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The spindle checkpoint, also known as the metaphase-to-anaphase transition, the spindle assembly checkpoint (SAC), the metaphase checkpoint, or the mitotic checkpoint, is a cell cycle checkpoint during metaphase of mitosis or meiosis that prevents the separation of the duplicated chromosomes until each chromosome is properly attached to the ...
Meiotic sex chromosome inactivation only happens in male, which may partially be the reason why only Spo11 mutant spermatocytes but not oocytes fail to transition from prophase I to metaphase I. [3] [8] However the asynapsis does not happen only within sex chromosomes, and such transcription regulation was suspended until it was further ...
The SC is composed of proteins like SYCP1, SYCP2, and SYCP3, which work together to stabilize the homologs and promote homologous or meiotic recombination, where homologous chromosomes exchange genetic material. Any flaws in its formation lead to failures in meiotic recombination, chromosome segregation, and the completion of meiosis. [7]
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 .
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 synapsis and recombination during prophase I during meiosis in eukaryotes.
It is referred to as the mitotic spindle during mitosis, a process that produces genetically identical daughter cells, or the meiotic spindle during meiosis, a process that produces gametes with half the number of chromosomes of the parent cell. Besides chromosomes, the spindle apparatus is composed of hundreds of proteins.
Due to this genetic recombination, the offspring have a different set of alleles and genes than their parents do. In the diagram, genes B and b are crossed over with each other, making the resulting recombinants after meiosis Ab, AB, ab, and aB. Thomas Hunt Morgan's illustration of crossing over (1916) A double crossing over
The G2 to M transition is dramatic; there is an all-or-nothing effect, and the transition is irreversible. This is advantageous to the cell because entering mitosis is a critical step in the life cycle of a cell. If it does not fully commit, the cell would run into many issues with partially dividing, ultimately likely leading to the cell's death.