Y chromosome - AbsoluteAstronomy.com

The Y chromosome is one of the two sex-determining

Sex-determination system

A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most sexual organisms have two sexes. In many cases, sex determination is genetic: males and females have different alleles or even different genes that specify their sexual...

chromosome

Chromosome

A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...

s in most mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s, including human

Human

Humans are the only living species in the Homo genus...

s. In mammals, it contains the gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

SRY

SRY is a sex-determining gene on the Y chromosome in the therians .This intronless gene encodes a transcription factor that is a member of the SOX gene family of DNA-binding proteins...

, which triggers testis

Testicle

The testicle is the male gonad in animals. Like the ovaries to which they are homologous, testes are components of both the reproductive system and the endocrine system...

development if present. The human Y chromosome is composed of about 60 million base pairs. DNA in the Y chromosome is passed from father to son, and Y-DNA analysis may thus be used in genealogy research.

Overview

Most mammals have one pair of sex chromosomes in each cell. Males have one Y chromosome and one X chromosome

X chromosome

The X chromosome is one of the two sex-determining chromosomes in many animal species, including mammals and is common in both males and females. It is a part of the XY sex-determination system and X0 sex-determination system...

, while females have two X chromosomes. In mammals, the Y chromosome contains a gene, SRY

SRY

SRY is a sex-determining gene on the Y chromosome in the therians .This intronless gene encodes a transcription factor that is a member of the SOX gene family of DNA-binding proteins...

, which triggers embryonic development as a male. The Y chromosomes of humans and other mammals also contain other genes needed for normal sperm production.

There are exceptions, however. For example, the platypus

Platypus

The platypus is a semi-aquatic mammal endemic to eastern Australia, including Tasmania. Together with the four species of echidna, it is one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth to live young...

relies on an XY sex-determination system

XY sex-determination system

The XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects and some plants . In this system, females have two of the same kind of sex chromosome , and are called the homogametic sex. Males have two distinct sex chromosomes , and are called...

based on five pairs of chromosomes. Platypus sex chromosomes in fact appear to bear a much stronger homology

Homology (biology)

Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...

(similarity) with the avian Z chromosome

ZW sex-determination system

The ZW sex-determination system is a system that determines the sex of offspring in birds, some fish and crustaceans such as the giant river prawn, some insects , and some reptiles, including Komodo dragons...

, and the SRY gene so central to sex-determination in most other mammals is apparently not involved in platypus sex-determination. Among humans, some men have two Xs and a Y ("XXY", see Klinefelter's syndrome

Klinefelter's syndrome

Klinefelter syndrome, 46/47, XXY, or XXY syndrome is a condition in which human males have an extra X chromosome. While females have an XX chromosomal makeup, and males an XY, affected individuals have at least two X chromosomes and at least one Y chromosome...

), or one X and two Ys (see XYY syndrome

XYY syndrome

XYY syndrome is an aneuploidy of the sex chromosomes in which a human male receives an extra Y-chromosome, giving a total of 47 chromosomes instead of the more usual 46. This produces a 47,XYY karyotype...

), and some women have three Xs

Triple X syndrome

Triple X syndrome is a form of chromosomal variation characterized by the presence of an extra X chromosome in each cell of a human female. The condition always produces females, with an XX pair of chromosomes, as well as an additional chromosome, resulting in the formation of XXX. A mosaic form...

or a single X instead of a double X ("X0", see Turner syndrome

Turner syndrome

Turner syndrome or Ullrich-Turner syndrome encompasses several conditions in human females, of which monosomy X is most common. It is a chromosomal abnormality in which all or part of one of the sex chromosomes is absent...

). There are other exceptions in which SRY

SRY

SRY is a sex-determining gene on the Y chromosome in the therians .This intronless gene encodes a transcription factor that is a member of the SOX gene family of DNA-binding proteins...

is damaged (leading to an XY female

Swyer syndrome

Swyer syndrome, or XY gonadal dysgenesis, is a type of hypogonadism in a person whose karyotype is 46,XY. The person is externally female with streak gonads, and left untreated, will not experience puberty...

), or copied to the X (leading to an XX male). For related phenomena see Androgen insensitivity syndrome

Androgen insensitivity syndrome

Androgen insensitivity syndrome is a condition that results in the partial or complete inability of the cell to respond to androgens. The unresponsiveness of the cell to the presence of androgenic hormones can impair or prevent the masculinization of male genitalia in the developing fetus, as...

and Intersex

Intersex

Intersex, in humans and other animals, is the presence of intermediate or atypical combinations of physical features that usually distinguish female from male...

Before Y chromosome

Many ectotherm

Ectotherm

An ectotherm, from the Greek εκτός "outside" and θερμός "hot", refers to organisms that control body temperature through external means. As a result, organisms are dependent on environmental heat sources and have relatively low metabolic rates. For example, many reptiles regulate their body...

ic vertebrates have no sex chromosomes. If they have different sexes, sex is determined environmentally rather than genetically. For some of them, especially reptile

Reptile

Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s, sex depends on the incubation temperature; others are hermaphroditic (meaning they contain both male and female gametes in the same individual).

Origin

The X and Y chromosomes are thought to have evolved from a pair of identical chromosomes, termed autosomes, when an ancestral mammal developed an allelic variation, a so-called 'sex locus' – simply possessing this allele

Allele

An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...

caused the organism to be male. The chromosome with this allele became the Y chromosome, while the other member of the pair became the X chromosome. Over time, genes which were beneficial for males and harmful to (or had no effect on) females either developed on the Y chromosome, or were acquired through the process of translocation

Chromosomal translocation

In genetics, a chromosome translocation is a chromosome abnormality caused by rearrangement of parts between nonhomologous chromosomes. A gene fusion may be created when the translocation joins two otherwise separated genes, the occurrence of which is common in cancer. It is detected on...

.

Until recently, the X and Y chromosomes were thought to have diverged around 300 million years ago. However, recent research, particularly that stemming from the sequencing of the platypus genome, has suggested that the XY sex-determination system wouldn't have been present more than 166 million years ago, at the split of the monotremes from other mammals. This reestimation of the age of the therian XY system is based on the finding that sequences that are on the X chromosomes of marsupials and eutherian mammals are present on the autosomes of platypus and birds. The older estimate was based on erroneous reports that the platypus X chromosomes contained these sequences.

Recombination inhibition

Recombination

Genetic recombination

Genetic recombination is a process by which a molecule of nucleic acid is broken and then joined to a different one. Recombination can occur between similar molecules of DNA, as in homologous recombination, or dissimilar molecules, as in non-homologous end joining. Recombination is a common method...

between the X and Y chromosomes proved harmful—it resulted in males without necessary genes formerly found on the Y chromosome, and females with unnecessary or even harmful genes previously only found on the Y chromosome. As a result, genes beneficial to males accumulated near the sex-determining genes, and recombination in this region was suppressed in order to preserve this male specific region. Over time, the Y chromosome changed in such a way as to inhibit the areas around the sex determining genes from recombining at all with the X chromosome. As a result of this process 95% of the human Y chromosome is unable to recombine.

Shrinking

The human Y chromosome has lost 1,393 of its 1,438 original genes over the course of its existence. With a rate of genetic loss of 4.6 genes per million years, the Y chromosome may potentially lose complete function within the next 10 million years. Comparative genomic analysis, however, reveals that many mammalian species are experiencing a similar loss of function in their heterozygous sex chromosome. Degeneration may simply be the fate of all nonrecombining sex chromosomes due to three common evolutionary forces: high mutation rate

Mutation rate

In genetics, the mutation rate is the chance of a mutation occurring in an organism or gene in each generation...

, inefficient selection

Selection

In the context of evolution, certain traits or alleles of genes segregating within a population may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively—meaning they contribute more offspring to the...

and genetic drift

Genetic drift

Genetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...

. On the other hand, recent comparisons of the human and chimpanzee

Chimpanzee

Chimpanzee, sometimes colloquially chimp, is the common name for the two extant species of ape in the genus Pan. The Congo River forms the boundary between the native habitat of the two species:...

Y chromosomes show that the human Y chromosome has not lost any genes since the divergence of humans and chimpanzees between 6–7 million years ago, providing direct evidence that the linear extrapolation model is flawed.

High mutation rate

The human Y chromosome is particularly exposed to high mutation rates due to the environment in which it is housed. The Y chromosome is passed exclusively through sperm

Sperm

The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...

, which undergo multiple cell division

Cell division

Cell division is the process by which a parent cell divides into two or more daughter cells . Cell division is usually a small segment of a larger cell cycle. This type of cell division in eukaryotes is known as mitosis, and leaves the daughter cell capable of dividing again. The corresponding sort...

s during gametogenesis

Gametogenesis

Gametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic division of diploid gametocytes into various gametes,...

. Each cellular division provides further opportunity to accumulate base pair mutations. Additionally, sperm are stored in the highly oxidative environment of the testis, which encourages further mutation. These two conditions combined put the Y chromosome at a risk of mutation 4.8 times greater than the rest of the genome.

Inefficient selection

Without the ability to recombine during meiosis

Meiosis

Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....

, the Y chromosome is unable to expose individual allele

Allele

s to natural selection. Deleterious alleles are allowed to "hitchhike" with beneficial neighbors, thus propagating maladapted alleles in to the next generation. Conversely, advantageous alleles may be selected against if they are surrounded by harmful alleles (background selection). Due to this inability to sort through its gene content, the Y chromosome is particularly prone to the accumulation of "junk" DNA. Massive accumulations of retrotransposable elements are scattered throughout the Y. The random insertion of DNA segments often disrupts encoded gene sequences and renders them nonfunctional. However, the Y chromosome has no way of weeding out these "jumping genes". Without the ability to isolate alleles, selection cannot effectively act upon them.

A clear, quantitative indication of this inefficiency is the entropy rate

Entropy rate

In the mathematical theory of probability, the entropy rate or source information rate of a stochastic process is, informally, the time density of the average information in a stochastic process...

of the Y chromosome. Whereas all other chromosomes in the human genome

Human genome

The human genome is the genome of Homo sapiens, which is stored on 23 chromosome pairs plus the small mitochondrial DNA. 22 of the 23 chromosomes are autosomal chromosome pairs, while the remaining pair is sex-determining...

have entropy rates of 1.5–1.9 bits per nucleotide (compared to the theoretical maximum of exactly 2 for no redundancy), the Y chromosome's entropy rate is only 0.84. This means the Y chromosome has a much lower information content relative to its overall length; it is more redundant.

Genetic drift

Even if a well adapted Y chromosome manages to maintain genetic activity by avoiding mutation accumulation, there is no guarantee it will be passed down to the next generation. The population size of the Y chromosome is inherently limited to 1/4 that of autosomes: diploid organisms contain two copies of autosomal chromosomes while only half the population contains 1 Y chromosome. Thus, genetic drift is an exceptionally strong force acting upon the Y chromosome. Through sheer random assortment, an adult male may never pass on his Y chromosome if he only has female offspring. Thus, although a male may have a well adapted Y chromosome free of excessive mutation, it may never make it in to the next gene pool. The repeat random loss of well-adapted Y chromosomes, coupled with the tendency of the Y chromosome to evolve to have more deleterious mutations rather than less for reasons described above, contributes to the species-wide degeneration of Y chromosomes through Muller's ratchet

Muller's ratchet

In evolutionary genetics, Muller's ratchet is the process by which the genomes of an asexual population accumulate deleterious mutations in an irreversible manner....

Gene conversion

In 2003, researchers from MIT discovered a process which may slow down the process of degradation.
They found that human Y chromosome is able to "recombine" with itself, using palindrome

Palindrome

A palindrome is a word, phrase, number, or other sequence of units that can be read the same way in either direction, with general allowances for adjustments to punctuation and word dividers....

base pair

Base pair

In molecular biology and genetics, the linking between two nitrogenous bases on opposite complementary DNA or certain types of RNA strands that are connected via hydrogen bonds is called a base pair...

sequences. Such a "recombination" is called gene conversion

Gene conversion

Gene conversion is an event in DNA genetic recombination, which occurs at high frequencies during meiotic division but which also occurs in somatic cells. It is a process by which DNA sequence information is transferred from one DNA helix to another DNA helix, whose sequence is altered.It is one...

.

In the case of the Y chromosomes, the palindrome

Palindrome

A palindrome is a word, phrase, number, or other sequence of units that can be read the same way in either direction, with general allowances for adjustments to punctuation and word dividers....

s are not noncoding DNA

Noncoding DNA

In genetics, noncoding DNA describes components of an organism's DNA sequences that do not encode for protein sequences. In many eukaryotes, a large percentage of an organism's total genome size is noncoding DNA, although the amount of noncoding DNA, and the proportion of coding versus noncoding...

; these strings of bases contain functioning genes important for male fertility. Most of the sequence pairs are greater than 99.97% identical. The extensive use of gene conversion may play a role in the ability of the Y chromosome to edit out genetic mistakes and maintain the integrity of the relatively few genes it carries. In other words, since the Y chromosome is single, it has duplicates of its genes on itself instead of having a second, homologous, chromosome. When errors occur, it can use other parts of itself as a template to correct them.

Findings were confirmed by comparing similar regions of the Y chromosome in humans to the Y chromosomes of chimpanzee

Chimpanzee

Chimpanzee, sometimes colloquially chimp, is the common name for the two extant species of ape in the genus Pan. The Congo River forms the boundary between the native habitat of the two species:...

s, bonobo

Bonobo

The bonobo , Pan paniscus, previously called the pygmy chimpanzee and less often, the dwarf or gracile chimpanzee, is a great ape and one of the two species making up the genus Pan. The other species in genus Pan is Pan troglodytes, or the common chimpanzee...

s and gorilla

Gorilla

Gorillas are the largest extant species of primates. They are ground-dwelling, predominantly herbivorous apes that inhabit the forests of central Africa. Gorillas are divided into two species and either four or five subspecies...

s. The comparison demonstrated that the same phenomenon of gene conversion appeared to be at work more than 5 million years ago, when humans and the non-human primates diverged from each other.

Future evolution

In the terminal stages of the degeneration of the Y chromosome, other chromosomes increasingly take over genes and functions formerly associated with it. Finally, the Y chromosome disappears entirely, and a new sex-determining system arises. Several species of rodent

Rodent

Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....

in the sister families Muridae

Muridae

Muridae is the largest family of mammals. It contains over 600 species found naturally throughout Eurasia, Africa, and Australia. They have been introduced worldwide. The group includes true mice and rats, gerbils, and relatives....

and Cricetidae

Cricetidae

The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, and New World rats and mice...

have reached these stages, in the following ways:

The Transcaucasian mole vole
Transcaucasian Mole Vole
The Transcaucasian Mole Vole is a species of rodent in the family Cricetidae.It is found in Armenia, Azerbaijan, Georgia, Iran, and Turkey.-References:...

, Ellobius lutescens, the Zaisan mole vole
Zaisan Mole Vole
The Zaisan Mole Vole is a species of rodent in the family Cricetidae.It is found in China, Kazakhstan, Mongolia, Turkmenistan, and Uzbekistan.-References:...

, Ellobius tancrei, and the Japanese spinous country rats Tokudaia osimensis and Tokudaia muenninki, have lost the Y chromosome and SRY
SRY
SRY is a sex-determining gene on the Y chromosome in the therians .This intronless gene encodes a transcription factor that is a member of the SOX gene family of DNA-binding proteins...

entirely. Tokudaia
Tokudaia
Tokudaia is a genus of murine rodent native to Japan. Known as Ryūkyū spiny rats or spinous country-rats, population groups exist on several non-contiguous islands...

spp. have relocated some other genes ancestrally present on the Y chromosome to the X chromosome. Both genders of Tokudaia spp. and Ellobius lutescens have an XO genotype, whereas all Ellobius tancrei possess an XX genotype. The new sex-determining system for these rodents remains unclear.
The wood lemming
Wood Lemming
The Wood Lemming is a species of rodent in the family Cricetidae. It belongs into the Arvicolinae subfamily of rodents therefore is a relative of the voles, lemmings, and muskrats....

Myopus schisticolor, the arctic lemming
Arctic Lemming
The Arctic Lemming is a species of rodent in the family Cricetidae.It is found only in The Arctic Biomes in Russia and Canada.-References:...

, Dicrostonyx torquatus, and multiple species in the grass mouse genus Akodon
Akodon
Akodon is a genus consisting of South American grass mice. They mostly occur south of the Amazon Basin and along the Andes north to Venezuela, but are absent from much of the basin itself, the far south of the continent, and the lowlands west of the Andes. Akodon is one of the most species-rich...

have evolved fertile females who possess the genotype generally coding for males, XY, in addition to the ancestral XX female, through a variety of modifications to the X and Y chromosomes.
In the creeping vole
Creeping Vole
The Creeping Vole is a species of rodent in the family Cricetidae.It is found in British Columbia in Canada and in California, Oregon and Washington in the United States.-References:...

, Microtus oregoni, the females, with just one X chromosome each, produce X gametes only, and the males, XY, produce Y gametes, or gametes devoid of any sex chromosome, through nondisjunction
Nondisjunction
Nondisjunction is the failure of chromosome pairs to separate properly during meiosis stage 1 or stage 2. This could arise from a failure of homologous chromosomes to separate in meiosis I, or the failure of sister chromatids to separate during meiosis II or mitosis. The result of this error is a...

.

Outside of the rodent family, the black muntjac, Muntiacus crinifrons, evolved new X and Y chromosomes through fusions of the ancestral sex chromosomes and autosomes. Primate Y chromosomes, including in humans, have degenerated so much that primates will also evolve new sex determination systems relatively soon, in about 14 million years in humans.

Human Y chromosome

In humans, the Y chromosome spans about 58 million base pair

Base pair

s (the building blocks of DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

) and represents approximately 2% of the total DNA in a male cell

Cell (biology)

The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

. The human Y chromosome contains 86 genes, which code for only 23 distinct proteins. Traits that are inherited via the Y chromosome are called holandric traits.

The human Y chromosome is unable to recombine with the X chromosome, except for small pieces of pseudoautosomal region

Pseudoautosomal region

The pseudoautosomal regions, PAR1 and PAR2 are homologous sequences of nucleotides on the X and Y chromosomes.The pseudoautosomal regions get their name because any genes located within them are inherited just like any autosomal genes...

s at the telomere

Telomere

A telomere is a region of repetitive DNA sequences at the end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes. Its name is derived from the Greek nouns telos "end" and merοs "part"...

s (which comprise about 5% of the chromosome's length). These regions are relics of ancient homology

Homology (biology)

between the X and Y chromosomes. The bulk of the Y chromosome which does not recombine is called the "NRY" or non-recombining region of the Y chromosome. It is the SNP

Single nucleotide polymorphism

A single-nucleotide polymorphism is a DNA sequence variation occurring when a single nucleotide — A, T, C or G — in the genome differs between members of a biological species or paired chromosomes in an individual...

s in this region which are used for tracing direct paternal ancestral lines.

Genes

Not including pseudoautosomal genes, genes include:

NRY, with corresponding gene on X chromosome
X chromosome
The X chromosome is one of the two sex-determining chromosomes in many animal species, including mammals and is common in both males and females. It is a part of the XY sex-determination system and X0 sex-determination system...
- AMELY
  AMELY
  Amelogenin, Y isoform is a protein that in humans is encoded by the AMELY gene.AMELY is a gene which encodes a form of amelogenin found on the Y chromosome. Amelogenin is a member of a family of extracellular matrix proteins. They are involved in biomineralization during tooth enamel development...
  
  /AMELX
  AMELX
  Amelogenin, X isoform is a protein that in humans is encoded by the AMELX gene.Amelogenin, X isoform is a form of amelogenin found on the X chromosome. Amelogenin X is a member of the amelogenin family of extracellular matrix proteins...
  
  (amelogenin
  Amelogenin
  Amelogenin is a protein found in developing tooth enamel, and it belongs to a family of extracellular matrix proteins. Developing enamel contains about 30% protein, and 90% of this is amelogenins...
  
  )
- RPS4Y1
  RPS4Y1
  40S ribosomal protein S4, Y isoform 1 is a protein that in humans is encoded by the RPS4Y1 gene.Cytoplasmic ribosomes, organelles that catalyze protein synthesis, consist of a small 40S subunit and a large 60S subunit. Together these subunits are composed of 4 RNA species and approximately 80...
  
  /RPS4Y2
  RPS4Y2
  Ribosomal protein S4, Y-linked 2 also known as RPS4Y2 is a protein which in humans is encoded by the RPS4Y2 gene which resides on the Y chromosome.-Function:...
  
  /RPS4X
  RPS4X
  40S ribosomal protein S4, X isoform is a protein that in humans is encoded by the RPS4X gene.-Further reading:...
  
  (Ribosomal protein S4)

NRY, other
- AZF1
  AZF1
  Azoospermia factor refers to one of several proteins or their genes, which are coded from the AZF region on the human male Y chromosome. Deletions in this region are associated with inability to produce sperm. Subregions within the AZF region are AZFa , AZFb and AZFc...
  
  (azoospermia
  Azoospermia
  Azoospermia is the medical condition of a male not having any measurable level of sperm in his semen. It is associated with very low levels of fertility or even sterility, but many forms are amenable to medical treatment...
  
  factor 1)
- BPY2
  BPY2
  Testis-specific basic protein Y 2 also known as basic charge, Y-linked 2 is a protein that in humans is encoded by the BPY2 gene which resides on the Y chromosome.- Function :...
  
  (basic protein on the Y chromosome)
- DAZ1
  DAZ1
  Deleted in azoospermia 1, also known as DAZ1, is a protein which in humans is encoded by the DAZ1 gene.- Function :This gene is a member of the DAZ gene family and is a candidate for the human Y-chromosomal azoospermia factor . Its expression is restricted to pre-meiotic germ cells, particularly in...
  
  (deleted in azoospermia)
- DAZ2
  DAZ2
  Deleted in azoospermia protein 2 is a protein that in humans is encoded by the DAZ2 gene.-Further reading:...
- PRKY
  PRKY
  Serine/threonine-protein kinase PRKY is an enzyme that in humans is encoded by the PRKY gene.-Further reading:...
  
  (protein kinase, Y-linked)
- RBMY1A1
  RBMY1A1
  RNA-binding motif protein, Y chromosome, family 1 member A1/C is a protein that in humans is encoded by the RBMY1A1 gene.-Further reading:...
- SRY
  SRY
  SRY is a sex-determining gene on the Y chromosome in the therians .This intronless gene encodes a transcription factor that is a member of the SOX gene family of DNA-binding proteins...
  
  (sex-determining region)
- TSPY
  TSPY1
  Testis-specific Y-encoded protein 1 is a protein that in humans is encoded by the TSPY1 gene.-Further reading:...
  
  (testis-specific protein)
- USP9Y
  USP9Y
  Ubiquitin specific peptidase 9, Y-linked , also known as USP9Y, is an enzyme which in humans is encoded by the USP9Y gene. It is required for sperm production...
- UTY
  UTY (gene)
  Histone demethylase UTY is an enzyme that in humans is encoded by the UTY gene.-Interactions:UTY has been shown to interact with TLE1.-Further reading:...
  
  (ubiquitously transcribed TPR gene on Y chromosome)
- ZFY
  ZFY
  Zinc finger Y-chromosomal protein is a protein that in humans is encoded by the ZFY gene.-Further reading:...
  
  (zinc finger protein
  Zinc finger protein
  A zinc finger protein is a DNA-binding protein domain consisting of zinc fingers ranging from two in the Drosophila regulator ADR1, the more common three in mammalian Sp1 up to nine in TFIIIA...
  
  )

Y chromosome-linked diseases

Y chromosome-linked diseases can be of more common types, or very rare ones. Yet, the rare ones still have importance in understanding the function of the Y chromosome in the normal case.

More common

No vital genes reside only on the Y chromosome, since roughly half of humans (females) do not have Y chromosomes. The only well-defined human disease linked to a defect on the Y chromosome is defective testicular development (due to deletion or deleterious mutation of SRY). However, having two X chromosomes and one Y chromosome has similar effects. On the other hand, having Y chromosome polysomy has other effects than masculinization.

Defective Y chromosome

This results in the person presenting a female phenotype

Phenotype

A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...

even though that person possesses an XY karyotype

Karyotype

A karyotype is the number and appearance of chromosomes in the nucleus of an eukaryotic cell. The term is also used for the complete set of chromosomes in a species, or an individual organism.p28...

(i.e., is born with female-like genitalia). The lack of the second X results in infertility. In other words, viewed from the opposite direction, the person goes through defeminization

Defeminization

Defeminization is a term in developmental biology, especially zoology, referring to an aspect of the process of sexual differentiation by which a potential female-specific structure, function, or behavior is prevented from developing by one of the processes of male development...

but fails to complete masculinization.

The cause can be seen as an incomplete Y chromosome: the usual karyotype in these cases is 44X, plus a fragment of Y. This usually results in defective testicular development, such that the infant may or may not have fully formed male genitalia internally or externally. The full range of ambiguity of structure may occur, especially if mosaicism is present. When the Y fragment is minimal and nonfunctional, the child is usually a girl with the features of Turner syndrome

Turner syndrome

or mixed gonadal dysgenesis

Mixed gonadal dysgenesis

Mixed gonadal dysgenesis is a condition of unusual and asymmetrical gonadal development leading to an unassigned sex differentiation. A number of differences have been reported in the karyotype, most commonly a mosaicism 45,X/ 46, XY...

XXY

Klinefelter's syndrome

(47, XXY) is not an aneuploidy

Aneuploidy

Aneuploidy is an abnormal number of chromosomes, and is a type of chromosome abnormality. An extra or missing chromosome is a common cause of genetic disorders . Some cancer cells also have abnormal numbers of chromosomes. Aneuploidy occurs during cell division when the chromosomes do not separate...

of the Y chromosome, but a condition of having an extra X chromosome, which usually results in defective postnatal testicular function. The mechanism is not fully understood; the extra X does not seem to be due to direct interference with expression of Y genes.

XYY

47,XYY syndrome is caused by the presence of a single extra copy of the Y chromosome in each of a male's cells. 47, XYY males have one X chromosome and two Y chromosomes, for a total of 47 chromosomes per cell. Researchers have found that an extra copy of the Y chromosome is associated with increased stature and an increased incidence of learning problems in some boys and men, but the effects are variable, often minimal, and the vast majority do not know their karyotype. When chromosome surveys were done in the mid-1960s in British secure hospitals for the developmentally disabled, a higher than expected number of patients were found to have an extra Y chromosome. The patients were mischaracterized as aggressive and criminal, so that for a while an extra Y chromosome was believed to predispose a boy to antisocial behavior (and was dubbed the "criminal karyotype"). Subsequently, in 1968 in Scotland the only ever comprehensive nationwide chromosome survey of prisons found no overrepresentation of 47,XYY men, and later studies found 47,XYY boys and men had the same rate of criminal convictions as 46,XY boys and men of equal intelligence. Thus, the "criminal karyotype" concept is inaccurate and obsolete.

Rare

The following Y Chromosome-linked diseases are rare, but notable because of their elucidating of the nature of the Y chromosome.

More than two Y chromosomes

Greater degrees of Y chromosome polysomy (having more than one extra copy of the Y chromosome in every cell, e.g., XYYYY) are rare. The extra genetic material in these cases can lead to skeletal abnormalities, decreased IQ, and delayed development, but the severity features of these conditions are variable.

XX male syndrome

XX male syndrome is a rare sex chromosomal disorder. Usually it is caused by unequal crossing over between X and Y chromosomes during meiosis in the father, which results in the X chromosome containing the normally-male SRY gene...

occurs when there has been a recombination

Genetic recombination

in the formation of the male gametes, causing the SRY

SRY

SRY is a sex-determining gene on the Y chromosome in the therians .This intronless gene encodes a transcription factor that is a member of the SOX gene family of DNA-binding proteins...

-portion of the Y chromosome to move to the X chromosome. When such an X chromosome contributes to the child, the development will lead to a male, because of the SRY gene.

Genetic genealogy

In human genetic genealogy

Genetic genealogy

Genetic genealogy is the application of genetics to traditional genealogy. Genetic genealogy involves the use of genealogical DNA testing to determine the level of genetic relationship between individuals.-History:...

(the application of genetics

Genetics

Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

to traditional genealogy

Genealogy

Genealogy is the study of families and the tracing of their lineages and history. Genealogists use oral traditions, historical records, genetic analysis, and other records to obtain information about a family and to demonstrate kinship and pedigrees of its members...

) use of the information contained in the Y chromosome is of particular interest since, unlike other genes, the Y chromosome is passed exclusively from father to son. Mitochondrial DNA

Mitochondrial DNA

Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...

, maternally inherited, is used in an analogous way to trace the maternal line.

Non-mammal Y chromosome

Many groups of organisms in addition to mammals have Y chromosomes, but these Y chromosomes do not share common ancestry with mammalian Y chromosomes. Such groups include Drosophila

Drosophila

Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...

, some other insects, some fish, some reptiles, and some plants. In Drosophila melanogaster

Drosophila melanogaster

Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...

, the Y chromosome does not trigger male development. Instead, sex is determined by the number of X chromosomes. The D. melanogaster Y chromosome does contain genes necessary for male fertility. So XXY D. melanogaster are female, and D. melanogaster with a single X (X0), are male but sterile. There are some species of Drosophila in which X0 males are both viable and fertile.

ZW chromosomes

Other organisms have mirror image sex chromosomes: the female is "XY" and the male is "XX", but by convention biologists call a "female Y" a W chromosome and the other a Z chromosome. For example, female birds, snakes, and butterflies have ZW sex chromosomes, and males have ZZ sex chromosomes.

External links

Genetic Genealogy: About the use of mtDNA and Y chromosome analysis in ancestry testing
Ensembl genome browser
http://www.ncbi.nlm.nih.gov/mapview/maps.cgi?taxid=9606&chr=Y
Human Genome Project Information—Human Chromosome Y Launchpad
On Topic: Y Chromosome—From the Whitehead Institute for Biomedical Research
Nature—focus on the Y chromosome
National Human Genome Research Institute (NHGRI)—Use of Novel Mechanism Preserves Y chromosome Genes
Ysearch.org – Public Y-DNA database
Y chromosome Consortium (YCC)
NPR's Human Male: Still A Work In Progress

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Overview

Before Y chromosome

Origin

Recombination inhibition

Shrinking

High mutation rate

Inefficient selection

Genetic drift

Gene conversion

Future evolution

Human Y chromosome

Genes

Y chromosome-linked diseases

More common

Defective Y chromosome

XXY

XYY

Rare

More than two Y chromosomes

XX male syndrome

Genetic genealogy

Non-mammal Y chromosome

ZW chromosomes

See also

External links