Pathway: Meiotic synapsis
Reactions in pathway: Meiotic synapsis :
Meiotic synapsis
Meiotic synapsis is the stable physical pairing of homologous chromosomes that begins in leptonema of prophase I and lasts until anaphase of prophase I. First, short segments of axial elements form along chromosomes. Telomeres then cluster at a region of the inner nuclear membrane and axial elements extend and fuse along the length of the chromosomes. Subsequent to the initiation of recombination transverse filaments of SYCP1 link axial/lateral elements to a central element containing SYCE1 and SYCE2, thus forming the synaptonemal complex (reviewed in Yang and Wang 2009).
Unsynapsed regions are silenced during pachynema by recruitment of BRCA1 and ATR, which phosphorylates histone H2AX (reviewed in Inagaki et al. 2010).
Unsynapsed regions are silenced during pachynema by recruitment of BRCA1 and ATR, which phosphorylates histone H2AX (reviewed in Inagaki et al. 2010).
During meiosis the replicated chromosomes of a single diploid cell are segregated into 4 haploid daughter cells by two successive divisions, meiosis I and meiosis II. In meiosis I, the distinguishing event of meiosis, pairs (bivalents) of homologous chromosomes in the form of sister chromatids are paired by synapsis along their regions of homologous DNA (Yang and Wang 2009), and then segregated, resulting in haploid daughters containing sister chromatids paired at their centromeres (Cohen et al. 2006, Handel and Schimenti 2010). The sister chromatids are then separated and segregated during meiosis II.
Recombination between chromosomal homologues but not between sister chromatids occurs during prophase of meiosis I (Inagaki et al. 2010). Though hundreds of recombination events are initiated, most are resolved without crossovers and only tens proceed to become crossovers. In mammals recombination events are required between homologues for normal pairing, synapsis, and segregation.
Human reproduction mixes the genomes of two individuals, creating a new organism. The offspring individuals produced by sexual reproduction differ from their parents and from their siblings. Reproduction includes the reproductive system, sperm and egg production (haploid cells), fertilization, and the early stages embryo development.