Everything about The Pseudoautosomal Region totally explained
The
pseudoautosomal regions,
PAR1 and
PAR3 are
homologous sequences of
nucleotides on the
X and
Y chromosomes
The pseudoautosomal regions get their name because any genes located within them (so far at least 29 have been found) are inherited just like any
autosomal genes.
Inheritance and function
Normal male mammals have two copies of these genes: one in the pseudoautosomal region of their Y chromosome, the other in the corresponding portion of their X chromosome. Normal females also possess two copies of pseudoautosomal genes, as each of their two X chromosomes contains a pseudoautosomal region. Crossing over between the X and Y chromosomes is normally restricted to the pseudoautosomal regions; thus, pseudoautosomal genes exhibit an autosomal, rather than sex-linked, pattern of inheritance. So, females can inherit an allele originally present on the Y chromosome of their father and males can inherit an allele originally present on the X 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.
Pathology
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. Thus, those cells in which X-Y recombination doesn't occur will fail to complete 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.
The
SHOX gene in the PAR1 region is the only gene that has so far been shown to be associated with disorders in humans, but all pseudoautosomal genes escape
X-inactivation and are therefore candidates for having
gene dosage effects in sex chromosome
aneuploidy conditions (
45,X,
47,XXX,
47,XXY,
47,XYY, etc.).
Further Information
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