Meiosis Chromatids

Vande Woude It is homologous in meiosis versus sister chromatids that CSF works on. 

Klein F, Mahr P, Galova M et al 1999 A central role for cohesins in sister chromatid cohesion, formation of axial elements, and recombination during yeast meiosis. Cell 98 91-103... 

Miyazaki WY, Orr-Weaver TL 1994 Sister chromatid cohesion in mitosis and meiosis. Annu Rev Genet 28 167-187... 

Rattner JB 1991 The structure of the mammalian centromere. Bioessays 13 51-56 Rieder CL, Cole R 1999 Chromatid cohesion during mitosis lessons from meiosis. J Cell Sci 112 2607-2613... 

Phosphorylation has been thought to be correlated to the mitotic chromatin condensation and the transcriptional regulation in interphase (Nowak and Corces, 2004). The mitotic phosphorylation, which was first identified in 1978 (Gurley et al, 1978), occurs at Ser (Wei et al, 1998), Ser (Goto et al, 1999), and Thr (Preuss et al, 2003) in histone H3. The Ser phosphorylation is catalyzed by the aurora kinase family (de la Barre et al, 2000), and is required for the initiation of chromosome condensation but not for its maintenance (dephosphorylation of mitotic chromosomes does not induce chromosome decondensation) (Van Hooser et fl/.,1998). In meiosis, Ser phosphorylation is also required for the cohesion of sister chromatids rather than the condensation (Kaszas and Cande, 2000). 

Karymov MA, Tomschik M, Leuba SH, Caiafa P, Zlatanova J (2001) DNA methylation-dependent chromatin fiber compaction in vivo and in vitro requirement for hnker histone. Faseb J 15 2631—2641 Kaszas E, Cande WZ (2000) Phosphorylation of histone H3 is correlated with changes in the maintenance of sister chromatid cohesion during meiosis in maize, rather than the condensation of the chromatin. J Cell Sci 113(Pt 18) 3217-3226... 

This reduction is achieved through meiosis, a process in which two successive ceU divisions occur without intervening DNA duplication. As with the cell cycle, DNA duphcation wiU have aheady taken place prior to the cell division, so that during the initial prophase each pair of identical DNA molecules forms a pair of chromatids attached to each other at a centrosome. In contrast to mitosis, however, homologous chromosomes now pair up (metaphase I). Note that in a pair of homologous chromosomes each wiU contain the same genes (one of the pair having come from the mother and one from the father) but many of the alleles wiU be different. 

Figure 6.45 Crossover at meiosis. Two homologous chromosomes are shown aligned in the top line. Each consists of two chromatids, joined together at the centromere. A and B represent genes on one chromosome, and a and b the corresponding alleles on the other chromosome. After recombination two new gene combinations are apparent. The middle and bottom lines represent other possible methods of recombination. Source From Refs. 12 and 13.

During the prophase of the first meiotic division (meiosis I) two homologous pairs of partially "condensed" chromosomes must find each other and pair with appropriate orientation. A protein in the telomeres of the chromosomes seems to be involved.269 277 The key structure in meiotic crossing-over is the ribbonlike synaptonemal complex formed by the pairs of homologous chroma fids.271/278 2791 This complex, in which a proteinaceous core or axial element separates the greatly extended chromatid pairs (Fig. 26-13), is fully formed in the pachytene stage of meiosis. Formation of the synaptonemal complex is preceded by development of a few double-stranded breaks in... 

Mismatch repair was an essential component of the Holliday model for meiotic recombination in fungi (Holliday, 1965a). This states that recombination depends on the formation of relatively short stretches of hybrid DNA between homologous chromatids within which, if they spanned a region of heterozygosity, a mispaired base-pair would appear. Mismatch repair would determine whether or not aberrant segregations would be found in the tetrads formed on completion of meiosis. 

In the fine structure of cells, microtubules make up fibers such as the spindle fibers that attach to centromeres of chromosomes to pull chromatids apart during mitosis and meiosis. Microtubules function in a number of cellular processes, including motility of cells and subcellular components. Microtubules assemble into tubulin, a substance that can change the shape of cells. 

NONDISJUNCTION The failure of homologous chromosomes to separate at anaphase I of meiosis the failure of chromatids to separate at anaphase of mitosis or at anaphase II of meiosis. 

A FIGURE 9-45 Recombination during meiosis. (a) Crossing over can occur between chromatids of homologous chromosomes before the first meiotic division (see Figure 9-3). 

---