Meiosis as a Cause of Mitosis in Plants

Published: 2021-08-01 16:20:07
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Category: Biology, Genetics

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Meiosis in angiosperms (flowering plants) occurs within the floral organs of the plant and is defined by two major features: recombination of the pre-meiotic chromosomes and the reduction of ploidy in half. The ploidy is reduced in half because a single round of DNA replication is followed by two rounds of chromosome segregation and cell division (Crismani et al., 2012; Harrison et al., 2010), as shown in figure 1. Meiosis can be divided in two meiotic divisions, namely meiosis I and meiosis II. Meiosis I is seen as the reductional division, as during meiosis I in a diploid cell, homologous chromosomes pair and replicate after which crossing over occurs. Then, homologous chromosomes segregate to opposite poles, resulting in two haploid cells (Crismani et al., 2012; Harrison et al., 2010; Mezard et al., 2007; Reece et al., 2014; Villeneuve and Hillers, 2001). Meiosis I is followed by meiosis II, where the sister chromatids are separated after replication, visualizing a process mechanically similar to mitosis, resulting in four haploid gametes but with genetic differences (Crismani et al., 2012; Harrison et al., 2010; Mezard et al., 2007; Reece et al., 2014; Villeneuve and Hillers, 2001). Mitosis is a non-reductional cell division (maintaining the number of chromosomes), where sister chromatids are segregated after chromosome replication, giving rise to genetically identical cells.
Thus as a result of mitosis in a diploid cell, diploid daughter cells are produced (Crismani et al., 2012; Harrison et al., 2010; Reece et al., 2014). Meiosis I differs dramatically from mitosis as homologous chromosomes pair and crossing over (CO) occurs during Prophase I, before segregation of the chromosomes during Metaphase I/Anaphase I, while during Meiosis II, the sister chromatids segregate to opposite poles in the same manner as during mitosis (Crismani et al., 2012; Harrison et al., 2010; Mezard et al., 2007; Reece et al., 2014; Villeneuve and Hillers, 2001). Meiosis-specific expression of an endonuclease, called SPO11, causes a large number of double strand breaks (DSBs) along the paired chromosomes. A subset of these DSBs is repaired through recombination pathways which lead to physical exchange between the paired chromosomes (CO) (Grelon et al.,2001; Keeney, 1997; Keeney, 2001; Keeney, 2008). Crossing over events between chromosomes in combination with maternal and paternal chromosome sets segregating independently during meiosis in angiosperms, results in novel combinations of genetic variation which can be transferred via both male and female gametes (Crismani et al., 2012; Harrison et al., 2010; Reece et al., 2014).

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