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60-464: Bearing the surname often (although not always) indicates that one's patrilineal ancestors were priests in the Temple of Jerusalem . Although not all Kohenic lines stem from Aaron , the brother of Moses , he is generally regarded as the patriarch of the lineage and the first Kohen. A single such priest was known as a Kohen, and the hereditary caste descending from these priests is collectively known as

120-537: A genealogical DNA test associated with the Cohen Modal Haplotype (see Y-chromosomal Aaron ). Patrilineality Patrilineality , also known as the male line , the spear side or agnatic kinship , is a common kinship system in which an individual's family membership derives from and is recorded through their father's lineage. It generally involves the inheritance of property, rights, names, or titles by persons related through male kin. This

180-402: A "recombination" is called gene conversion . In the case of the Y chromosomes, the palindromes are not noncoding DNA ; these strings of nucleotides 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

240-478: A chain is formed during mitosis . The first X chromosome in the chain is also partially homologous with the last Y chromosome, indicating that profound rearrangements, some adding new pieces from autosomes, have occurred in history. Platypus sex chromosomes have strong sequence similarity with the avian Z chromosome , indicating close homology , and the SRY gene so central to sex-determination in most other mammals

300-413: A human Y chromosome was shown to contain 62,460,029 base pairs and 41 additional genes . This added 30 million base pairs, but it was discovered that the Y chromosome can vary a lot in size between individuals, from 45.2 million to 84.9 million base pairs. Since almost half of the human Y sequence was unknown before 2022, it could not be screened out as contamination in microbial sequencing projects. As

360-418: A lower bound on the total number of human protein-coding genes. In general, the human Y chromosome is extremely gene poor—it is one of the largest gene deserts in the human genome. Disregarding pseudoautosomal genes, genes encoded on the human Y chromosome include: Diseases linked to the Y chromosome typically involve an aneuploidy , an atypical number of chromosomes. Males can lose the Y chromosome in

420-442: 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. In 1965 and 1966 Patricia Jacobs and colleagues published

480-458: A male. The Y chromosomes of humans and other mammals also contain other genes needed for normal sperm production. There are exceptions, however. Among humans, some males are born two Xs and a Y ("XXY", see Klinefelter syndrome ), one X and two Ys (see XYY syndrome ). Some females have three Xs ( Trisomy X ), and some have a single X instead of two Xs ("X0", see Turner syndrome ). There are other variations in which, during embryonic development ,

540-426: A rate of genetic loss of 4.6 genes per million years. Continued loss of genes at the rate of 4.6 genes per million years would result in a Y chromosome with no functional genes – that is the Y chromosome would lose complete function – within the next 10 million years, or half that time with the current age estimate of 160 million years. Comparative genomic analysis reveals that many mammalian species are experiencing

600-461: A result, the NCBI RefSeq bacterial genome database mistakenly includes some Y chromosome data. The human Y chromosome is normally unable to recombine with the X chromosome, except for small pieces of pseudoautosomal regions (PARs) at the telomeres (which comprise about 5% of the chromosome's length). These regions are relics of ancient homology between the X and Y chromosomes. The bulk of

660-566: A shorter life expectancy. In many cases, a cause and effect relationship between the Y chromosome and health outcomes has not been determined, and some propose loss of the Y chromosome could be a "neutral karyotype related to normal aging ". However, a 2022 study showed that mosaic loss of the Y chromosome causally contributes to fibrosis , heart risks , and mortality. Further studies are needed to understand how mosaic Y chromosome loss may contribute to other sex differences in health outcomes, such as how male smokers have between 1.5 and 2 times

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720-468: A similar loss of function in their heterozygous sex chromosome. Degeneration may simply be the fate of all non-recombining sex chromosomes, due to three common evolutionary forces: high mutation rate , inefficient selection , and genetic drift . With a 30% difference between humans and chimpanzees, the Y chromosome is one of the fastest-evolving parts of the human genome . However, these changes have been limited to non-coding sequences and comparisons of

780-424: A subset of cells, known as mosaic loss. Mosaic loss is strongly associated with age, and smoking is another important risk factor for mosaic loss. Mosaic loss may be related to health outcomes, indicating that the Y chromosome plays important roles outside of sex determination. Males with a higher percentage of hematopoietic stem cells lacking the Y chromosome have a higher risk of certain cancers and have

840-439: 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

900-597: Is a priest or Levite, and the members of all the Twelve Tribes are called Israelites because their father is Israel ( Jacob ). In the first lines of the New Testament , the descent of Jesus Christ from King David is counted through the male lineage. Patrilineal or agnatic succession gives priority to or restricts inheritance of a throne or fief to male heirs descended from the original title holder through males only. Traditionally, agnatic succession

960-502: Is also known to be present in a significant number of men with reduced fertility or reduced sperm count. This results in the person presenting a female phenotype (i.e., is born with female-like genitalia) even though that person possesses an XY karyotype . The lack of the second X results in infertility. In other words, viewed from the opposite direction, the person goes through defeminization but fails to complete masculinization . The cause can be seen as an incomplete Y chromosome:

1020-801: Is apparently not involved in platypus sex-determination. The human Y chromosome is composed of about 62 million base pairs of DNA , making it similar in size to chromosome 19 and represents almost 2% of the total DNA in a male cell . The human Y chromosome carries 693 genes , 107 of which are protein-coding . However, some genes are repeated, making the number of exclusive protein-coding genes just 42. The Consensus Coding Sequence (CCDS) Project only classifies 63 out of 107 genes, though CCDS estimates are often considered lower bounds due to their conservative classification strategy. All single-copy Y-linked genes are hemizygous (present on only one chromosome) except in cases of aneuploidy such as XYY syndrome or XXYY syndrome . Traits that are inherited via

1080-663: Is applied in determining the names and membership of European dynasties . The prevalent forms of dynastic succession in Europe, Asia and parts of Africa were male-preference primogeniture , agnatic primogeniture , or agnatic seniority until after World War II . The agnatic succession model, also known as Salic law , meant the total exclusion of women as hereditary monarchs and restricted succession to thrones and inheritance of fiefs or land to men in parts of medieval and later Europe. This form of strict agnatic inheritance has been officially revoked in all extant European monarchies except

1140-443: Is determined environmentally rather than genetically. For some species, especially reptiles , sex depends on the incubation temperature. Some vertebrates are hermaphrodites , though hermaphroditic species are most commonly sequential , meaning the organism switches sex, producing male or female gametes at different points in its life, but never producing both at the same time. This is opposed to simultaneous hermaphroditism, where

1200-567: Is flawed and suggest that the current human Y chromosome is either no longer shrinking or is shrinking at a much slower rate than the 4.6 genes per million years estimated by the linear extrapolation model. 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 , which undergo multiple cell divisions during gametogenesis . Each cellular division provides further opportunity to accumulate base pair mutations. Additionally, sperm are stored in

1260-421: Is not an aneuploidy 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; it does not seem to be due to direct interference by the extra X with expression of Y genes. 47, XYY syndrome (simply known as XYY syndrome) is caused by the presence of a single extra copy of the Y chromosome in each of

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1320-463: Is sometimes distinguished from cognate kinship, through the mother's lineage, also called the spindle side or the distaff side. A patriline ("father line") is a person's father, and additional ancestors, as traced only through males. In the Bible , family and tribal membership appears to be transmitted through the father. For example, a person is considered to be a priest or Levite , if his father

1380-419: Is the entropy rate of the Y chromosome. Whereas all other chromosomes in the human genome 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. From the definition of entropy rate , the Y chromosome has a much lower information content relative to its overall length, and is more redundant. Even if

1440-594: Is the conservation of the integrity of the genome, a proposal consistent with the idea that meiosis is an adaptation for repairing DNA damage . Without the ability to recombine during meiosis , the Y chromosome is unable to expose individual alleles to natural selection. Deleterious alleles are allowed to "hitchhike" with beneficial neighbors, thus propagating maladapted alleles into 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,

1500-409: Is the patrilineal most recent common ancestor from whom all Y-DNA in living men is descended. An identification of a very rare and previously unknown Y-chromosome variant in 2012 led researchers to estimate that Y-chromosomal Adam lived 338,000 years ago (237,000 to 581,000 years ago with 95% confidence ), judging from molecular clock and genetic marker studies. Before this discovery, estimates of

1560-597: The Kohanim . As multiple languages were acquired through the Jewish diaspora , the surname acquired dozens of variants . Not all persons with related surnames are kohanim, and not all kohanim have related surnames. Some Kohanim have added a secondary appellation to their surname, so as to distinguish themselves from other Kohanim—such as Cohen-Scali of Morocco, who trace their lineage to Zadok , and Cohen-Maghari (Meguri) of Yemen, who trace their lineage to Jehoiarib , one of

1620-523: The Principality of Liechtenstein . By the 21st century, most ongoing European monarchies had replaced their traditional agnatic succession with absolute primogeniture , meaning that the first child born to a monarch inherits the throne, regardless of the child's sex. The fact that human Y-chromosome DNA (Y-DNA) is paternally inherited enables patrilines and agnatic kinships of men to be traced through genetic analysis. Y-chromosomal Adam (Y-MRCA)

1680-555: The WNT4 gene is activated and/or the SRY gene is damaged leading to birth of an XY female (Swyer syndrome ). A Y chromosome may also be present but fail to result in the development of a male phenotype in individuals with androgen insensitivity syndrome , instead resulting in a female or ambiguous phenotype. In other cases, the SRY gene is copied to the X, leading to birth of an XX male . Many ectothermic vertebrates have no sex chromosomes. If these species have different sexes, sex

1740-465: The platypus genome suggested that the XY sex-determination system would not have been present more than 166 million years ago, when monotremes split from other mammals. This re-estimation 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 not present on the autosomes of platypus and birds. The older estimate

1800-427: The priestly divisions . Being a Kohen imposes some limitations: by Jewish law a Kohen may not marry a divorced woman, and may not marry a proselyte (someone who converted to Judaism). Nor should an observant Kohen come into contact with the dead or enter a cemetery unless for the death of a close relative. An effort to test whether people named 'Cohen' actually have a common genetic origin has been undertaken, using

1860-415: The X and Y is still possible. Because the male specific region is very small and contains no essential genes, it is even possible to artificially induce XX males and YY females to no ill effect. Monotremes like platypuses possess four or five pairs of XY sex chromosomes, each pair consisting of sex chromosomes with homologous regions. The chromosomes of neighboring pairs are partially homologous, such that

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1920-668: The Y chromosome are called Y-linked traits, or holandric traits (from Ancient Greek ὅλος hólos , "whole" + ἀνδρός andrós , "male"). At the end of the Human Genome Project (and after many updates) almost half of the Y chromosome remained un-sequenced even in 2021; a different Y chromosome from the HG002 (GM24385) genome was completely sequenced in January 2022 and is included in the new "complete genome" human reference genome sequence, CHM13. The complete sequencing of

1980-550: The Y chromosome contains the SRY gene, which triggers development of male gonads . The Y chromosome is passed only from male parents to male offspring. The Y chromosome was identified as a sex-determining chromosome by Nettie Stevens at Bryn Mawr College in 1905 during a study of the mealworm Tenebrio molitor . Edmund Beecher Wilson independently discovered the same mechanisms the same year, working with Hemiptera . Stevens proposed that chromosomes always existed in pairs and that

2040-441: 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. Other organisms have mirror image sex chromosomes: where

2100-478: The Y chromosome from recombination and cause issues such as infertility. The lack of recombination across the majority of the Y chromosome makes it a useful tool in studying human evolution , since recombination complicates the mathematical models used to trace ancestries. By one estimate, the human Y chromosome has lost 1,393 of its 1,438 original genes over the course of its existence, and linear extrapolation of this 1,393-gene loss over 300 million years gives

2160-483: 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

2220-408: The Y chromosome, during mitosis , has two very short branches which can look merged under the microscope and appear as the descender of a Y-shape. Most therian mammals have only one pair of sex chromosomes in each cell. Males have one Y chromosome and one X chromosome , while females have two X chromosomes. In mammals, the Y chromosome contains a gene, SRY , which triggers embryonic development as

2280-436: The Y chromosome, such as most species of Nematodes. However, in order for the complete elimination of Y to occur, it was necessary to develop an alternative way of determining sex (for example, by determining sex by the ratio of the X chromosome to autosomes), and any genes necessary for male function had to be moved to other chromosomes. In the meantime, modern data demonstrate the complex mechanisms of Y chromosome evolution and

2340-456: The Y chromosome, which does not recombine, is called the "NRY", or non-recombining region of the Y chromosome. Single-nucleotide polymorphisms (SNPs) in this region are used to trace direct paternal ancestral lines. More specifically, PAR1 is at 0.1–2.7 Mb. PAR2 is at 56.9–57.2 Mb. The non-recombining region (NRY) or male-specific region (MSY) sits between. Their sizes is now known perfectly from CHM13: 2.77 Mb and 329.5 kb. Until CHM13

2400-472: 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 into 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

2460-457: The alternate route of crossover recombination. The Y-Y gene conversion rate in humans is about 1.52 x 10 conversions/base/year. These gene conversion events may reflect a basic function of meiosis, that of conserving the integrity of the genome. According to some theories, in the terminal stages of the degeneration of the Y chromosome, other chromosomes may increasingly take over genes and functions formerly associated with it and finally, within

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2520-511: The ancestral sex chromosomes and autosomes . Modern data cast doubt on the hypothesis that the Y-chromosome will disappear. This conclusion was reached by scientists who studied the Y chromosomes of rhesus monkeys. When genomically comparing the Y chromosome of rhesus monkeys and humans, scientists found very few differences, given that humans and rhesus monkeys diverged 30 million years ago. Outside of mammals, some organisms have lost

2580-493: The data in PAR1 and PAR2 was just copied over from X chromosome. The following are some of the gene count estimates of human Y chromosome. Because researchers use different approaches to genome annotation their predictions of the number of genes on each chromosome varies (for technical details, see gene prediction ). Among various projects, CCDS takes an extremely conservative strategy. So CCDS's gene number prediction represents

2640-532: The date when Y-chromosomal Adam lived were much more recent, estimated to be tens of thousands of years. Y chromosome The Y chromosome is one of two sex chromosomes in therian mammals and other organisms . Along with the X chromosome , it is part of the XY sex-determination system , in which the Y is the sex-determining chromosome because the presence of the Y chromosome causes offspring produced in sexual reproduction to be of male sex . In mammals,

2700-660: The fact that the disappearance of the Y chromosome is not guaranteed. Fisher's principle outlines why almost all species using sexual reproduction have a sex ratio of 1:1. W. D. Hamilton gave the following basic explanation in his 1967 paper on "Extraordinary sex ratios", given the condition that males and females cost equal amounts to produce: Many groups of organisms in addition to therian mammals have Y chromosomes, but these Y chromosomes do not share common ancestry with therian Y chromosomes. Such groups include monotremes, Drosophila , some other insects, some fish, some reptiles, and some plants. In Drosophila melanogaster ,

2760-399: The framework of this theory, the Y chromosome disappears entirely, and a new sex-determining system arises. Several species of rodent in the sister families Muridae and Cricetidae have reached a stage where the XY system has been modified, in the following ways: Outside of the rodents, the black muntjac , Muntiacus crinifrons , evolved new X and Y chromosomes through fusions of

2820-416: The highly oxidative environment of the testis , which encourages further mutation. These two conditions combined put the Y chromosome at a greater opportunity of mutation than the rest of the genome. The increased mutation opportunity for the Y chromosome is reported by Graves as a factor 4.8. However, her original reference obtains this number for the relative mutation rates in male and female germ lines for

2880-536: The homogeneous sex is the male, with two Z chromosomes, and the female is the heterogeneous sex with a Z chromosome and a W chromosome. For example, the ZW sex-determination system is found in birds , snakes , and butterflies ; the females have ZW sex chromosomes, and males have ZZ sex chromosomes. There are some species, such as the Japanese rice fish , in which the XY system is still developing and cross over between

2940-428: The human and chimpanzee Y chromosomes (first published in 2005) show that the human Y chromosome has not lost any genes since the divergence of humans and chimpanzees between 6–7 million years ago. Additionally, a scientific report in 2012 stated that only one gene had been lost since humans diverged from the rhesus macaque 25 million years ago. These facts provide direct evidence that the linear extrapolation model

3000-463: 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 . The comparison demonstrated that

3060-439: The lineage leading to humans. The observation that the Y chromosome experiences little meiotic recombination and has an accelerated rate of mutation and degradative change compared to the rest of the genome suggests an evolutionary explanation for the adaptive function of meiosis with respect to the main body of genetic information. Brandeis proposed that the basic function of meiosis (particularly meiotic recombination)

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3120-510: 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 that were beneficial for males and harmful to (or had no effect on) females either developed on the Y chromosome or were acquired by the Y chromosome through the process of translocation . Until recently, the X and Y chromosomes in mammals were thought to have diverged around 300 million years ago. However, research published in 2008 analyzing

3180-460: The risk of non-respiratory cancers as female smokers. Potential countermeasures identified so far include not smoking or stopping smoking and at least one potential drug that "may help counteract the harmful effects of the chromosome loss" is under investigation. Y chromosome microdeletion (YCM) is a family of genetic disorders caused by missing genes in the Y chromosome. Many affected men exhibit no symptoms and lead normal lives. However, YCM

3240-471: The same organism produces male and female gametes at the same time. Most simultaneous hermaphrodite species are invertebrates, and among vertebrates, simultaneous hermaphroditism has only been discovered in a few orders of fish. The X and Y chromosomes are thought to have evolved from a pair of identical chromosomes, termed autosomes , when an ancestral animal developed an allelic variation (a so-called "sex locus") and simply possessing this allele caused

3300-412: 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. Gene conversion tracts formed during meiosis are long, about 2,068 base pairs, and significantly biased towards the fixation of G or C nucleotides (GC biased). The recombination intermediates preceding gene conversion were found to rarely take

3360-518: The smaller chromosome (now labelled "Y") was the pair of the X chromosome discovered in 1890 by Hermann Henking . She realized that the previous idea of Clarence Erwin McClung , that the X chromosome determines sex, was wrong and that sex determination is, in fact, due to the presence or absence of the Y chromosome. In the early 1920s, Theophilus Painter determined that X and Y chromosomes determined sex in humans (and other mammals). The chromosome

3420-428: The species-wide degeneration of Y chromosomes through Muller's ratchet . As has been already mentioned, the Y chromosome is unable to recombine during meiosis like the other human chromosomes; however, 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 base pair sequences. Such

3480-488: The usual karyotype in these cases is 45X, 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 or mixed gonadal dysgenesis . Klinefelter syndrome (47, XXY)

3540-512: Was based on erroneous reports that the platypus X chromosomes contained these sequences. Most chromosomes recombine during meiosis. However, in males, the X and Y pair in a shared region known as the pseudoautosomal region (PAR). The PAR undergoes frequent recombination between the X and Y chromosomes, but recombination is suppressed in other regions of the Y chromosome. These regions contain sex-determining and other male-specific genes. Without this suppression, these genes could be lost from

3600-401: Was given the name "Y" simply to follow on from Henking's "X" alphabetically. The idea that the Y chromosome was named after its similarity in appearance to the letter "Y" is mistaken. All chromosomes normally appear as an amorphous blob under the microscope and only take on a well-defined shape during mitosis . This shape is vaguely X-shaped for all chromosomes. It is entirely coincidental that

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