- recombination
- We are now exploring this remarkable neo-sex chromosome system to understand the evolution of sex chromosomes in terms of recombination cessation and gene content. (lu.se)
- To understand sex chromosome evolution in terms of recombination cessation, degeneration and gene content. (lu.se)
- If one of the sex chromosomes carries a sex-determining region with at least two loci that should be linked together, selection favours the process of preventing sex chromosomes from recombination [ 1 , 2 ]. (royalsocietypublishing.org)
- In turn, the lack of recombination leads to degeneration of the chromosome that is present only in one sex. (royalsocietypublishing.org)
- Recombination, which is the process of swapping bits of genetic material between a pair of chromosomes during the formation of eggs or sperm, is essential to maintaining genetic identity between X and Y. Without it, the two chromosomes would diverge into completely distinct forms. (abc.net.au)
- Page and Lahn say differentiation between the two chromosomes could have occurred only after recombination between the X-Y genes was suppressed. (abc.net.au)
- The crucial events, including meiotic chromosome pairing and recombination, take place from around 11 weeks until birth. (warwick.ac.uk)
- Unlike the autosomes, recombination between the X chromosome and Y chromosome is often thought to be constrained to two small pseudoautosomal regions (PARs) at the tips of each sex chromosome. (genetics.org)
- Genetic diversity is expected to be higher in recombining regions than in non-recombining regions because recombination reduces the effect of linked selection. (genetics.org)
- However, rather than an abrupt drop in diversity at the pseudoautosomal boundary, there is a gradual reduction in diversity from the recombining through the non-recombining region, suggesting that recombination between the human sex chromosomes spans across the currently defined pseudoautosomal boundary. (genetics.org)
- A consequence of recombination spanning this boundary potentially includes increasing the rate of sex-linked disorders (e.g., de la Chapelle) and sex chromosome aneuploidies. (genetics.org)
- autosomes
- Sex chromosomes have evolved from non-sex-determining chromosomes (autosomes) many times throughout the tree of life. (lu.se)
- The initial steps in XCI involve a 'counting process', which senses the X chromosomes/autosomes ratio and restricts XCI to female mouse embryos. (embopress.org)
- segregation
- We propose a model in which ObgE is required to license chromosome segregation and subsequent cell cycle events. (wiley.com)
- The speed at which this occurs (reviewed in Gordon and Wright, 2000 ) rules out passive models for bacterial chromosome segregation, which proposed that outward cellular growth could drive the movement of a fixed chromosome. (wiley.com)
- Therefore, segregation of oriC , ter and the rest of the chromosome could have unique determinants. (wiley.com)
- Progressive condensation of the chromosome as it emerges from the replisome may provide force or organization of the chromosome to facilitate segregation. (wiley.com)
- Defects in chromosome segregation play a critical role in producing genomic instability and aneuploidy, which are associated with congenital diseases and carcinogenesis. (biologists.org)
- Here we investigate whether human primary fibroblasts exhibit similar errors in chromosome segregation and if at least part of lagging chromosomes may arise in cells entering anaphase in the presence of mono-oriented chromosomes. (biologists.org)
- Thus, our results demonstrate that the mitotic checkpoint efficiently prevents the possible aneuploid burden due to mono-oriented chromosomes and that merotelic kinetochore orientation is a major limitation for accurate chromosome segregation and a potentially important mechanism of aneuploidy in human cells. (biologists.org)
- It is generally accepted that most aneuploid fetal conditions, such as trisomy 21 Down syndrome, are due to maternal chromosome segregation errors. (warwick.ac.uk)
- It is also clear that superimposed on the maternal meiotic chromosome segregation errors, there are a large number of mitotic errors taking place post-zygotically during the first few cell divisions in the embryo. (warwick.ac.uk)
- In this chapter, we summarise current knowledge of errors in chromosome segregation during oogenesis and early embryogenesis, with special reference to the clinical implications for successful assisted reproduction. (warwick.ac.uk)
- accumulate
- Finally, we use our unique 30-year ecological dataset and rich collection of DNA samples of the great reed warbler to test the widely accepted but poorly supported sexual antagonism hypothesis suggesting that sexually antagonistic mutations accumulate on the sex chromosomes and drive their evolution. (lu.se)
- To understand the interplay between sex chromosomes and sexual conflicts by studying whether sexually antagonistic mutations accumulate on sex chromosomes, and whether sexual conflicts drive sex chromosome evolution. (lu.se)
- Escherichia coli cells depleted of the conserved GTPase, ObgE, show early chromosome-partitioning defects and accumulate replicated chromosomes in which the terminus regions are colocalized. (wiley.com)
- autosome
- Our research focuses mainly on Sylvioidea passerine birds where we have recently detected a new sex chromosome, a neo-sex chromosome, which has been formed by a fusion between an autosome and the ancestral sex chromosomes. (lu.se)
- A counting process senses the X chromosome/autosome ratio and ensures that X chromosome inactivation (XCI) initiates in the female (XX) but not in the male (XY) mouse embryo. (embopress.org)
- investigate
- This is an ideal situation for research on sex chromosomes, because the processes we wish to study have had some time to leave detectable genomic footprints, but have not yet removed the material we want to investigate. (lu.se)
- Further studies are now needed to investigate how chromosome morphology relates to its gene content, and whether the changes in size were driven by selection. (royalsocietypublishing.org)
- In this study, we investigate patterns of genetic diversity in noncoding regions across the entire X chromosome of a global sample of 26 unrelated genetic females. (genetics.org)
- abnormalities
- An increasing number of studies have shown that abnormalities such as aneuploidy and whole-chromosome loss of heterozygosity are commonly present in tumor cells. (biologists.org)
- mutations
- However, in a ZW system one can separate the effect of the hemizygous chromosome from the male-biased mutations, providing an excellent system for understanding the evolution of SCD. (royalsocietypublishing.org)
- They then compared the number of mutations between the X form and the Y form of a pair of X-Y genes to come up with rough estimates of when they were last alike, giving them a 'geologic' snapshot of sex chromosomes. (abc.net.au)
- evolutionary
- We found no support for the view that W chromosomes gradually become smaller over evolutionary time. (royalsocietypublishing.org)
- Parallel to what is observed in Y, the W chromosome in birds and snakes also seems to have degenerated over evolutionary time scales. (royalsocietypublishing.org)
- Researchers at the Howard Hughes Medical Institute have found that the X and Y chromosomes evolved from a standard identical pair around 300 million years ago - shortly after the divergence of the evolutionary lines leading to mammals and birds. (abc.net.au)
- 19 genes shared between the X and Y served as the "fossils" that helped Lahn and Page to reconstruct the evolutionary history of sex chromosomes. (abc.net.au)
- birds
- Recent discoveries of near-identical palindromes and neo-sex chromosomes in birds may also contribute to the observed variation. (royalsocietypublishing.org)
- mechanism
- The mechanism by which specific regions of the chromosome are organized and segregated prior to division remains a mystery. (wiley.com)
- We recently provided evidence from immunofluorescence and electron microscopy studies that merotelic kinetochore orientation is a major mechanism for lagging chromosomes during mitosis in PtK1 cells. (biologists.org)
- The selected Xi becomes the target of a chromosome‐wide mechanism of transcriptional silencing, which constitutes an exciting paradigm for epigenetic regulations and confirms interest in the molecular dissection of the X‐inactivation centre ( Xic ), a locus on the X chromosome that contains the Xist gene and the elements involved in counting, choice and silencing. (embopress.org)
- mitotic
- By using in situ hybridization with alphoid probes to chromosome 7 and 11 we showed that loss of a single sister is much more frequent than loss of both sisters from the same chromosome in anatelophases from human primary fibroblasts released from a nocodazole-induced mitotic arrest, as predicted from merotelic orientation of single kinetochores. (biologists.org)
- Kinetochores of lagging chromosomes in anaphase human cells were found to be devoid of the mitotic checkpoint phosphoepitopes recognized by the 3F3/2 antibody, suggesting that they attached kinetochore microtubules prior to anaphase onset. (biologists.org)
- Mitotic chromosome malsegregation produces aneuploidy and genome instability. (biologists.org)
- Hence, the activation of the mitotic checkpoint prevents the unbalanced distribution of chromosomes during mitosis and the production of aneuploid cells. (biologists.org)
- occurs
- Live cell imaging of H2B histone-GFP-transfected cells showed that cells with mono-oriented chromosomes never enter anaphase and that lagging chromosomes appear during anaphase after chromosome alignment occurs during metaphase. (biologists.org)
- X chromosome inactivation (XCI), which occurs only in female (XX) and not in male (XY) embryos, ensures dosage compensation of X‐linked genes between the sexes. (embopress.org)
- degeneration
- This neo-sex chromosome is evolutionarily very interesting and promising for research: First, the female-specific neo-W chromosome is in an intermediate stage of degeneration. (lu.se)
- The well-established view of the evolution of sex chromosome dimorphism is of a gradual genetic and morphological degeneration of the hemizygous chromosome. (royalsocietypublishing.org)
- Genetic degeneration, accompanied by morphological shrinking of hemizygous chromosomes, is observed in both XY and ZW chromosome systems [ 2 , 4 ]. (royalsocietypublishing.org)
- researchers
- Ever since their discovery, these chromosomes have captivated researchers because of their obvious involvement in fundamental aspects of an organism's life, such as sex determination, sexual reproduction and sexual conflicts. (lu.se)
- First the researchers compared the locations of the 19 fossil gene pairs on the human X and Y chromosomes. (abc.net.au)
- human
- The idea of morphological reduction of W is also enhanced by our perspective of the gradual shortening of human Y chromosome [ 5 ], although there are examples of Y becoming larger than X in non-human species [ 2 ]. (royalsocietypublishing.org)
- Of our 46 human chromosomes, 44 form matched pairs. (abc.net.au)
- Nevertheless, many genes on the human Y chromosome have homologues (analogous genes) on the X chromosome. (abc.net.au)
- The reconstruction of the defining events of human sex-chromosome evolution is analogous to the reconstruction of the evolution of species, except that we are looking at changes of a pair of chromosomes over geologic time rather than changes of whole organisms," says Lahn. (abc.net.au)
- New insights into human nondisjunction of chromosome 21 in oocytes. (warwick.ac.uk)
- The PAR1 spans the first 2.7 Mb of the proximal arm of the human sex chromosomes, while the much smaller PAR2 encompasses the distal 320 kb of the long arm of each sex chromosome. (genetics.org)
- boundary
- Second, the neo-sex chromosome is homologous to the sex chromosomes of mammals, which makes it possible - for the first time - to study mammalian X gene homologs in a novel, avian Z-linked environment where females are the heterogametic sex (ZW), and thus to draw direct parallels over the avian ZW-mammalian XY boundary. (lu.se)
- distinct
- Meiotic chromosome development during oogenesis is subdivided into three distinct phases. (warwick.ac.uk)
- found
- The X chromosome was found to have four groups of genes physically arranged as four consecutive blocks, like the layers of rock in geological strata. (abc.net.au)
- process
- The speed at which chromosomes segregate appears to require an active process, but the machinery remains elusive. (wiley.com)
- events
- The first events that created the sex chromosomes had been thought to have occurred at least 170 million years ago," says researcher Dr David Page. (abc.net.au)
- By fossil digging on the sex chromosomes, we were able to reconstruct the four events that drove sex chromosomes into their distinctive X and Y forms, and to date when these events occurred during evolution," says Lahn. (abc.net.au)
- evolution
- This lack of detailed knowledge about sex chromosome evolution compromises our understanding of fundamental biological questions (e.g. the evolution of sexual conflicts) as well as more practical ones (e.g. about sex-linked genetic diseases). (lu.se)
- The evolution of sex chromosome dimorphism (SCD) is generally thought to follow a repeatable pattern. (royalsocietypublishing.org)
- Alternatively, it is plausible that during the course of evolution the genetic degradation of W was not always accompanied by its shrinkage, because the direction of change in length is influenced by the relative rates of deletions and insertions of genetic material [ 2 ]. (royalsocietypublishing.org)
- Page and colleague Dr Bruce Lahn reconstructed the stages of sex chromosome evolution, and the time course over which these chromosomes were built. (abc.net.au)
- appear
- Most likely this suppression was the result of a series of chromosomal inversions on the Y chromosome, which would also explain why the genes appear to be in order on the X but scrambled on the Y," Page explains. (abc.net.au)
- time
- On the contrary, the length of the W chromosome can fluctuate over short time scales, probably involving both shortening and elongation of non-coding regions. (royalsocietypublishing.org)
- cells
- Female ES cells possess two active X chromosomes and recapitulate random XCI when induced to differentiate. (embopress.org)
- Xist is expressed at very low levels from every X chromosome in both undifferentiated male and female ES cells. (embopress.org)
- regions
- We observe that genetic diversity in the PAR1 is significantly greater than the non-recombining regions (nonPARs). (genetics.org)
- presence
- The presence of these X-Y genes reinforces the idea that the Y chromosome developed from an X-like ancestor. (abc.net.au)
- length
- Each piece of the chromosomes that inverted added to the length of DNA that could no longer align and recombine. (abc.net.au)
- changes
- Here, we analysed karyotypes of 200 bird species to test whether the supposed directional changes occur in bird sex chromosomes. (royalsocietypublishing.org)
- play
- This suggests that chromosome instability and aneuploidy may play a critical role in tumor development and progression ( Sen, 2000 ). (biologists.org)
- Science
- Research published in this week's Science reveals that the Y chromosome developed from an X-like ancestor around 300 million years ago. (abc.net.au)