The pseudoautosomal regions, PAR1, PAR2, are homologous sequences of

nucleotide Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules wi ...

s on the X and

Y chromosome The Y chromosome is one of two sex chromosomes (allosomes) in therian mammals, including humans, and many other animals. The other is the X chromosome. Y is normally the sex-determining chromosome in many species, since it is the presence or abse ...

s. The pseudoautosomal regions get their name because any genes within them (so far at least 29 have been found for humans) are inherited just like any

autosomal An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosome, allosomal (sex chromosome) pairs, which may have different structures. The DNA in au ...

genes. PAR1 comprises 2.6 Mbp of the short-arm tips of both X and Y chromosomes in humans and

great apes The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); ''Gorilla'' (the east ...

(X and Y are 155 Mbp and 59 Mbp in total). PAR2 is at the tips of the long arms, spanning 320 kbp.

Location

The locations of the PARs within GRCh38 are: The locations of the PARs within GRCh37 are:

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. The function of these pseudoautosomal regions is that they allow the X and Y

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

s to pair and properly segregate during

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...

in males.

Genes

Pseudoautosomal genes are found in two different locations: PAR1 and PAR2. These are believed to have evolved independently.

PAR1

* pseudoautosomal PAR1 ** AKAP17A **

ASMT N-Acetylserotonin O-methyltransferase, also known as ASMT, is an enzyme which catalyzes the final reaction in melatonin biosynthesis: converting Normelatonin to melatonin. This reaction is embedded in the more general tryptophan metabolism pathw ...

** ASMTL **

CD99 CD99 antigen (Cluster of differentiation 99), also known as MIC2 or single-chain type-1 glycoprotein, is a heavily O-glycosylated transmembrane protein that is encoded by the ''CD99'' gene in humans. The protein has a mass of 32 kD. Unusually for ...

CRLF2 Cytokine receptor-like factor 2 is a protein that in humans is encoded by the ''CRLF2'' gene. It forms a ternary signaling complex with TSLP and interleukin-7 receptor-α, capable of stimulating cell proliferation through activation of STAT3, STAT ...

** CSF2RA ** DHRSX ** GTPBP6 **

IL3RA Interleukin 3 receptor, alpha (low affinity) (IL3RA), also known as CD123 (Cluster of Differentiation 123), is a human gene. Function The protein encoded by this gene is an interleukin 3 specific subunit of a heterodimeric cytokine receptor. T ...

P2RY8 P2Y purinoceptor 8 is a protein that in humans is encoded by the ''P2RY8'' gene. Function The protein encoded by this gene belongs to the family of G-protein coupled receptors, that are preferentially activated by adenosine and uridine nucleot ...

PLCXD1 PI-PLC X domain-containing protein 1, also known as Phosphatidylinositol-specific phospholipase C, X domain containing 1, is an enzyme which in humans is encoded by the ''PLCXD1'' gene. The gene coding for this protein is located in the pseudoaut ...

PPP2R3B Serine/threonine-protein phosphatase 2A regulatory subunit B'' subunit beta is an enzyme that in humans is encoded by the ''PPP2R3B'' gene. Function Protein phosphatase 2 (formerly named type 2A) is one of the four major Ser/Thr phosphatases a ...

SHOX The short-stature homeobox gene (SHOX), also known as short-stature-homeobox-containing gene, is a gene located on both the X and Y chromosomes, which is associated with short stature in humans if mutated or present in only one copy ( haploinsuff ...

SLC25A6 ADP/ATP translocase 3, also known as solute carrier family 25 member 6, is a protein that in humans is encoded by the ''SLC25A6'' gene. Identical copies of this gene reside on the pseudoautosomal regions of the X and Y chromosomes. See also ...

** XG, which straddles the PAR1 region boundary **

ZBED1 Zinc finger BED domain-containing protein 1 is a protein that in humans is encoded by the ''ZBED1'' gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meani ...

mice A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...

, some PAR1 genes have transferred to

autosome An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosome, allosomal (sex chromosome) pairs, which may have different structures. The DNA in au ...

PAR2

* pseudoautosomal PAR2 ** IL9R **

SPRY3 Protein sprouty homolog 3 is a protein that in humans is encoded by the ''SPRY3'' gene. The ''SPRY3'' gene is one of the genes found in the pseudoautosomal regions of the human sex chromosomes A sex chromosome (also referred to as an allosome ...

** VAMP7, also known as SYBL1 ** CXYorf1, also known as FAM39A and now mapped to the pseudogene WASH6P, but of interest due to its proximity to the

telomere A telomere (; ) is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes. Although there are different architectures, telomeres, in a broad sense, are a widespread genetic feature mos ...

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

. Thus, those cells in which X-Y recombination does not occur will fail to complete meiosis. Structural and/or genetic dissimilarity (due to hybridization or

mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mi ...

) 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 gene most commonly associated with and well understood with regards to disorders in humans, but all pseudoautosomal genes escape

X-inactivation X-inactivation (also called Lyonization, after English geneticist Mary Lyon) is a process by which one of the copies of the X chromosome is inactivated in therian female mammals. The inactive X chromosome is silenced by being packaged into ...

and are therefore candidates for having

gene dosage Gene dosage is the number of copies of a particular gene present in a genome. Gene dosage is related to the amount of gene product (proteins or functional RNAs) the cell is able to express. Since, a gene acts as a template, the number of templates ...

effects in sex chromosome

aneuploidy Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more complete sets of chromosomes. A cell with any ...

conditions ( 45,X, 47,XXX,

47,XXY Klinefelter syndrome (KS), also known as 47,XXY, is an aneuploid genetic condition where a male has an additional copy of the X chromosome. The primary features are infertility and small, poorly functioning testicles. Usually, symptoms are subt ...

, 47,XYY, etc.). Deletions have also been associated with Léri-Weill dyschondrosteosis and

Madelung's deformity Madelung's deformity is usually characterized by malformed wrists and wrist bones and is often associated with Léri-Weill dyschondrosteosis. It can be bilateral (in both wrists) or just in the one wrist. It has only been recognized within the pa ...

References

External links

* * {{Chromosomes Molecular genetics Cytogenetics