Zygotene
Zygotene(from greek "paired threads"[1]) is the second stage ofprophase Iduringmeiosis,the specialized cell division that reduces the chromosome number by half to produce haploid gametes. It follows theLeptotene stageand is followed byPachytene stage.
Synapsis completion
[edit]The key event during zygotene is the completion of synapsis betweenhomologous chromosomes.Synapsis began during the previous leptotene stage, with the homologous chromosomes starting to pair together and associate lengthwise, facilitated by the synaptonemal complex protein structure.[2]
In zygotene, the synaptonemal complex forms more extensively between the paired chromosomes. It zips the homologs together along their entire length, with the lateral elements of the complex associated with each chromosome and the central region holding them together. This allows intimate pairing and genetic recombination events.[3][4]
Chromosome condensation
[edit]The chromosomes continue condensing during zygotene into distinct threadlike structures. Each chromosome now appears thicker as the sister chromatids are closely aligned.[5]
Recombination nodules
[edit]As synapsis completes, proteinaceous recombination nodules begin to appear along the synaptonemal complex between the homologous chromosomes. These represent sites of genetic crossover events, where exchange of chromosomal segments occurs between the non-sister chromatids.[6][7]
Key recombination proteins like MLH1/3 and MSH4/5 mark the sites of crossover formation. The number and positioning of these crossovers is regulated to ensure at least one crossover per chromosome arm for proper segregation in later meiotic stages.[8]
Transition to pachytene
[edit]Once synapsis and crossing over are complete, the cell transitions to thepachytenestage of prophase I. Pachytene features fully condensed and paired chromosomes along their length, with distinctly visible recombination nodules.[9][10]
Importance
[edit]The zygotene stage is crucial for genetic recombination and proper chromosome segregation in meiosis.[1]Defects in synapsis, recombination, or crossover regulation can lead to aneuploidy and chromosomal abnormalities in gametes.[11]
References
[edit]- ^ab"Stages of Meiosis and Sexual Reproduction | Learn Science at Scitable".Nature.com.Retrieved2024-05-08.
- ^Wang, Yingxiang; Cheng, Zhukuan; Ma, Hong (2013), Assmann, Sarah; Liu, Bo (eds.),"Meiosis: Interactions Between Homologous Chromosomes",Cell Biology,New York, NY: Springer, pp. 1–34,doi:10.1007/978-1-4614-7881-2_18-1,ISBN978-1-4614-7881-2,retrieved2024-02-15
- ^Qiao, Huanyu; Chen, Jefferson K.; Reynolds, April; Höög, Christer; Paddy, Michael; Hunter, Neil (2012-06-28)."Interplay between Synaptonemal Complex, Homologous Recombination, and Centromeres during Mammalian Meiosis".PLOS Genetics.8(6): e1002790.doi:10.1371/journal.pgen.1002790.ISSN1553-7390.PMC3386176.PMID22761591.
- ^Zhang, Feng-Guo; Zhang, Rui-Rui; Gao, Jin-Min (2021-09-14)."The organization, regulation, and biological functions of the synaptonemal complex".Asian Journal of Andrology.23(6): 580–589.doi:10.4103/aja202153.ISSN1008-682X.PMC8577265.PMID34528517.
- ^Zickler, D.; Kleckner, N. (1998-01-01)."The leptotene-zygotene transition of meiosis".Annual Review of Genetics.32:619–626.doi:10.1146/annurev.genet.32.1.619.PMID9928494.
- ^Zhang, Fengguo; Liu, Mengfei; Gao, Jinmin (2022)."Alterations in synaptonemal complex coding genes and human infertility".International Journal of Biological Sciences.18(5): 1933–1943.doi:10.7150/ijbs.67843.ISSN1449-2288.PMC8935243.PMID35342360.
- ^Naranjo, Tomás (2012)."Finding the Correct Partner: The Meiotic Courtship".Scientifica.2012:509073.doi:10.6064/2012/509073.ISSN2090-908X.PMC3820632.PMID24278707.
- ^Zickler, Denise; Kleckner, Nancy (2015)."Recombination, Pairing, and Synapsis of Homologs during Meiosis".Cold Spring Harbor Perspectives in Biology.7(6): a016626.doi:10.1101/cshperspect.a016626.ISSN1943-0264.PMC4448610.PMID25986558.
- ^Azumi, Y. (2002-06-17)."Homolog interaction during meiotic prophase I in Arabidopsis requires the SOLO DANCERS gene encoding a novel cyclin-like protein".The EMBO Journal.21(12): 3081–3095.doi:10.1093/emboj/cdf285.PMC126045.PMID12065421.
- ^"Pachytene - an overview | ScienceDirect Topics".www.sciencedirect.com.Retrieved2024-02-15.
- ^Saito, Takamune T.; Colaiácovo, Monica P. (2017)."Regulation of crossover frequency and distribution during meiotic recombination".Cold Spring Harbor Symposia on Quantitative Biology.82:223–234.doi:10.1101/sqb.2017.82.034132.ISSN0091-7451.PMC6542265.PMID29222342.