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The normal separation of chromosomes in meiosis I or sister chromatids in meiosis II is termed disjunction. When the segregation is not normal, it is called nondisjunction . This results in the production of gametes which have either too many or too few of a particular chromosome, and is a common mechanism for trisomy or monosomy .
Chromosome decondensation (also known as relaxation or decompaction) into expanded chromatin is necessary for the cell's resumption of interphase processes, and occurs in parallel to nuclear envelope assembly during telophase in many eukaryotes. [2] MEN-mediated Cdk dephosphorylation is necessary for chromosome decondensation. [2] [5]
Chromosome segregation is the process in eukaryotes by which two sister chromatids formed as a consequence of DNA replication, or paired homologous chromosomes, separate from each other and migrate to opposite poles of the nucleus. This segregation process occurs during both mitosis and meiosis. Chromosome segregation also occurs in prokaryotes ...
During the leptotene stage, the duplicated chromosomes - each consisting of two sister chromatids - condense from diffuse chromatin into long, thin strands that are more visible within the nucleoplasm (nucleus contents). The chromosomes become visible as thin threadlike structures known as leptonema under a light microscope. [1]: 27 [2]: 353
Cell division in prokaryotes (binary fission) and eukaryotes (mitosis and meiosis). The thick lines are chromosomes, and the thin blue lines are fibers pulling on the chromosomes and pushing the ends of the cell apart. The cell cycle in eukaryotes: I = Interphase, M = Mitosis, G 0 = Gap 0, G 1 = Gap 1, G 2 = Gap 2, S = Synthesis, G 3 = Gap 3.
Condensins also play important roles in chromosome assembly and segregation in meiosis. Genetic studies have been reported in S. cerevisiae, [72] D. melanogaster, [73] [74] and C. elegans. [75] In mice, requirements for condensin subunits in meiosis have been addressed by antibody-mediated blocking experiments [58] and conditional gene knockout ...
McClintock used the prophase and metaphase stages of mitosis to describe the morphology of corn's chromosomes, and later showed the first ever cytological demonstration of crossing over in meiosis. Working with student Harriet Creighton, McClintock also made significant contributions to the early understanding of codependency of linked genes.
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.