Misplaced Pages

#382617

92-551: 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, the Y chromosome contains the SRY gene, which triggers development of male gonads . The Y chromosome

184-461: A cohors (plural cohortes ). Some of the plant families still retain the names of Linnaean "natural orders" or even the names of pre-Linnaean natural groups recognized by Linnaeus as orders in his natural classification (e.g. Palmae or Labiatae ). Such names are known as descriptive family names. In the field of zoology , the Linnaean orders were used more consistently. That is,

276-418: A Y chromosome in males. Females therefore have 23 homologous chromosome pairs, while males have 22. The X and Y chromosomes have small regions of homology called pseudoautosomal regions . An X chromosome is always present as the 23rd chromosome in the ovum , while either an X or Y chromosome may be present in an individual sperm . Early in female embryonic development, in cells other than egg cells, one of

368-402: 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

460-511: A WZ system. Some gymnosperms, such as Johann's Pine ( Pinus johannis ), have homomorphic sex chromosomes that are almost indistinguishable through karyotyping . Cosexual angiosperms with either monoecious or hermaphroditic flowers do not have sex chromosomes. Angiosperms with separate sexes (dioecious) may use sex chromosomes or environmental flowers for sex determination. Cytogenetic data from about 100 angiosperm species showed heteromorphic sex chromosomes in approximately half, mostly taking

552-408: A Y chromosome from their father. It is thus the male's sperm that determines the sex of each offspring in such species. However, a small percentage of humans have a divergent sexual development, known as intersex . This can result from allosomes that are neither XX nor XY. It can also occur when two fertilized embryo fuse, producing a chimera that might contain two different sets of DNA one XX and

644-473: 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

736-566: A chromosome survey of 315 male patients at Scotland 's only special security hospital for the developmentally disabled , finding a higher than expected number of patients to have an extra Y chromosome. The authors of this study wondered "whether an extra Y chromosome predisposes its carriers to unusually aggressive behaviour", and this conjecture "framed the next fifteen years of research on the human Y chromosome". Sex chromosome Nettie Stevens and Edmund Beecher Wilson both independently discovered sex chromosomes in 1905. However, Stevens

828-570: A distinct rank of biological classification having its own distinctive name (and not just called a higher genus ( genus summum )) was first introduced by the German botanist Augustus Quirinus Rivinus in his classification of plants that appeared in a series of treatises in the 1690s. Carl Linnaeus was the first to apply it consistently to the division of all three kingdoms of nature (then minerals , plants , and animals ) in his Systema Naturae (1735, 1st. Ed.). For plants, Linnaeus' orders in

920-470: A group of related families. What does and does not belong to each order is determined by a taxonomist , as is whether a particular order should be recognized at all. Often there is no exact agreement, with different taxonomists each taking a different position. There are no hard rules that a taxonomist needs to follow in describing or recognizing an order. Some taxa are accepted almost universally, while others are recognized only rarely. The name of an order

1012-410: 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

SECTION 10

#1732766214383

1104-417: 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

1196-441: 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

1288-457: 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 ,

1380-423: 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

1472-460: 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

1564-563: 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

1656-466: 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

1748-420: 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

1840-439: 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

1932-454: Is a process defined as when the type of the sex chromosome changes as a product of a change in the identity of the sex-determining genes (such as by mutation) or by a change in their location. In other cases, sex chromosomes may grow substantially with respect to their ancestral forms as a result of fusion events with autosomes, and autosome-sex chromosome fusions result in what are called neo-sex chromosomes. Five examples of this are now known in

SECTION 20

#1732766214383

2024-500: 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:

2116-434: Is also used as model for the study of sex chromosomes evolution. Based on the phylogenetic topology distribution there are three regions on sex chromosomes. One region that stops recombining in the ancestor of H. lupulus , second that stops recombining in modern H. lupulus and the third region called pseudoautosomal region. H. lupulus is the rare case in plants in which Y is smaller than X, while its ancestor plant has

2208-795: 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

2300-467: Is credited for discovering them earlier than Wilson. In humans, each cell nucleus contains 23 pairs of chromosomes, a total of 46 chromosomes. The first 22 pairs are called autosomes . Autosomes are homologous chromosomes i.e. chromosomes which contain the same genes (regions of DNA) in the same order along their chromosomal arms. The 23rd pair of chromosomes are called allosomes. These consist of two X chromosomes in females, and an X chromosome and

2392-442: 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

2484-399: Is determined in a single XY system. In a more complicated system, the sandalwood species Viscum fischeri has X1X1X2X2 chromosomes in females, and X1X2Y chromosomes in males. Amplification of transposable elements, tandom repeats especially accumulation of long tandom repeats ( LTR ) retrotransposones are responsible for plant sex chromosome evolution. The insertion of retrotransposons

2576-502: Is estimated to have arisen only 4000 years ago, post-domestication of the plant. The genetic architecture suggests that either the Y chromosome has an X-inactivating gene, or that the Y chromosome has an X-activating gene. Allosomes not only carry the genes that determine male and female traits, but also those for some other characteristics as well. Genes that are carried by either sex chromosome are said to be sex linked . Sex linked diseases are passed down through families through one of

2668-566: 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

2760-420: 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

2852-607: 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 ,

Y chromosome - Misplaced Pages Continue

2944-486: Is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy . It is classified between family and class . In biological classification , the order is a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes . An immediately higher rank, superorder , is sometimes added directly above order, with suborder directly beneath order. An order can also be defined as

3036-440: 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 the smaller chromosome (now labelled "Y")

3128-720: Is probably the major cause of y-chromosome expansion and plant genome size evolution. Retrotransposones contribute in size determination of sex chromosomes and its proliferation varies even in closely related species. LTR and tandom repeats play dominant role in the evolution of S. latifolia sex chromosomes. Athila is new family of retroelements, discovered in Arabidopsis thaliana , present in heterochromatin region only. Athila retroelements overrepresented in X but absent in Y while tandem repeats enriched in Y-chromosome. Some chloroplast sequences have also been identified in

3220-557: Is reflected in their sex-determination systems, which include XY and UV systems as well as many variants. Sex chromosomes have evolved independently across many plant groups. Recombination of chromosomes may lead to heterogamety before the development of sex chromosomes, or recombination may be reduced after sex chromosomes develop. Only a few pseudoautosomal regions normally remain once sex chromosomes are fully differentiated. When chromosomes do not recombine, neutral sequence divergences begin to accumulate, which has been used to estimate

3312-418: 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

3404-593: 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,

3496-533: Is usually written with a capital letter. For some groups of organisms, their orders may follow consistent naming schemes . Orders of plants , fungi , and algae use the suffix -ales (e.g. Dictyotales ). Orders of birds and fishes use the Latin suffix -iformes meaning 'having the form of' (e.g. Passeriformes ), but orders of mammals and invertebrates are not so consistent (e.g. Artiodactyla , Actiniaria , Primates ). For some clades covered by

3588-444: Is when both matching genes must be abnormal to cause disease. If only one gene in the pair is abnormal, the disease does not occur, or is mild. Someone who has one abnormal gene (but no symptoms) is called a carrier. A carrier can pass this abnormal gene to his or her children. X chromosome carry about 1500 genes, more than any other chromosome in the human body. Most of them code for something other than female anatomical traits. Many of

3680-528: The International Code of Zoological Nomenclature , several additional classifications are sometimes used, although not all of these are officially recognized. In their 1997 classification of mammals , McKenna and Bell used two extra levels between superorder and order: grandorder and mirorder . Michael Novacek (1986) inserted them at the same position. Michael Benton (2005) inserted them between superorder and magnorder instead. This position

3772-815: The Systema Naturae and the Species Plantarum were strictly artificial, introduced to subdivide the artificial classes into more comprehensible smaller groups. When the word ordo was first consistently used for natural units of plants, in 19th-century works such as the Prodromus Systematis Naturalis Regni Vegetabilis of Augustin Pyramus de Candolle and the Genera Plantarum of Bentham & Hooker, it indicated taxa that are now given

Y chromosome - Misplaced Pages Continue

3864-551: 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

3956-462: 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

4048-533: The DNA and prevents expression of most genes. This compaction is regulated by PRC2 (Polycomb Repressive Complex 2). All diploid organisms with allosome-determined sex get half of their allosomes from each of their parents. In most mammals, females are XX, and can pass along either of their Xs; since males are XY they can pass along either an X or a Y. Females in such species receive an X chromosome from each parent while males receive an X chromosome from their mother and

4140-414: 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

4232-401: The X chromosomes is randomly and permanently partially deactivated : In some cells, the X chromosome inherited from the mother deactivates; in other cells, it is the X chromosome inherited from the father. This ensures that both sexes always have exactly one functional copy of an X chromosome in each body cell. The deactivated X chromosome is silenced by repressive heterochromatin that compacts

4324-504: The X or Y chromosomes. Since usually men inherit Y chromosomes, they are the only ones to inherit Y-linked traits. Men and women can get the X-linked ones since both inherit X chromosomes. An allele is either said to be dominant or recessive . Dominant inheritance occurs when an abnormal gene from one parent causes disease even though the matching gene from the other parent is normal. The abnormal allele dominates. Recessive inheritance

4416-575: The XX pair during meiosis . Diverse mechanisms are involved in the determination of sex in animals. For mammals, sex determination is carried by the genetic contribution of the spermatozoon. Many lower chordates, such as fish, amphibians and reptiles, have systems that are influenced by the environment. Fish and amphibians, for example, have genetic sex determination but their sex can also be influenced by externally available steroids and incubation temperature of eggs. In some reptiles, e.g. sea turtles , only

4508-666: 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

4600-440: 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

4692-476: 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

SECTION 50

#1732766214383

4784-481: 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

4876-406: 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

4968-455: 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

5060-471: 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

5152-696: The Y-chromosome of S. latifolia . S. vulgaris has more retroelements in their sex chromosomes compare to S. latifolia . Microsatellite data shows that there is no significant difference between X and Y-chromosome microsatellites in both Silene species. This would conclude that microsatellites do not participate in Y-chromosome evolution. The portion of Y-chromosome that never recombine with X-chromosome faces selection reduction. This reduced selection leads to insertion of transposable elements and accumulation of deleterious mutation . The Y become larger and smaller than X due to insertion of retroelement and deletion of genetic material respectively. The genus Humulus

5244-460: The age of sex chromosomes in various plant lineages. Even the oldest estimated divergence, in the liverwort Marchantia polymorpha , is more recent than mammal or bird divergence. Due to this recency, most plant sex chromosomes also have relatively small sex-linked regions. Current evidence does not support the existence of plant sex chromosomes more ancient than those of M. polymorpha . The high prevalence of autopolyploidy in plants also impacts

5336-454: 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

5428-477: The autosomes. There is variation even within this system, including UU/V and U/VV chromosome arrangements. In some bryophytes, microchromosomes have been found to co-occur with sex chromosomes and likely impact sex determination. Dioecy is common among gymnosperms , found in an estimated 36% of species. However, heteromorphic sex chromosomes are relatively rare, with only five species known as of 2014. Five of these use an XY system, and one ( Ginkgo biloba ) uses

5520-596: The bryophytes, including liverworts, hornworts and mosses, sex chromosomes are common. The sex chromosomes in bryophytes affect what type of gamete is produced by the gametophyte, and there is wide diversity in gametophyte type. Unlike seed plants, where gametophytes are always unisexual, in bryophytes they may produce male, female, or both types of gamete. Bryophytes most commonly employ a UV sex-determination system, where U produces female gametophytes and V produces male gametophytes. The U and V chromosomes are heteromorphic with U larger than V and are frequently both larger than

5612-412: 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 the fact that the disappearance of the Y chromosome

SECTION 60

#1732766214383

5704-492: 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

5796-527: The form of XY sex-determination systems. Their Y is typically larger, unlike in humans; however there is diversity among angiosperms. In the Poplar genus ( Populus ) some species have male heterogamety while others have female heterogamety. Sex chromosomes have arisen independently multiple times in angiosperms, from the monoecious ancestral condition. The move from a monoecious to dioecious system requires both male and female sterility mutations to be present in

5888-469: 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 the ancestral sex chromosomes and autosomes . Modern data cast doubt on

5980-414: 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

6072-532: 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

6164-426: 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

6256-446: 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 the Y chromosome, such as most species of Nematodes. However, in order for

6348-548: The incubation temperature determines sex ( temperature-dependent sex determination ). Many scientists argue that sex determination in plants is more complex than that in humans. This is because even flowering plants have a variety of mating systems, their sex determination primarily regulated by MADS-box genes. These genes code for proteins that form the sex organs in flowers. Plant sex chromosomes are most common in bryophytes , relatively common in vascular plants and unknown in ferns and lycophytes . The diversity of plants

6440-462: 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

6532-437: 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)

6624-403: The non-sex determining X-linked genes are responsible for abnormal conditions. The Y chromosome carries about 78 genes. Most of the Y chromosome genes are involved with essential cell house-keeping activities and sperm production. Only one of the Y chromosome genes, the SRY gene, is responsible for male anatomical traits. When any of the 9 genes involved in sperm production are missing or defective

6716-708: The orders in the zoology part of the Systema Naturae refer to natural groups. Some of his ordinal names are still in use, e.g. Lepidoptera (moths and butterflies) and Diptera (flies, mosquitoes, midges, and gnats). In virology , the International Committee on Taxonomy of Viruses 's virus classification includes fifteen taxomomic ranks to be applied for viruses , viroids and satellite nucleic acids : realm , subrealm , kingdom , subkingdom, phylum , subphylum , class, subclass, order, suborder, family, subfamily , genus, subgenus , and species. There are currently fourteen viral orders, each ending in

6808-507: 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

6900-548: The other XY. It could also result from exposure, often in utero, to chemicals that disrupt the normal conversion of the allosomes into sex hormones and further into the development of either ambiguous outer genitalia or internal organs . There is a gene in the Y chromosome that has regulatory sequences that control genes that code for maleness, called the SRY gene . This gene produces a testis-determining factor ("TDF"), which initiates testis development in humans and other mammals. The SRY sequence's prominence in sex determination

6992-442: The population. Male sterility likely arises first as an adaptation to prevent selfing. Once male sterility has reached a certain prevalence, then female sterility may have a chance to arise and spread. In the domesticated papaya ( Carica papaya ), three sex chromosomes are present, denoted as X, Y and Y . This corresponds with three sexes: females with XX chromosomes, males with XY, and hermaphrodites with XY . The hermaphrodite sex

7084-564: The precursor of the currently used International Code of Nomenclature for algae, fungi, and plants . In the first international Rules of botanical nomenclature from the International Botanical Congress of 1905, the word family ( familia ) was assigned to the rank indicated by the French famille , while order ( ordo ) was reserved for a higher rank, for what in the 19th century had often been named

7176-502: The rank of family (see ordo naturalis , ' natural order '). In French botanical publications, from Michel Adanson 's Familles naturelles des plantes (1763) and until the end of the 19th century, the word famille (plural: familles ) was used as a French equivalent for this Latin ordo . This equivalence was explicitly stated in the Alphonse Pyramus de Candolle 's Lois de la nomenclature botanique (1868),

7268-404: The result is usually very low sperm counts and infertility. Examples of mutations on the X chromosome include more common diseases such as the following: Other complications include: Sex chromosomes evolve from standard pairs of autosomal chromosomes. In a large number of organisms, the sex-determination systems presently observed are products of sex chromosome turnover. Sex chromosome turnover

7360-455: 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

7452-468: 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

7544-410: 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

7636-406: The same size of both X and Y chromosomes. This size difference should be caused by deletion of genetic material in Y but that is not the case. This is because of complex dynamics like the larger size of X than Y-chromosome may be due to duplication or retrotransposition and size of Y remains same. Ferns and lycophytes have bisexual gametophytes , so there is no evidence for sex chromosomes. In

7728-472: The songbird superfamily Sylvioidea . There is one experimentally documented case of sex chromosome turnover occurring during a 30-year evolutionary experiment involving teleost fish (specifically the swordtails ), in which hybridization experiments resulted in a translocation of the sex-determiner region of a sex chromosome into an autosome. This resulted in the autosome becoming a novel W sex chromosome. Order (biology) Order ( Latin : ordo )

7820-426: 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

7912-413: The structure of their sex chromosomes. Polyploidization can occur before and after the development of sex chromosomes. If it occurs after sex chromosomes are established, dosage should stay consistent between the sex chromosomes and autosomes, with minimal impact on sex differentiation. If it occurs before sex chromosomes become heteromorphic, as is likely in the octoploid red sorrel Rumex acetosella , sex

8004-488: 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)

8096-418: Was adopted by Systema Naturae 2000 and others. In botany , the ranks of subclass and suborder are secondary ranks pre-defined as respectively above and below the rank of order. Any number of further ranks can be used as long as they are clearly defined. The superorder rank is commonly used, with the ending -anae that was initiated by Armen Takhtajan 's publications from 1966 onwards. The order as

8188-506: 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

8280-447: Was discovered when the genetics of sex-reversed XX men (i.e. humans who possess biological male-traits but actually have XX allosomes) were studied. After examination, it was discovered that the difference between a typical XX individual (traditional female) and a sex-reversed XX man was that the typical individuals lacked the SRY gene. It is theorized that in sex-reversed XX men, the SRY mistakenly gets translocated to an X chromosome in

8372-399: 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

8464-475: 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

#382617