Pseudoautosomal region

[5] The monotremes, including the platypus and echidna, have a multiple sex chromosome system, and consequently have 8 pseudoautosomal regions.

So, females can inherit an allele originally present on the Y chromosome of their father.

The function of these pseudoautosomal regions is that they allow the X and Y chromosomes to pair and properly segregate during meiosis in males.

[13] Pairing (synapsis) of the X and Y chromosomes and crossing over (recombination) between their pseudoautosomal regions appear to be necessary for the normal progression of male meiosis.

Structural and/or genetic dissimilarity (due to hybridization or mutation) between the pseudoautosomal regions of the X and Y chromosomes can disrupt pairing and recombination, and consequently cause male infertility.

Detail of a human metaphase spread. A region in the pseudoautosomal region of the short arms of the X chromosome (left) and the Y chromosome (top right) was detected by fluorescent in situ hybridization (green). Chromosomes counterstained in red.
Pseudoautosomal regions are at both termini of the sex chromosomes.
PAR1 contains 16 genes, with PLCXD1 as the furthermost PAR1 gene at the distal telomeric end and XG at the boundary of PAR1 at the centromeric end. PAR2 contains 3 genes, with SPRY3 at the centromeric boundary and IL9R at the distal telomeric end. [ 10 ]