Citizendia

The Y chromosome is the sex-determining chromosome in most mammals, including humans. A sex-determination system is a biological system that determines the development of sexual characteristics in an Organism. A chromosome is an organized structure of DNA and Protein that is found in cells. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus In mammals, it contains the gene SRY, which triggers testis development, thus determining sex. SRY ( Sex-determining Region Y) is a Sex -determining Gene on the Y chromosome in the Therians (placental mammals and marsupials The testicle (from Latin testiculus, diminutive of testis, meaning "witness" virility plural testes) is the male The human Y chromosome is composed of about 60 million base pairs. In Molecular biology, two Nucleotides on opposite complementary DNA or RNA strands that are connected via Hydrogen bonds are called

Contents

Overview

Most mammals have one pair of sex chromosomes in each cell (though for example the platypus has five pairs). The Platypus ( Ornithorhynchus anatinus) is a semi- aquatic Mammal endemic to eastern Australia, including Tasmania. Males have one Y chromosome and one X chromosome, while females have two X chromosomes. In mammals, the Y chromosome contains the gene that triggers embryonic development as a male. This gene is SRY. SRY ( Sex-determining Region Y) is a Sex -determining Gene on the Y chromosome in the Therians (placental mammals and marsupials Other genes (in addition to SRY) on the Y chromosomes of men and other mammals are needed for normal sperm production. SRY ( Sex-determining Region Y) is a Sex -determining Gene on the Y chromosome in the Therians (placental mammals and marsupials

There are exceptions, however. Among humans, some men have two Xs and a Y ("XXY", see Klinefelter's syndrome), or one X and two Ys (see XYY syndrome), and some women have three Xs or a single X (and no Y, "X0", see Turner syndrome). Klinefelter's syndrome, 47XXY or XXY syndrome is a condition caused by a Chromosome Aneuploidy. XYY syndrome is an Aneuploidy of the Sex chromosomes in which a Human Male receives an extra Y chromosome, producing a 47XYY 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 Turner syndrome or Ullrich-Turner syndrome encompasses several conditions of which monosomy X is the most common There are other exceptions in which SRY is damaged (leading to an XY female), or copied to the X (leading to an XX male). SRY ( Sex-determining Region Y) is a Sex -determining Gene on the Y chromosome in the Therians (placental mammals and marsupials Swyer syndrome, or XY gonadal dysgenesis, is a type of Hypogonadism in which no functional Gonads are present to induce Puberty in an externally XX male syndrome (also called de la Chapelle syndrome) is a rare sex chromosomal disorder For related phenomena see Androgen insensitivity syndrome and Intersex. Androgen insensitivity syndrome (AIS also referred to as androgen resistance syndrome, is a set of disorders of Sexual differentiation caused by Mutations Intersexuality is the state of a living thing of a gonochoristic species whose Sex chromosomes, Genitalia, and/or Secondary sex characteristics

Presence or absence of the Y-chromosome is a method of sexual determination.

Origins and evolution

Before Y-chromosome

Many ectothermic vertebrates have no sex chromosomes. Cold-blooded organisms (called poikilotherms - "of varying temperature" maintain their body temperatures in ways different from Mammals and Birds Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes If they have different sexes, sex is determined environmentally rather than genetically. For some of them, especially reptiles, sex depends on the incubation temperature; others are hermaphroditic (meaning they contain both male and female gametes in the same individual). Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers A hermaphrodite is an organism having both male and female reproductive organs

Origin

The X and Y chromosomes diverged around 300 million years ago from a pair of identical chromosomes[1], termed autosomes, when an ancestral mammal developed an allelic variation, a so-called 'sex locus' - simply possessing this allele caused the organism to be male. An autosome is a non-sex Chromosome. It is an ordinarily paired type of chromosome that is the same in both Sexes of a species. An allele (ˈæliːl (UK /əˈliːl/ (US (from the Greek αλληλος allelos, meaning each other) is one member of a pair or series of different forms [2] 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. In Genetics, a chromosome translocation is a Chromosome abnormality caused by rearrangement of parts between nonhomologous Chromosomes. [3]

Recombination inhibition

Recombination between the X and Y chromosomes proved harmful - it resulted in males without necessary genes formerly found on the X chromosome, and females with unnecessary or even harmful genes previously only found on the Y chromosome. Genetic recombination is the process by which a strand of genetic material (usually DNA; but can also be RNA) is broken and then joined to a different DNA molecule 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[4]. 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

With time, larger and larger areas became unable to recombine with the X chromosome. This caused its own problems: without recombination, the removal of harmful mutations from chromosomes becomes increasingly difficult. These harmful mutations continued to damage Y-unique genes until several finally stopped functioning and became genetic junk; this was eventually removed from the Y chromosome. In Molecular biology, junk DNA is a provisional label for the portions of the DNA sequence of a Chromosome or a Genome for which no

Today, the human Y chromosome itself contains only 86 working genes,[5] compared to close to 1000 working genes on the X chromosome. In some animals, Y degradation is even more severe. The dunnart, a marsupial carrying a 10-12 Mb Y chromosome, has only four characterised genes; among them the SRY gene, is the smallest known mammalian Y chromosome. Dunnarts are furry narrow-footed Marsupials the size of a mouse A megabase (Mb is a unit of length for DNA fragments equal to 1 million Nucleotides In the Human genome, one megabase is roughly equivalent to one SRY ( Sex-determining Region Y) is a Sex -determining Gene on the Y chromosome in the Therians (placental mammals and marsupials [6]

Gene conversion

In 2003, researchers from MIT discovered a process which may slow down the process of degradation. Year 2003 ( MMIII) was a Common year starting on Wednesday of the Gregorian calendar. They found that human Y chromosome is able to "recombine" with itself, using palindrome base pair sequences. A palindrome is a word phrase number or other sequence of units that can be read the same way in either direction (the adjustment of punctuation and spaces between words In Molecular biology, two Nucleotides on opposite complementary DNA or RNA strands that are connected via Hydrogen bonds are called [7] Such a "recombination" is called gene conversion or recombinational loss of heterozygosity (RecLOH). Gene conversion is an event in DNA Genetic recombination, which occurs at high frequencies during meiotic division but which also occurs in somatic cells RecLOH is a term in Genetics that is an abbreviation for " Recombinational Loss of Heterozygosity "

In the case of the Y chromosomes, the palindromes are not junk DNA; these strings of bases contain functioning genes important for male fertility. A palindrome is a word phrase number or other sequence of units that can be read the same way in either direction (the adjustment of punctuation and spaces between words In Molecular biology, junk DNA is a provisional label for the portions of the DNA sequence of a Chromosome or a Genome for which no 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 chimpanzees, bonobos and gorillas. Chimpanzee (often shortened to chimp) is the common name for the two extant Species of Apes in the Genus Pan. The Bonobo (bə'noʊboʊ Pan paniscus) until recently usually called the Pygmy Chimpanzee (and less often the Dwarf or Gracile Chimpanzee Gorillas, the largest of the living Primates are ground-dwelling Herbivores that inhabit the Forests of Africa. 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

After only an SRY (or other sex-determining) gene remains from the whole Y chromosome, there are the following possibilities:

Human Y chromosome

In humans, the Y chromosome spans 58 million base pairs (the building blocks of DNA) and represents approximately 0. In Molecular biology, two Nucleotides on opposite complementary DNA or RNA strands that are connected via Hydrogen bonds are called Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known 38% of the total DNA in a human cell. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called The human Y chromosome contains 86[5] 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 regions at the telomeres (which comprise about 5% of the chromosome's length). The pseudoautosomal regions, PAR1 and PAR3 are homologous sequences of Nucleotides on the X and Y chromosomes The pseudoautosomal A telomere is a region of repetitive DNA at the end of Chromosomes which protects the end of the chromosome from destruction These regions are relics of ancient homology between the X and Y chromosomes. In Evolutionary biology, homology has come to mean any similarity between characters that is due to their shared ancestry. The bulk of the Y chromosome which does not recombine is called the "NRY" or non-recombining region of the Y chromosome. [8] It is the SNPs in this region which are used for tracing direct paternal ancestral lines. A single nucleotide polymorphism ( SNP, pronounced snip) is a DNA sequence variation occurring when a single Nucleotide - A, T

Genes

Y-Chromosome-linked diseases

Y-Chromosome-linked diseases can be of more common types, or very rare ones. Amelogenin is a low-molecular-weight Protein found in developing Tooth enamel, and it belongs to a family of extracellular matrix (ECM proteins Adenine nucleotide translocator ( ANT) also known as the ADP / ATP translocator is a Mitochondrial protein AZF is an acronym for a region on the human male Y chromosome called the AZ oospermia F actor Azoospermia is the Medical condition of a male not having any measurable level of sperm in his Semen. Interleukins are a group of Cytokines (secreted Signaling molecules) that were first seen to be expressed by White blood cells ( Leukocytes hence Ribonucleic acid ( RNA) is a Nucleic acid that consists of a long chain of Nucleotide units SRY ( Sex-determining Region Y) is a Sex -determining Gene on the Y chromosome in the Therians (placental mammals and marsupials The testicle (from Latin testiculus, diminutive of testis, meaning "witness" virility plural testes) is the male A zinc finger protein is a DNA-binding protein domain comprised of Zinc fingers ranging from two in the Drosophila regulator ADR1, the more common 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 50% 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.

Defect Y-chromosome

This results in the person presenting a female phenotype even though that person possesses an XY karyotype (i. A phenotype is any observable characteristic of an Organism, such as its morphology, Development, biochemical or physiological properties A karyotype is the characteristic Chromosome complement of a Eukaryote Species. e. , is born with female-like genitalia). The lack of the second X results in infertility. In other words, viewed from opposite direction, the person goes through defeminization but fails to complete masculinization. Defeminization is a term in developmental Biology, especially Zoology, referring to an aspect of the process of Sexual differentiation by which a potential In biology and medicine virilization refers to the biological development of Sex differences, changes which make a Male body different from a Female body

The cause can be seen as an incomplete Y chromosome: the usual karyotype in these cases is 46X, 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 usually is a girl with the features of Turner syndrome or mixed gonadal dysgenesis. Turner syndrome or Ullrich-Turner syndrome encompasses several conditions of which monosomy X is the most common Mixed gonadal dysgenesis is a condition of unusual and asymmetrical gonadal development leading to an unassigned Sex differentiation.

XXY

Klinefelter's syndrome (47, XXY) is not an aneuploidy of the Y chromosome, but a condition of having an extra X chromosome. Klinefelter's syndrome, 47XXY or XXY syndrome is a condition caused by a Chromosome Aneuploidy. It usually results in defective postnatal testicular function, but as the extra X does not seem to be due to direct interference with expression of Y genes. The mechanism is not fully understood.

XYY
Main article: XYY

It is possible for an abnormal number (aneuploidy) of Y chromosomes to result in problems. XYY syndrome is an Aneuploidy of the Sex chromosomes in which a Human Male receives an extra Y chromosome, producing a 47XYY

47,XYY syndrome is caused by the presence of a single extra copy of the Y chromosome in each of a male's cells. XYY syndrome is an Aneuploidy of the Sex chromosomes in which a Human Male receives an extra Y chromosome, producing a 47XYY 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 occurs when there has been a recombination in the formation of the male gametes, causing the SRY-portion of the Y chromosome to move to the X chromosome. XX male syndrome (also called de la Chapelle syndrome) is a rare sex chromosomal disorder A gamete (from Ancient Greek γαμέτης; translated gamete = wife gametes = husband is a cell that fuses with another gamete SRY ( Sex-determining Region Y) is a Sex -determining Gene on the Y chromosome in the Therians (placental mammals and marsupials 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 (the application of genetics to traditional genealogy) 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. Genetic genealogy is the application of Genetics to traditional genealogy. Genetics (from Ancient Greek grc-Latn genetikos, “genitive” and that from grc-Latn genesis, “origin” a discipline of Biology, is Genealogy (from Greek: el γενεά el-Latn genea, "descent" and el λόγος el-Latn logos, "knowledge" is the study of [9] See www.smgf.org for more information. Mitochondrial DNA, maternally inherited, is used in an analogous way to trace the maternal line. Mitochondrial DNA ( mtDNA) is the DNA located in Organelles called mitochondria.


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, some other insects, some fish, some reptiles, and some plants. Drosophila is a Genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" In Drosophila melanogaster, the Y chromosome does not trigger male development. Drosophila melanogaster (from the Greek for black-bellied dew-lover) is a two-winged insect that belongs to the Diptera, the order 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. The ZW sex-determination system is a system that determines the sex of offspring in Birds, some Fish, and some Insects (including Butterflies The ZW sex-determination system is a system that determines the sex of offspring in Birds, some Fish, and some Insects (including Butterflies For example, female birds, snakes, and butterflies have ZW sex chromosomes, and males have ZZ sex chromosomes.

See also

References

  1. ^ Lahn B, Page D (1999). In Human genetics, a Human Y-chromosome DNA haplogroup is a Haplogroup defined by differences in the non- recombining portions of DNA from the Listed here are notable Ethnic groups by Y-DNA Haplogroups based on relevant studies DYS is short for D NA Y -chromosome S egment and is used to designate a segment of DNA on the Y chromosome where a sequence of The following list of DYS (DNA Y-chromosome Segment markers are commonly used in Genealogical DNA testing DYS454 is the least diverse and multi-copy In human Genetics, Y-chromosomal Adam ( Y- MRCA) is the patrilineal Human Most recent common ancestor (MRCA from whom all Y-chromosomal Aaron is the name given to the hypothesised most recent common ancestor of many of the patrilineal Jewish priestly caste known as Kohanim Genetic genealogy is the application of Genetics to traditional genealogy. A genealogical DNA test examines the Nucleotides at specific locations on a person's DNA for Genetic genealogy purposes A Y-STR is a Short tandem repeat (STR on the Y chromosome. Y-STRs are often designated by DYS numbers. A single nucleotide polymorphism ( SNP, pronounced snip) is a DNA sequence variation occurring when a single Nucleotide - A, T In mammals Y-linkage refers to when a phenotypic trait is determined by an allele (or gene on the Y chromosome. The X chromosome is one of the two sex-determining Chromosomes in many animal species including mammals (the other is the Y chromosome) "Four evolutionary strata on the human X chromosome". Science 286 (5441): 964-7. doi:10.1126/science.286.5441.964. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 10542153.  
  2. ^ Graves J. A. M. (2006). "Sex chromosome specialization and degeneration in mammals". Cell 124 (5): 901-14. doi:10.1016/j.cell.2006.02.024. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 16530039.  
  3. ^ Graves J. A. M. , Koina E. , Sankovic N. (2006). "How the gene content of human sex chromosomes evolved". Curr Opin Genet Dev 16 (3): 219-24. doi:10.1016/j.gde.2006.04.007. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 16650758.  
  4. ^ Graves J. A. M. (2006). "Sex chromosome specialization and degeneration in mammals". Cell 124 (5): 901-14. doi:10.1016/j.cell.2006.02.024. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 16530039.  
  5. ^ a b Ensembl Human MapView release 43 (February 2007). Retrieved on 2007-04-14. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 43 BC - Battle of Forum Gallorum: Mark Antony, besieging Julius Caesar 's assassin Decimus Junius Brutus in
  6. ^ Toder R. , Wakefield M. J. , Graves J. A. M. (2000). "The minimal mammalian Y chromosome - the marsupial Y as a model system". Cytogenet Cell Genet 91 (1-4): 285-92. doi:10.1159/000056858. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 11173870.  
  7. ^ Rozen S, Skaletsky H, Marszalek J, Minx P, Cordum H, Waterston R, Wilson R, Page D (2003). "Abundant gene conversion between arms of palindromes in human and ape Y chromosomes". Nature 423 (6942): 873-6. doi:10.1038/nature01723. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 12815433.  
  8. ^ ScienceDaily.com Apr. 3, 2008
  9. ^ See www.smgf.org for more information.

External links

Dictionary

Y chromosome

-noun

  1. (genetics) A mammalian sex chromosome, occurring only in male cells. Cells of females have a pair of X chromosomes while cells of males have an X and a Y.
© 2009 citizendia.org; parts available under the terms of GNU Free Documentation License, from http://en.wikipedia.org