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 biomolecu ...

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 abs ...

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 allosomal (sex chromosome) pairs, which may have different structures. The DNA in autosom ...

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 ...

(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 ar ...

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 ...

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 pa ...

ASMTL N-acetylserotonin O-methyltransferase-like protein is an enzyme that in humans is encoded by the ''ASMTL'' gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." ...

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 ** CSF2RA **

DHRSX Dehydrogenase/reductase (SDR family) X-linked also known as DHRSX is an enzyme which in humans is encoded by the pseudoautosomal ''DHRSX'' gene. DHRSX is a member of the short-chain dehydrogenase family of oxidoreductase In biochemistry, an oxi ...

GTPBP6 GTP binding protein 6 also known as GTPBP6 is a protein which in humans is encoded by the pseudoautosomal ''GTPBP6'' gene. Clinical significance Overexpression of GTPBP6 as a result of Klinefelter's syndrome Klinefelter syndrome (KS), a ...

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 ** PLCXD1 ** PPP2R3B ** SHOX ** SLC25A6 ** XG, which straddles the PAR1 region boundary ** ZBED1 in

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 allosomal (sex chromosome) pairs, which may have different structures. The DNA in autosomes ...

PAR2

* pseudoautosomal PAR2 **

IL9R Interleukin 9 receptor (IL9R) also known as CD129 (Cluster of Differentiation 129) is a type I cytokine receptor. IL9R also denotes its human gene. The protein encoded by this gene is a cytokine receptor that specifically mediates the biological ...

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 (i.e. those 19 genes that are found on both the ...

VAMP7 Synaptobrevin-like protein 1 (SYBL1), also known as vesicle-associated membrane protein 7 (VAMP7), is a protein that in humans is encoded by the ''VAMP7'', or ''SYBL1'', gene. Function SYBL1 is a transmembrane protein that is a member of the ...

, also known as

SYBL1 Synaptobrevin-like protein 1 (SYBL1), also known as vesicle-associated membrane protein 7 (VAMP7), is a protein that in humans is encoded by the ''VAMP7'', or ''SYBL1'', gene. Function SYBL1 is a transmembrane protein that is a member of the ...

** CXYorf1, also known as FAM39A and now mapped to the

pseudogene Pseudogenes are nonfunctional segments of DNA that resemble functional genes. Most arise as superfluous copies of functional genes, either directly by DNA duplication or indirectly by reverse transcription of an mRNA transcript. Pseudogenes ar ...

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 Hybridization (or hybridisation) may refer to: *Hybridization (biology), the process of combining different varieties of organisms to create a hybrid *Orbital hybridization, in chemistry, the mixing of atomic orbitals into new hybrid orbitals *Nu ...

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, m ...

) between the pseudoautosomal regions of the X and Y chromosomes can disrupt pairing and recombination, and consequently cause male infertility. The

SHOX gene 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 ( haploinsu ...

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 and are therefore candidates for having gene dosage 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 an ...

conditions ( 45,X,

47,XXX Trisomy X, also known as triple X syndrome and characterized by the karyotype 47,XXX, is a chromosome disorder in which a female has an extra copy of the X chromosome. It is relatively common and occurs in 1 in 1,000 women but it is rarely diag ...

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 pas ...

References

External links

* * {{Chromosomes Molecular genetics Cytogenetics