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In genetics, a chiasma (pl.: chiasmata) is the point of contact, the physical link, between two (non-sister) chromatids belonging to homologous chromosomes. At a given chiasma, an exchange of genetic material can occur between both chromatids, what is called a chromosomal crossover , but this is much more frequent during meiosis than mitosis ...
The pachytene stage (/ˈpækɪtiːn/ PAK-i-teen; from Greek words meaning "thick threads". [1]: 27 ), also known as pachynema, is the third stage of prophase I during meiosis, the specialized cell division that reduces chromosome number by half to produce haploid gametes.
Achiasmate meiosis refers to meiosis without chiasmata, which are structures that are necessary for recombination to occur and that usually aid in the segregation of non-sister homologs. [1] The pachytene stage of prophase I typically results in the formation of chiasmata between homologous non-sister chromatids in the tetrad chromosomes that ...
The structure, visible by microscopy, is called a bivalent. [5] Resolution of the DNA recombination intermediate into a crossover exchanges DNA segments between the two homologous chromosomes at a site called a chiasma (plural: chiasmata). This physical strand exchange and the cohesion between the sister chromatids along each chromosome ensure ...
This is an accepted version of this page This is the latest accepted revision, reviewed on 26 January 2025. Cell division producing haploid gametes For the figure of speech, see Meiosis (figure of speech). For the process whereby cell nuclei divide to produce two copies of themselves, see Mitosis. For excessive constriction of the pupils, see Miosis. For the parasitic infestation, see Myiasis ...
The term chiasma is linked, if not identical, to chromosomal crossover. Morgan immediately saw the great importance of Janssens' cytological interpretation of chiasmata to the experimental results of his research on the heredity of Drosophila.
Chromatin "sheaths" visible around each SC. Bottom: Two tomato SCs with the chromatin removed, allowing kinetochores ("ball-like" structures) at centromeres to be revealed. The synaptonemal complex ( SC ) is a protein structure that forms between homologous chromosomes (two pairs of sister chromatids ) during meiosis and is thought to mediate ...
Lampbrush chromosomes are clearly visible even in the light microscope, where they are seen to be organized into a series of chromomeres with large chromatin loops extended laterally. Continuous RNA transcription is required to maintain typical chromomere-loop structure of lampbrush chromosomes.