Y chromosome determines the sex of an individualSex chromosomeOne of.The male sex chromosome is a pair ofX chromosomeAnd a smaller y chromosome.In organisms where the male is heterotypic and sexually determined,maleThe sex chromosome that the female does not have is called the Y chromosome.Because of the characteristic that the Y chromosome passes from male to female, it has left a genealogy of genes on the Y chromosome. Y-DNA analysis has now been applied to the study of family history, the inheritance and evolution of family lineages, and the identification of genes for recognizing ancestors.
For mammals, it containsSRY gene, can triggertestisThe occurrence of, therefore, determines the male character.The human Y chromosome contains about 60 millionBase pair。The genes on the Y chromosome can only be transferred from the male in the parents to the male in the offspring (i.efatherPass it on to his son), the Y chromosome in men has anti-cancer effect, and smoking will make men lose Y chromosome and increase the risk of cancer.
When people prove that a child's biological father is a man through DNA testing, scientists believe that the answer is yes, the Y chromosome can explain the origin of all human beings on the earth.However, in order to find a common ancestor, it is necessary to find the person who left their genetic imprint on many people, that is, the "super ancestor".They are like a branch point, countless branches, which will eventually be attributed to one person.Geneticists can trace down the tree gradually until they find the final root - Scientific Adam.
Basic meaning
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chromosomeIt is the carrier of genetic material, which exists in the nucleus of interphase cells.There are 23 pairs and 46 chromosomes in human, 22 of which are calledAutosomeBoth male and female autosomes are the same;The rest are calledSex chromosome, men and women are different. The male sex chromosome is composed of an X chromosome and a Y chromosome, namely XY, while the female sex chromosome is composed of two identical X chromosomes, namely XX.
stayspermIn the process of formation,germ cellAfter meiosis, the chromosomes in the nucleus includeAutosomeandSex chromosomeThey are all divided in two, so a sperm no longer contains 23 pairs of chromosomes, but only 23 chromosomes. At this time, half of the sperm has X sex chromosomes, called X sperm;The other half of spermatozoa have Y sex chromosomes, called Y spermatozoa.
As a male specific chromosome, the small and inconspicuous Y chromosome has long been ignored by geneticists.Human Genome ProjectThe precise location of all genes on the Y chromosome has been completed, and the in-depth understanding of the Y chromosome will help to findMale infertilityAnd other diseases.The Y chromosome can be used to study the family lineage because of its characteristic of passing from male to femaleHeredity and evolution。
MostMammalsEach cell has a pair ofSex chromosome。The male has one Y chromosome and one X chromosome;Females have two X chromosomes.Mammalian Y chromosome containsembryonic developmentThe gene that becomes male is calledSRY gene。Other genes located on the Y chromosome are normally manufacturedspermRequired[1]。
nature
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Y chromosome in Drosophila melanogaster
It is paired with the X chromosome during meiosis,X chromosomeAnd Y act like a pairHomologous chromosomeTherefore, it is considered that some of them are homologous, but most of them are different in morphology and structure.Of course, X chromosome and Y chromosome can exchange with each other in homologous part.The number of Y chromosomes may not be only one. Rumex (Y1Y2), for example, contains several Y chromosomes, but it is actually like one Y chromosome because it often acts together during meiotic separation.The mechanism of Y chromosome differentiation and its function are still unclear,Drosophila melanogasterThe middle Y chromosome is almost only composed of heterochromatin. Generally, there are only a few genes in the Y chromosome, which does not play a role in sex determination. It is believed that there are polygenic lines.
On the other hand, even if there is one Y chromosome and three X chromosomes in Melandrium of Caryophyllaceae, it also has a strong ability to determine the male.stayhempIn Cannabis, the X chromosome determines that the plant becomes female, and the Y chromosome determines that the plant develops into male.
In humans, the Y chromosome has a strong male determining gene. Even in individuals with multiple pairs of X chromosomes, as long as the Y chromosome exists, both internal and external sexual organs are male.The long arm end of the human Y chromosome is stained with quinoline nitrogen mustard, which can emit strong fluorescence.In the nucleus of the somatic cell during cell division, it can be observed that this part is a body that can emit fluorescence, so it is calledF corpuscle（Fluorescent corpuscleIt is a fiuorescent body), which can be used for gender identification.
10. Y chromosome isHomologous chromosomeThere are 23 pairs of chromosomes in human somatic cells, 22 of which areAutosome, 1 pair isSex chromosomeX and Y chromosomes.But the structure of X and Y chromosomes is different from that of autosomes;The segment on the X chromosome that cannot be found on the Y chromosome is the non homologous segment of the X chromosome;The segment on the Y chromosome that cannot be found on the X chromosome is the non homologous segment of the Y chromosome, that is, both X and Y chromosomes have their own homologous and non homologous segments.
Introduction to Sequencing
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Sequencing work
American scientists have completed the gene sequencing of the human Y chromosome and found that this sex chromosome, which has always been considered fragile, is more capable of self-protection than people think.
This achievement will help people improve their understanding ofMale infertilityTo understand, and to study better methods of diagnosis and treatment.It will also rekindle the debate about the evolution of gender.
There is a unique structure in the Y chromosome, which enables it to self repair harmful genetic variations to a certain extent.
The Y chromosome is the chromosome that determines the male sex. Unlike most paired chromosomes, the Y chromosome can only be paired with the X chromosome at its end during meiosis.Two paired chromosomes act as "backup" to each other, can exchange genetic material (recombination), eliminate harmful variation and protect genes.
It is generally believed that, due to the lack of such reserve, the non recombination region of the Y chromosome suffers much more damage in gene variation than other chromosomes, and is therefore in degradation, which is also the main theme in the evolution of the Y chromosome.
Chromosome structure
Chromosome structure
However, this gene sequencing found that the Y chromosome contains about 78 protein coding genes, more than the original thought of about 40.More importantly, there are some palindrome structures in the Y chromosome, which may play a role in gene repair.This may explain the mechanism of how males retain genes that are crucial to gender and survival in the process of Y chromosome disintegration.Chromosome presentationDouble helix structureIf the two base sequences on the chromosome double strand corresponding to one of the regions are essentially identical, this region is a palindrome structure.
Of the 50 million base pairs of the Y chromosome, about 6 million are in palindrome structure.The longest palindrome structure is 3 millionBase pair。Scientists said that the Y chromosome looks like a "hall full of mirrors" due to the existence of a large number of palindrome structures.This feature makes the sequencing of Y chromosome extremely laborious.
The study found that the Y chromosomePalindrome structureIt contains many genes. Since the two corresponding sequences in palindrome structure are actually the same, there are two copies of a gene in palindrome structure.In this way, although the Y chromosome has no paired chromosome to exchange genetic material, it can complete a "gene transformation" process internally, and carry out similar repair of gene variation.
Scientists say that the frequency of gene transformation in the Y chromosome is as high as that of gene exchange in general chromosomes.In only one generation of inheritance from father to son, there will be 600 base pairs rewritten on the Y chromosome.
However, this self-protection strategy of the Y chromosome is a double-edged sword. Although palindrome structure enables genes to be repaired, it is also this repetitive structure that makes genes more vulnerable to loss.Many genes in palindrome structure controlTesticular development, gene loss will lead to infertility.It is estimated that one in every thousand men is infertile for this reason.
In addition, for the Y chromosome, in addition to disintegration, it also acquired fertility genes in the process of evolution.The mechanism remains to be explored by scientists[2]。
Microdeletion
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Research
Chromosome deletion
The Y chromosome, which determines male sex, is the carrier of genetic material.There are 23 pairs (46 chromosomes) of human chromosomes, of which 22 pairs are euchromosomes, both male and female;The remaining pair isSex chromosomeThe female chromosome is composed of two identical chromosomes, written as XX, while the male chromosome is composed of one X chromosome and one Y chromosome, written as XY, and the Y chromosome is the chromosome that determines the male sex.
according toworld health organizationAccording to statistics, 10% of couples in the world suffer fromInfertility，Male infertilityAbout half of them, more than 30% of them are due toGenetic abnormalityCaused by.Y chromosome microdeletion is the main genetic factor leading to male infertility.
In 1976, Tieplolo and Zuffardi found that the long arm of Y chromosome (Yq11) was missing in patients with azoospermia, so this site was called azoospermia factor (AZF).At least three spermatogenic sites (AZFa, AZFb and AZFc) have been identified, which are located at the proximal, middle and distal ends of Yq11, respectively.
Y chromosome microdeletions occur in multiple genes related to AZF on the Y chromosome.Although the detection rate varies greatly due to the different selection criteria of test objects in each laboratory, the deletion frequency in each area is basically stable: Azfc accounts for 79% of the total deletion rate, Azfb accounts for 9%, Azfa+b accounts for 6%, Azfa accounts for 3%, and Azfa+b+c accounts for 3%.Microdeletion of these genes will lead to spermatogenesis disorders, oligospermia, asthenospermia, azoospermia and infertility.
Studies have shown that Y chromosome microdeletions are caused by gene recombination, which is related to a large number of high repetition and palindrome sequence characteristics on the y chromosome.Y chromosome microdeletions can be transferred from normal sperm with microdeletions.You can also use normal sperm to fertilizeembryonic developmentY chromosome microdeletion occurred in the process.In addition, modern assisted reproductive technology may also inherit the Y chromosome.
Normal father with missing sperm with missing son
Normal father - normal sperm - embryos with deletion/sons with deletion - infertile sons
Father with missing infertility - assisted reproduction - son with missing infertility - son with infertility
Inheritance and phenotype
There is a correlation between family name and Y chromosome type
The frequency of Azfa missing is the lowest, but the consequences are the most serious.In most cases, the whole Azfa deficiency occurs, showing severe oligozoospermia andSertoli cellSyndrome.Azfb and Azfb+c also showazoospermiaorOligospermia。
Whether the whole Azfa or Azfb is missing, or Azfb+c is missing, the chance of obtaining sperm by means of testicular biopsy is almost zero.Such patients are advised not to conduct puncture and ovulation induction on the female side.It can reduce unnecessary economic burden and various complications.
Azfc is missing most frequently, and the situation is relatively optimistic.The sperm count of the deletion patients went from none to normal, but usually accompanied by abnormal sperm morphology.The European Reproductive Association research shows that the effect of assisted reproduction with ISCI and other technologies for azoospermia patients caused by Azfc deficiency is generally good.However, the male offspring of these patients also suffer from Azfc deletion.
Inspection crowd
Who needs to check for Y chromosome microdeletions?
Distribution of human Y chromosome in the world
Azoospermia,AsthenospermiaPatients, patients with unknown diseases, and spouses with unknown causesHabitual abortionForty five percent of men need to be examined for Y chromosome deletion.Later studies found that for the largest proportion of Azfc deletion, the sperm count of patients could change from azoospermia to normal.Therefore, a normal number of sperm does not necessarily mean that there is no Y chromosome microdeletion.In addition, it was also found thatazoospermiaandOligospermiaPatients (testicular lesions, obstructive azoospermia,Varicocele）Patients with chromosomal changes (aneuploidy, deletion, translocation) andkaryotypeY chromosome microdeletions were also detected in normal patients with severe phenotypic abnormalities.
Whether the cause is unknown or clearMale infertilityY chromosome deletion detection is required for all patients, especially for intracytoplasmic sperm injection and other artificial assisted reproductive treatment.In developed countries in Europe and America, Y chromosome microdeletion has becomeMale infertilityRoutine inspection items of.If the male infertility patients have Y chromosome microdeletion, the general drug treatment is invalid.
useY chromosome microdeletion detectionThe product directly detects Y chromosome microdeletions at the gene level and molecular level for intracytoplasmic sperm injection and other artificial methodsAssisted reproductive technologyProvide a strong diagnostic basis.The treatment methods for different site deletions or whether there are deletions are different.The results of the test will guide doctors whether to use intracytoplasmic sperm injection technology to assist fertility;At the same time, it provides the basis for whether to selectively transfer female embryos and whether to selectively transfer female embryos, because male offspring will inherit the father's infertility defect.Testing is very convenient for patients as long as a small amount of blood is drawn.
Extended research
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1、 Research shows that human Y chromosome evolves faster than other Y chromosomes
The joint research team of Japan and South Korea found that,chimpanzeeThe difference of DNA base sequence between human Y chromosome and human Y chromosome is 1.78%, which is greater than the overall difference of genome base sequence, indicating that the evolution speed of human Y chromosome is faster than other Y chromosomes.Y chromosome is the chromosome that determines the male sex of mammals, and the genetic information on this chromosome is usually transmitted between father and son.
Y chromosome has self-healing function
The joint research team composed of the Comprehensive Research Center of Genome Science of the Japanese Institute of Physics and Chemistry and Korean scientists published an article on the online edition of the latest issue of Nature Genetics, saying that they had analyzedPrimate Institute of Kyoto UniversityThe Y chromosome base sequence of a male chimpanzee was found to be 1.78% different from that of human Y chromosome base sequence.
The American journal Science once published an article, which reported that scientists took 64000 DNA fragments from the chimpanzee gene map and constructed a physical map of the genome compared with that of chimpanzees.By comparison, scientists found that 98.77% of the base pair arrangement of the two were identical, so they thought that the DNA sequence difference between humans and chimpanzees was only 1.23%.
The researchers said that the difference between chimpanzee and human Y chromosome base sequence is greater than the overall difference of genome base sequence, indicating that the evolution of human Y chromosome is faster than other chromosomes.The researchers also found that the gene "CD24L4" does not exist in the Y chromosome of chimpanzees.This gene guides the synthesis of humanImmune cellSurface proteins.
Researchers believe that the human Y chromosome acquired the "CD24L4" gene about 5 million years ago after humans and chimpanzees began to independently evolve from a common ancestor to form a branch. This gene may explain the difference in immune function between humans and chimpanzees in dealing with infectious diseases.
A report in the weekly journal Nature said that the human Y chromosome is about 30% different from the chimpanzee Y chromosome, which is far higher than the 2% difference between other human genetic codes and chimpanzees.Massachusetts Institute of TechnologyDavid Page, a biology professor and one of the authors of the report, said: "The Y chromosome unique to men seems to be one of the fastest evolving chromosomes in human beings. It carries out gene recombination almost non-stop, just like a house is constantly being transformed."
2、 Y chromosome may help prevent testicular cancer from worsening
Previous studies have shown that if some substance produced by androgen binding with its receptor enters the nucleus of testicular cells too much, it will lead to abnormal cell proliferation and then deteriorate.The University of TokyoMolecular Cell BiologyInstitute professorKato MaomingIn their research, researchers found that the protein "TSPY" synthesized by genes on the male Y chromosome can prevent the substance produced by the combination of androgen and its receptor from entering the nucleus of testicular cells. However, in the cells of patients with testicular cancer, the production of "TSPY" protein continues to decrease.
The researchers also found that there was no difference at the gene level between the Y chromosome of patients with and without testicular cancer deterioration. They speculated that some problem occurred in the synthesis of "TSPY" protein, which led to the above results.
Testicular cancer The pathogenesis and deterioration mechanism of testicular cancer are poorly understood. In addition to the removal of testicles, there is no very effective treatment for testicular cancer.
The pathogenic gene of this kind of genetic disease is located in YchromosomeOn the X chromosome, there is no corresponding gene, so these genes can only be passed along with the Y chromosome, from father to son, from son to son, and so on.Therefore, it is called "all male inheritance".
(1) The pathogenic gene is only located on the Y chromosome, and there is no obvious or recessive difference. In the offspring of patients, all men are patients, all patients are men, all women are normal, and all normal ones are women.
(2) The pathogenic gene is passed from father to son, and from son to grandson. It has continuity of generations, also known as male restricted inheritance.
Common diseases include: human external auditory canalHirsutism, duck web disease, porcupine disease, etc.
4、 Y chromosome makes men live five years longer
A study that has been followed for many years shows that normal Y chromosome can make men live five years longer and reduce the risk of cancer.
The subjects were men in their 70s and early 80s. In the white blood cells of those who had cancer or died prematurely, the Y chromosome tended to be missing.When cells divide and mutate, the wrong replication process sometimes results in the loss of genes or even the whole chromosome.The researchers believe that these blood cells areimmune systemSome of them can usually help to find and destroy cancer cells. Without the Y chromosome and its genes, these cells will not be able to complete their respective missions.
A study that lasted more than 40 years was recently published in Nature Genetics. The study tracked about 1100 Swedish men all year round. The results showed that middle-aged and elderly men who had some mutations in their bodies and lost blood cells of Y chromosome would live about five years less than those who did not lose Y chromosome, including the high incidence of cancer.The research results show that the Y chromosome can also carry key genetic genes, which can protect the body from cancer and prolong the life span of men.
5、 Smoking causes men to lose their Y chromosome
The research reported on December 6, 2014 found that men who smoke are twice as likely to lose their Y chromosome as men who do not smoke, which may explain why men are more likely to suffer from and die from multiple cancers than women.
On December 4, 2014, Reuters published an article entitled "Scientists find the reason why smoking men face greater health risks",Uppsala University, SwedenA research report published by researchers in the US weekly Science said that compared with men who have never smoked or have quit smoking, the Y chromosome, which is crucial for determining gender and sperm production, often disappears from the blood cells of men who smoke.
Since only men have the Y chromosome, this finding may also explain why smoking is more likely to cause cancer in men than in women.
Those who participated in this studyUppsala UniversityProfessor Jan Dumanski said: "There is a certain relationship between the disappearance of the Y chromosome, the most common mutation in the human body, and smoking."
"This may partly explain why men tend to live shorter than women, and why smoking is more harmful to men," he said
The research team analyzed the data of more than 6000 men.The researchers found that the disappearance of the Y chromosome in smoking men seems to depend on the number of cigarettes smoked. In other words, the more cigarettes smoked, the more Y chromosomes lost. Some men who have quit smoking seem to regain the Y chromosome.
Lars Fosbury, who participated in the study, said that this showed that the process of Y chromosome loss caused by smoking could be reversed.
Scientists are still unable to determine whether the disappearance of Y chromosome in blood cells is related toSuffer from cancerWhat is the connection between them, but one possibility is thatImmune cellAfter losing the Y chromosome, the ability to fight cancer cells will decline.
6、 Without the Y chromosome, men will not disappear
Although the Y chromosome of human men is slowly losing genes, and the Y chromosome is 1/3 smaller than the X chromosome of women, the genes are much less, and even the functional genes involved in protein coding are less than 1/10 of the X chromosome, the core genes of the Y chromosome are still stable and powerful.It is the symbol of male, only exists in male body, and encodes genes that are very important for male reproduction.
More importantly, gene loss does not only play a negative role. There are too many duplicate genes and inert genes without any physiological function on the Y chromosome. It just keeps discarding useless genes in the process of evolution.However, in any case, the Y chromosome is too short and there are too few genes. It is quite easy to lose it, which has led some scientists to worry that there will be no baby boys in five million years.But without Y chromosome, will it be the country of daughter?The answer is no.
The research team led by Monika A. Ward, professor of the Institute of Biological Origin, John A. Burns School of Medicine, University of Hawaii, confirmed that only two key genes on the Y chromosome determine gender: Sry and Eif2s3y.The testicular determinant Sry is responsible for the development of the fetus into a male,SpermatogoniaThe proliferation factor Eif2s3y is related to spermatogenesis.This research team, in cooperation with researchers from France, has taken another step forward to produce male mice that completely lack the entire Y chromosome.
In this article published in Science（Science）In the new research in the journal, Ward and his colleagues described the process of building "Y chromosome free" male mice, and determined that these male mice can produce germ cells and have the ability to produce offspring.
The researchers first used its homologue, the direct target gene Sox9 encoded on chromosome 11, to replace the Y chromosome gene Sry.Under normal circumstances, Sry activates Sox9, which will start a series of molecular events, and eventually lead toembryonic developmentIt is male.Researchers usetransgenic technologySox9 is activated in the absence of Sry.
Next, they replaced the second necessary Y chromosome gene Eif2s3y with the homologue Eif2s3x encoded on the X chromosome.Eif2s3y and Eif2s3x belong to the same gene family and are very similar in sequence.The researchers speculate that these two genes may play a similar role, and the total dose of both genes is crucial.They overexpressed Eif2s3x through transgenic technology, and increased this X chromosome gene to a dose higher than that normally provided by X and Y chromosomes.Under such conditions, Eif2s3x took over the function of Eif2s3y and started spermatogenesis.
Finally, Ward's team replaced Sry and Eif2s3y at the same time, and constructed male mice without any Y chromosome DNA.Mice lacking all Y chromosome genes developedtestis, which is full of male germ cells.They collected round sperm cells and successfully fertilized oocytes using a technique called round sperm cell injection (ROSI).Will developembryo transferIn the body of the surrogate mother of male and female mice, live offspring of mice are generated.
The offspring of male mice without Y chromosome are healthy and have a normal life span. Their daughters and grandsons are fertile. Without further technical intervention, they are fertile themselves.Ward's research team used ROSI to generate three consecutive generations of Y chromosome free male mice, which proved that the male mice without Y chromosome genes can reproduce multiple times with the help of technology.
This study provides some important new insights on the function and evolution of Y chromosome genes, which supports the view that there is functional redundancy between Y chromosome genes and homologous genes encoded on other chromosomes.Ward said: "This is good news, because it shows that there are some backup strategies in the genome. These strategies of silence under normal circumstances can take over the corresponding functions under certain circumstances. We have revealed two such strategies through genome manipulation. It is not known whether such alternative signaling pathways can be activated in response to environmental changes without human help.But this is certainly possible, and has already occurred in two rodent species that lack the Y chromosome. "
The Y chromosome gene of Japanese echinococcus and mole has been transferred to other chromosomes, so men need not worry about whether there will be siblings after millions of years. The Y chromosome is not so irreplaceable, especially in determining gender[2]。
7、 Related research
On August 23, 2023, the National Institute of Human Genome announced that all genes of human Y chromosome deoxyribonucleic acid (DNA) had been sequenced.Y chromosome is a sex determining chromosome, and the genetic information on this chromosome is usually transmitted only between males.This research result may contribute to the research on male infertility.[3-4]
Origin and evolution
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Many belong toAllothermOfvertebrateNoSex chromosomeOf.Their gender is determined by external environmental factors rather than individualsgenotypedecision.The sex of some of these animals (e.g. reptiles) may depend on the temperature at the time of incubation;OthersHermaphrodite(that is, they can produce both male and female gametes in each individual).
The ancestor of an ancient mammalAlleleVariation of“Sex locus”）- An individual with this allele will become a male.The chromosome containing one of the alleles eventually forms the Y chromosome, while the chromosome containing the other half of the allele eventually forms the X chromosome.With the passage of time and the selection of species by the environment, genes that are beneficial to male individuals but harmful to female individuals (or have no obvious effect) continue to be inherited and developed on the Y chromosome, and the Y chromosome also continues to passChromosome translocationGet these genes.
The X and Y chromosomes were once thought to have evolved in different directions for about 300 million years.However, recent research (especially the platypusGenome sequencing）It shows that the XY sex determination system only appeared about 166 million years agoMonotreme（Protozoa）From other mammals（Fauna）It started from the separation of.This time, the XY sex determination system of mammals in the subclass Zodiac was bornRenamingIs based onMarsupial（Fauna）AndPlacental animal（Zodiac）Some of the X chromosomes ofGene sequenceIt also appears in platypuses and birdsAutosomeHowever, earlier estimates were based on the fact that the platypus X chromosome contains some gene sequences of placental animals.
Between X and Y chromosomesGene recombinationIt has been proved thatLife formHarmful, it will cause male animals to lose the Y chromosome contained before recombinationEssential geneFemale animals have more unnecessary genes or even harmful genes that would only appear on the Y chromosome.Therefore, in the process of evolution, genes favorable to males gradually gathered near the sex determining genes, and then genes in this region developedRecombination inhibition mechanismTo protect this male specific area.The Y chromosome evolves along this route, inhibiting the recombination of genes on Y chromosome and X chromosome.This process ultimately prevents about 95% of the genes on the Y chromosome from recombination.
Homologous chromosomeThe gene recombinant version of is used to reduce the probability of harmful mutation retention and maintain genetic integrity, but the Y chromosome cannot be recombined with the X chromosome.The human Y chromosome lost 1393 of its 1438 genes during its evolution, about 4.6 genes lost every one million years.It is estimated that if the Y chromosome still loses genes at this rate, it may lose its function completely in 10 million years.The data of comparative gene analysis shows that many mammals are losing their ownHeterozygous chromosomeFunction of.However, some studies have pointed out that degradation may only occur in the non recombinableSex chromosomeUpper: Highmutation rate, inefficientnatural selectionas well asGenetic drift。On the other hand, an item on human andchimpanzeeThe comparison of Y chromosome shows that the human Y chromosome did not lose any genes before it was separated from apes six or seven million years ago and began to evolve alone, which may prove thatLinear extrapolationThe model is direct evidence of error.
In addition, these structures enable the Y chromosome to carry outSelf gene recombinationAnd other processes (these processes are called“Y-Y gene transformation”）This gene recombination is believed to maintain its stability.
Human Y chromosomes are particularly exposed to high rates of variation due to living conditions.The Y chromosome receives multiple cell divisions in gametes through sperm.Each cell division provides a further opportunity to accumulate base mutations.In addition, spermatozoa are stored in a highly oxidative and prosperous testicular environment, which makes them mutate further.The combination of these two conditions makes the mutation rate of Y chromosome 4.8 times higher than that of other genomes.
origin
A scientific research released on April 23, 2014 showed that the Y chromosome, the "sex gene" that determines human gender, was first produced about 180 million years ago.
Y chromosome is male and femalesex differenceThe key to.Y chromosome only exists in men, and its combination with X chromosome can express the physiological and morphological characteristics of men.In women, there is no Y chromosome and a pair of X chromosomes are paired to express female characteristics.
However, this is not always the case. The Y chromosome and the X chromosome were once the same, and evolved in different directions after a long time.The Swiss Institute of Bioinformatics and Australian scholars jointly found that about 180 million years ago, the "sex gene" first appeared in mammals.This research has been published in Nature.
The researchers extracted testis tissue samples from 15 kinds of mammals in 3 categories and compared them with the analysis results of chickens.It is worth mentioning that this study used computers to carry out a total of 29500 hours of calculation, and drew the largest "male" chromosome map.
The study found that SRY and AMHY, two "sex genes", appeared in different kinds of animals 180 million years ago and 175 million years ago, respectively, resulting in gender differentiation.The scholar Henrik Kosman said that both of them "are biologicaltestisThe evolution of is closely related, appearing almost simultaneously, but completely independent of each other. "
evolution
Several congenericMuridaeandHamster familyOfRodentThe Y chromosome evolution terminal has been reached through the following ways:
Ellobius lutescens （Ellobius lutescens）、Ellobius tancrei （Ellobius tancrei）AndJapanese prickly mouseInTokudaia osimensis （Tokudaia osimensis）AndTokudaia muenninki （Tokudaia muenninki）, has completely lost their Y chromosome (including SRY gene).Tokudaia （Tokudaia）Some mice under the group transferred the remaining genes originally on the Y chromosome to the X chromosome.The genotype of both male and female in the mole voles and the rodents of the genus Rattus is XO, and allEllobius tancrei The genotypes of both were XX.The sex determination system of these rodents has not yet been fully understood.
Lemming（Myopus schisticolor）、Dicrostonyx torquatus （Dicrostonyx torquatus）, andProtomus（Akodon）Through complex changes in the X chromosome and Y chromosome, many species in thefemale。
In femalesDiving vole（Microtus oregoni）Each individual cell has only one X chromosome and only one X gamete;However, the male diver is still XY, but it can passNon separation phenomenon(Nondisjunction) produces Y gametes and gametes without any sex chromosomes.
Except rodents,Black muntjac（Muntiacus crinifrons）By integrating the originalSex chromosomeandAutosomeNew X and Y chromosomes have evolved.PrimatesThe phenomenon that the Y chromosome of animals (including humans) has been seriously degraded indicates that this kind of animals will develop a new sex determination system relatively quickly.Scholars estimate that humans will acquire a new gender determination system in about 14 million years[2]。
