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The NCO/SDSA pathway contributes little to genetic variation, since the arms of the chromosomes flanking the recombination event remain in the parental configuration. Thus, explanations for the adaptive function of meiosis that focus exclusively on crossing-over are inadequate to explain the majority of recombination events.
There are two popular and overlapping theories that explain the origins of crossing-over, coming from the different theories on the origin of meiosis.The first theory rests upon the idea that meiosis evolved as another method of DNA repair, and thus crossing-over is a novel way to replace possibly damaged sections of DNA. [9]
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 ...
Meiosis undergoes two divisions resulting in four haploid daughter cells. Homologous chromosomes are separated in the first division of meiosis, such that each daughter cell has one copy of each chromosome. These chromosomes have already been replicated and have two sister chromatids which are then separated during the second division of ...
Gene conversion is the process by which one DNA sequence replaces a homologous sequence such that the sequences become identical after the conversion. [1] Gene conversion can be either allelic, meaning that one allele of the same gene replaces another allele, or ectopic, meaning that one paralogous DNA sequence converts another.
As reviewed by Uringa et al. [19] the RTEL1 helicase is proposed to regulate recombination during meiosis in the worm Caenorhabditis elegans. RTEL1 is a key protein in repair of DSBs. It disrupts D-loops and is thought to promote NCO outcomes through SDSA. The number of DSBs created during meiosis can substantially exceed the number of final CO ...
Ndt80 is a meiosis-specific transcription factor required for successful completion of meiosis and spore formation. [17] The protein recognizes and binds to the middle sporulation element (MSE) 5'-C[AG]CAAA[AT]-3' in the promoter region of stage-specific genes that are required for progression through meiosis and sporulation.
Pairing of the X and Y chromosomes and crossing over (recombination) between their pseudoautosomal regions appear to be necessary for the normal progression of male meiosis. [16] Thus, those cells in which X-Y recombination does not occur will fail to complete meiosis.