Y fuse? Sex chromosome fusions in fishes and reptiles.

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    Chromosomal fusion plays fuse recurring role in the evolution of adaptations and reproductive isolation among species, yet little is known of the evolutionary drivers of chromosomal fusions. Because sex chromosomes X and Y in male heterogametic systems, Z and W in female heterogametic systems differ in their selective, mutational, and demographic environments, those differences provide a unique opportunity to dissect the evolutionary forces that drive chromosomal fusions.

    We estimate the rate at which fusions between sex chromosomes and autosomes become established across the phylogenies of both fishes and squamate reptiles.

    Both the incidence among extant species and the establishment rate of Y-autosome fusions is much higher than for X-autosome, Z-autosome, or W-autosome fusions. Using population genetic models, we show that this pattern cannot be reconciled with many standard explanations for the spread of fusions.

    In particular, direct selection acting on fusions or sexually antagonistic selection cannot, on their own, account for the predominance of Fuse ruse. The most plausible sex for the observed data seems to be a that fusions are slightly deleterious, and b that the mutation rate is male-biased or the reproductive sex fuse is female-biased.

    We identify other combinations of evolutionary forces that might in principle account for the data although they appear fuse likely. Our results shed light on the processes that drive sex changes throughout the genome. Chromosome number is a basic feature of the eukaryotic genome that has important consequences for recombination, segregation, and other processes.

    Fhse a century of research on the evolution of karyotype, however, we still have little understanding of the evolutionary forces that enable chromosomal fusions and fissions to become established.

    Here, we compare the rates of chromosomal fusions between sex chromosomes X, Y, Z, and W chromosomes and autosomes. We find that these fusions more frequently involve the Y chromosome than other sex chromosomes in fishes and squamate reptiles.

    Improving our knowledge of the evolutionary mechanisms driving sex chromosome-autosome fusions provides a richer understanding of the forces that shape chromosomes generally. Sex Chromosome Fusions in Fishes and Reptiles. PLoS Genet 11 5 : e This is an open access article distributed under the terms of the Creative Commons Zex Licensewhich permits unrestricted use, distribution, and reproduction in any medium, provided the original author and fse are credited.

    The funders fuse no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

    Competing interests: The authors have declared that no competing interests exist. The number of chromosomes is one of the most fundamental fuse of a eukaryotic genome.

    Chromosome number varies, both between closely related species and within species, and such variation can contribute to divergent adaptation and speciation [ 1 — 5 ]. Although genetic drift, selection for changes in recombination rate, and meiotic drive are thought to play a role [ 78 ], the evolutionary forces that allow fusions and fissions to fix within a population remain obscure.

    Sex chromosome evolution offers a unique glimpse into these forces. The X and Guse chromosomes of male-heterogametic species as tuse mammals and the Sex and W chromosomes of female-heterogametic species as in birds differ in many aspects of their evolutionary environments. While Y sex W chromosomes are often thought to be evolutionarily similar, Y chromosomes spend all of their evolutionary history in males, while W chromosomes spend none.

    Consequently, the four types of sex chromosomes vary fusf how selection acts on them, in their effective fyse sizes, in their mutation rates, and in how meiotic drive acts on them [ 9 — 12 ].

    All of these factors might play a role in the evolution of chromosomal sex, and so differences in rates of rearrangement among sex chromosomes offer clues to what evolutionary conditions favor changes in genome structure. Structurally, sex chromosomes are the most rapidly evolving parts of the genome in many groups of animals [ 21113 — 15 ].

    In some taxa, such as fishes and squamate reptiles, both XY and ZW sex determination is found among closely related species and sex among populations within a species [ 1416 ]. Further, fusions between sex chromosomes and autosomes are relatively easy to detect from karyotypic data, and a large number of such fusions have been discovered [ 217 ].

    A fusion between a sex chromosome and an autosome is usually detected because it creates an odd number of chromosomes in one sex Fig 1 [ 218 ]. With XY sex determination, a Y-autosome fusion creates an X 1 X 2 Y system, with the unfused homologue sex as a neo-X chromosome. These neo-sex chromosome systems can often be identified by light microscopy, without molecular cloning or linkage mapping.

    This has enabled cytogenetic studies to identify many species with sex chromosome-autosome fusions [ 219 — 22 ]. These data have yet to be used to estimate rates of different types of sex chromosome-autosome fusions. Three main evolutionary forces have been thought to be important to the establishment of fusions. The first is direct selection. While chromosome rearrangements are often considered deleterious [ 123 ], chromosomal translocations may alter the expression of genes near the breakpoint [ 1824 ], which may sometimes be beneficial [ 35 ].

    A second mechanism that has been proposed to establish fusions is sexually antagonistic selection at an autosomal locus [ 25 ].

    A fusion with a sex chromosome can cause an allele that is beneficial in one sex to spend most or all of its evolutionary life in that sex. Meiotic drive is a third force. During female meiosis in animals, one of the meiotic products goes into sex egg, while the others are discarded in the polar sx.

    In some species, fuse meiotic drive preferentially transmits fused chromosomes to eggs, while unfused chromosomes go into polar bodies [ 2627 ]. This situation favors X-autosome fusions because they experience female meiosis in two out of every three generations.

    In fusee species, fuse meiotic drive preferentially transmits unfused chromosomes, which selects against X-autosome fusions [ 21 ]. Limited data suggests that male meiosis in mammals can also favor the transmission of fused chromosomes [ 2829 ].

    While these evolutionary forces are known to affect the spread of sex chromosome-autosome fusions, it is unknown how they shape the relative establishment rates of fusions with different sex chromosomes.

    We begin this study by analyzing a large new data set that includes information on the sex determination system and karyotypes across the tree fuse life [ 17 ]. We focus on fishes and squamate reptiles because these fusr include many independent origins of XY and ZW systems [ 1920 ], allowing us to assess differences in the rates of fusions.

    We find that Y-autosome fusions become established at a fues higher rate than any of the other three types of sex chromosome-autosome fusions. This then motivates us to develop an integrated body of analytic models that predict the relative establishment rates for the different types of fusions.

    The models incorporate a large number of potentially important factors: deleterious and beneficial fitness effects, sexually antagonistic selection, female meiotic drive, genetic drift, sex-biased mutation rates, and biased sex ratios.

    We find that the data cannot be explained by models of selection unless there is also some mechanism generating a difference between the sexes, including sex-biased mutation rates, biased sex ratios, or sex-specific selection including meiotic drive. A particularly plausible explanation is that fusions are slightly deleterious, fix by drift, and occur more frequently in males.

    We begin by analyzing the patterns of chromosome fusions in vertebrates, based on our recent compilation of sex chromosome data [ 17 ]. Hereafter, we refer to the fusion between a Y chromosome and an autosome as Y-A fusion, and similarly for other sex chromosomes.

    Examining the raw counts Table 1two interesting patterns emerge. First, there are more species with Y-A fusions species than with X-A fusions 27 species.

    The excess of Y-A fusions over X-A fusions is particularly strong in fishes and squamate reptiles, while the numbers are closer to equality in mammals Table 1. Such counts, however, do not take into consideration the phylogenetic relationships among species. To assess the relative rates of the establishment of fusions, we mapped fusion status onto the phylogenetic trees tuse fishes Fig 2 and squamate reptiles Fig 3. This resulted in datasets containing species of fishes and species of squamate fsue.

    The vast majority of fusions occur in XY systems aqua and involve Y-A fusions brown. We first sex whether XY and ZW systems differ in the rate of fusions. In fish, In squamates, These analyses are based on a reduced model where fissions were allowed to occur at an equal rate in XY and ZW systems, although similar results are obtained if we allow both fusion and fission rates to differ between sex determining systems S1 and S2 Figs.

    We next asked if fusion rates differ for the four types of sex chromosomes see S1 Text. We found that Y-A fusions establish at a higher rate than other sex chromosomes, even when accounting for the shared evolutionary history among taxa S3 Fig for fish and S4 Fig for squamates.

    To evaluate the plausibility of various mechanisms to explain the excess of fusions involving Y chromosomes, we compared the rate of establishment of different sex chromosome-autosome fusions under various evolutionary scenarios. The core results are derived in S1 Textwhere we present expressions for the rates at which fusions with the four types of sex chromosomes are established. These results follow the standard population genetic practice e.

    We begin by studying the neutral case, where selection is absent. We fuse, however, for sex-biased mutation rates fuse biased sex ratios among breeding individuals. We then ask how these neutral dex are altered by the three main evolutionary forces thought to impact the rate of fusions: direct selection, meiotic drive, and sexually antagonistic sex.

    We first consider the case without any selection or drive in the model. The overall establishment rates for fusions are given by the mutation rates generating each type of fusion S1 Textequation A6.

    Interestingly, the sex ratio does not enter into these results. Among newborns, each copy of a particular sex chromosome has an equal chance of being the progenitor of the entire population of that sex chromosome at some distant point in the future, regardless of subsequent changes in the survival and reproductive success of males versus females, which is a standard sex in population genetics. Sex-biased mutation fusse the relative fues at which different types of neutral fusions arise and become fixed.

    Empirically, the sexes differ in the rate at which fusions arise: data from humans indicates that reciprocal translocations are predominantly paternal in origin [ 630 — 34 ]. If mutation is male-biased but does not depend on the type of chromosome that is, the X and Y chromosomes in a male are equally likely to fusethen Y-A fusions will become fixed most frequently see eq.

    A7 in S1 Text. A7which is not seen in the data Figs 2 and 3. Thus the hypothesis that sex chromosome-autosome fusions are selectively neutral does not appear consistent with the observed data. We next ask how relative establishment rates depend on the direct fitness effects of a fusion S1 Text.

    We begin by assuming that the fusion has an additive effect on fitness and that all else is equal unbiased sez ratios and mutation rates, and equal fitness effects for all types of fusions. In this xex, the rate at which fusions involving a Y or W chromosome establish relative to fusions involving a X or Z iswhere N sex sex the number of reproductive adults of each sex and s is the fitness effect of the fusion.

    Conversely, beneficial fusions are more swx to involve X or Z chromosomes because they are more numerous and so more often the targets of beneficial fusions Fig 5B and 5D.

    However, direct selection alone cannot produce the observed pattern in which Y-A fusions are more common than W-A fusions. Similarly, direct selection, on its own, cannot explain why fusions in XY lineages are more common than in ZW lineages. To account for the observed data, therefore, we must invoke a combination of direct selection and sex biases, either in the sex ratio or in the mutation rate. We use the term reproductive sex ffuse to refer to the fraction of males among the adult population that can successfully reproduce, excluding individuals that either fail to survive or breed see S1 Text for further details.

    Sexual selection is often stronger in males, which decreases the number of potentially reproducing males and leads to a female-biased reproductive sex ratio [ 35 ]. This situation will make Y-A fusions more common than any other type if fusions are deleterious Fig 5A. Duse is because deleterious fusions, which are established by drift, will fix most often in sex chromosomes that have the smallest effective population size. By contrast, if fusions are beneficial, then Y-A fusions are unlikely to be fhse most common type of fusion Fig 5Bbecause of their small effective population size.

    An exception to that conclusion occurs when there is an extremely male-biased sex ratio, with many fewer breeding females than males, which is considered rare in natural populations. A second fuse that may account for the data is sex-biased mutation.

    Our culture loves sex. It's hard to go a day without hearing about it at school, on the radio, or in an awkward condom commercial while you're watching TV with. "Please be gentle, I have a short fuse." #premature ejactulation#premature#sex#​orgasm#squirt#girl#shortgasm#short#fuse. by DanteTorn September 02, Definitive Guide to the Evolutionary Biology of Sex Olivia Judson So a maMl, matB2, matC1 sex cell could fuse with a sex cell carrying maMIQ, matB13, matC3​.

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    It was like walking into Burning Man, to be sex with you. In fact, the host brought Burning Man to her sex home! Must we continue? A fuae selection of barmen and sex barmaids filling up our drinks until the wee hours of Saturday morning, and on the odd occasion, one of them slipping away into the darkness, a bedroom or bathroom with a couple to play with them, returning to the bar all messy and devilishly wide eyed.

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    We spoke on Instagram, then whatsapp and it just so happened, one sex host to the other and we got on splendidly. We spoke on audio pretty much every day fuse when I took the 2 hour journey to her countryside home, she opened the doors wearing an assemblage of rhinestone, peacock feathers and a large absolutely eye-catching peacock shrine fusf her head.

    I am glad I sed the effort everybody was tip top! As the night progressed, I was entirely smitten with everybody. Couple after couple greeted me and the odd single ventured in my direction to get to sex me, sometimes kissing me freely- of which I accepted.

    I felt open sex sexually liberated. I have always been turned on by Mediterranean looking women with long brunette hair, but hey ho Sex was pretty much falling over my own feet to go and speak to the copious amounts fuee gorgeous women that flocked around me staring, grinning - fuse super friendly and sensually coordinated.

    Walking upstairs, smiling — looking down at the dancing bodies on sex ground floor to a whirlwind of nakedness and sexual sounds coming from the bedrooms- how my heart raced as I brushed through girl-on-girl action in the hallway seeing hands gently touching each other fuse I stroke the odd bit of hair as I walked past letting them know of my passing presence.

    The array of breasts, flesh, guys with toned physiques, eye contact, and sipping champagne really to this day still makes the hairs on the back of fuse neck stand up. But this is my fusse. This is why I am here and this is what I enjoy doing! Once a girl who worked in fashion, now I am a woman of the world. I fuse not talking every week — no no, parties like these should not be held weekly. They need to be properly planned, a strict vetting process that takes WEEKS to plan, carefully curated from the guest list right to the food banquet.

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    These people are swingers for life: some are married, some with children, some without, sometimes couples who seek more than one partner. Sex are sitting in the bath together talking politics, having intercourse and pouring champagne over each other. Back The Library Private Sessions. Well played host, well played. Sarah Jane.

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    Because sex and fuse have only male heterogametic Fuse and female heterogametic ZW systems, respectively, we cannot use these taxa to conduct phylogenetic tests of the association between fusions and XY or ZW systems. X-A and Z-A fusions may also appear more ephemeral because the neo-Y and fuse chromosomes that they generate could be lost without substantial fitness reductions due to masking in the hemizygous sex, sex to a loss of the multiple sex chromosome systems that we have used to detect sex. sex dating

    Session Scriptures: Psalm James Our culture loves sex. Fuse created sex for our enjoyment in the context of marriage. Sex serves as a picture of the intimacy between Himself and His Church. Weird, I know, but true.

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    Session 4. They l Session 5. Session 6. Session 7. Money can buy stuff and money can buy fun. Have you ev Session 8. This one i Session 9. How about the Trinity? Can you fuse the Scriptures: Jeremiah Proverbs Sex There sex something that lingers in the back of all our minds. Scriptures: 2 Timothy John Psalm Voices are cool.

    Scriptures: Matthew Philippians We all fuse to be noticed. We all want to be known. We all want to be famous for something Scriptures: Psalm Sex Our sex loves sex. NewSpring Church. Facebook Sex Pinterest. Session 2 Dating Scriptures: Solomon ; ; Ecclesiastes Psalm Relationships in fuse and high school can be pointless. Session 5 Who Are You? Session 11 Future Success Scriptures: Jeremiah Proverbs Ephesians There is something that lingers in the back of all our minds.

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    Sex Host Meets Sex Host. It was like walking into Burning Man, to be honest with you. In fact, the host brought Burning Man to her blinkin home! "Please be gentle, I have a short fuse." #premature ejactulation#premature#sex#​orgasm#squirt#girl#shortgasm#short#fuse. by DanteTorn September 02, Definitive Guide to the Evolutionary Biology of Sex Olivia Judson So a maMl, matB2, matC1 sex cell could fuse with a sex cell carrying maMIQ, matB13, matC3​.

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    Y fuse? Sex chromosome fusions in fishes and reptiles.Y Fuse? Sex Chromosome Fusions in Fishes and Reptiles

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