Identifying this role of the Ctf19 complex has paved the way for understanding exactly how DNA breaks are prevented near centromeres. This does not prevent DNA breaks from occurring, but also prevents crossovers. Ctf19 also promotes the enrichment of another protein complex called cohesin near centromeres. This revealed that a protein complex called Ctf19 stops DNA breaks from occurring near the centromere, and so prevents crossovers. examined crossover positioning in budding yeast cells, which are often used as a model to investigate processes such as cell division. However, exactly how crossovers are suppressed at centromeres is not understood. If a crossover does occur in this region, segregation problems are more likely to occur. This can lead to the formation of sex cells that contain the wrong number of chromosome copies, which can cause developmental conditions such as Down’s syndrome.Ĭrossovers tend not to occur at a region of the chromosomes called the centromere, which is where copies of the same chromosome from the same parent are joined together until it is time for them to separate. However, if a crossover occurs in the wrong part of the chromosome, the chromosome copies may not segregate correctly during cell division. During meiosis, different versions of the same chromosome are able to swap sections of their DNA in a process called crossover. Sex cells form in a process called meiosis, where a cell containing two copies of every chromosome duplicates its genetic material and then divides to form four new cells, each of which contains one copy of each chromosome.
CHIASMATA CROSSOVER DEFINITION FULL
However, sex cells (such as egg cells and sperm cells) contain just one copy of every chromosome, so that when they fuse, the new cell that is formed contains the full set. Most cells contain two copies of each chromosome – one inherited from each parent.
The cells of animals, plants and many other organisms store most of their DNA inside the cell nucleus, packaged into structures called chromosomes. This non-canonical role of the kinetochore in defining a chromosome domain that is refractory to crossovers adds a new layer of functionality by which the kinetochore prevents the incidence of chromosome segregation errors that generate aneuploid gametes. The Ctf19 complex independently drives the enrichment of cohesin throughout the broader pericentromere to suppress crossovers, but not DNA breaks. The Ctf19 complex prevents meiotic DNA break formation, the initiating event of recombination, proximal to the centromere. We uncover multi-layered suppression of pericentromeric recombination by the Ctf19 complex, operating across distinct chromosomal distances.
Here, we identify the conserved Ctf19/CCAN kinetochore sub-complex as a major factor that minimizes potentially deleterious centromere-proximal crossovers in budding yeast. Crossover recombination is non-random across the genome, and centromere-proximal crossovers are associated with an increased risk of aneuploidy, including Trisomy 21 in humans. During meiosis, crossover recombination is essential to link homologous chromosomes and drive faithful chromosome segregation.
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