and PAR 2 smaller section, approx. 330kb = thousands of bases, 5 genes) at the end of the long arms. Thanks to these regions (primarily PAR1), the X and Y chromosomes can form a "homologous" pair during meiosis; crossing-over can occur between genes in these regions.

Although it might seem logical that PAR1 and PAR2 represent a remnant of the original autosome from which the X chromosome and the Y chromosome arose, it appears that the PAR1 region was added to both chromosomes 29-44 million years ago by a complex process of multiple translocations. PAR2 of the chromosome Y is derived from the chromosome X, its transmission occurred within the evolution of primates about 4-10 million years ago.

An example of a gene in the PAR1 region can be the SHOX gene (Short Stature Homeobox; Xp22.32; (OMIM ) and its homologue the SHOXY gene ( Yp11.2; (OMIM ).

related articles

 * X chromosome
 * X-chromosome inactivation
 * Sex chromosome
 * Turner syndrome
 * X-linked inheritance