Meiotic COs are formed by the repair of DNA double-strand breaks (DSBs) induced by topoisomerase-like SPO11 and its associated proteins ( Kim and Choi, 2019 Lam and Keeney, 2014). COs also contribute to genetic diversity in populations, which facilitates local adaptation and breeding in animals and plants ( Barton and Charlesworth, 1998). The presence of at least one CO per bivalent is essential for the accurate segregation of homologs and ensures the generation of viable gametes because the absence of CO results in unbalanced chromosome segregation at meiosis I and aneuploid cells. During meiosis in most diploid eukaryotes, homologous chromosomes (homologs) pair to form bivalents and undergo reciprocal exchange of genetic material, called crossover (CO). The process involves a single round of DNA replication and two successive rounds of cell division, with the resulting cells having half the number of chromosomes as the parent cell. Meiosis refers to specialized cell division in sexually reproducing eukaryotes ( Villeneuve and Hillers, 2001). Keywords crossover, fluorescence-tagged lines, genotyping-by-sequencing, interference, meiosis, synaptonemal complex Here, we review advanced approaches that enable precise measurement of the location, frequency, and genomic landscapes of COs in plants, with a focus on Arabidopsis thaliana. Accurate and high-throughput detection of COs is important for our understanding of CO formation and chromosome behavior. CO frequency and distribution are biased along chromosomes, suppressed in centromeres, and controlled by pro-CO, anti-CO, and epigenetic factors. At least one CO between homologs is essential for the first meiotic chromosome segregation, but generally only one and fewer than three inter-homolog COs occur in plants. COs generate genetic variations across generations, profoundly affecting genetic diversity and breeding. Meiotic recombination is initiated by excess formation of DNA double-strand breaks (DSBs), among which a subset are repaired by reciprocal genetic exchange, called crossovers (COs). During meiosis, homologous chromosomes (homologs) pair and undergo genetic recombination via assembly and disassembly of the synaptonemal complex.
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