The number of potential sites of crossing over, represented by double strand breaks (DSBs), is always far greater than the number of eventual crossovers, and is presumably regulated genetically and epigenetically at the whole-genome level ( Wang and Copenhaver, 2018 Modliszewski et al., 2018). A single crossover between two homologues ensures their normal behaviour in meiosis. On the other hand, a mechanism of crossover assurance guarantees that each pair of homologues gets at least one, the so-called obligatory crossover ( Jones, 1984 John, 1990 Hillers, 2004 Jones and Franklin, 2006). This control is exercised via positive crossover interference which, in essence, has a suppressive effect on the formation of another crossover in the vicinity of an already established crossover. As such, crossovers are under strict genetic control, for both their number and distribution. Chiasmata, the cytological expression of crossing over, form mechanical connections between homologous chromosomes during the first meiotic division and hence are essential elements of an orderly reduction of the chromosome number. Meiotic division is an integral part of sexual reproduction it maintains stable chromosome numbers over generations. Chromatid interference has to be seriously addressed in genetic mapping approaches and further studies.Ĭentromere, chromatid interference, crossover interference, homoeologous chromosome, hybrid, meiosis, recombination Introduction The two arms of a chromosome appear to act as independent units in the process of crossing over. We also provide a physical measure of the crossover interference distance, covering ~30–40% of the relative chromosome arm length, and show that the centromere acts as a barrier for crossover interference. roylei) during anaphase I, we demonstrate that the involvement of four chromatids in double crossovers is significantly more frequent than expected (64% versus 25%).
Using in situ probing in two interspecific plant hybrids ( Lolium multiflorum×Festuca pratensis and Allium cepa×A. Here, we provide direct evidence of chromatid interference. Such analyses are possible in very few organisms as they require observation of all four products of a single meiosis. A poorly studied aspect of the control is chromatid interference. The well-known crossover control is positive crossover interference which reduces the probability of a crossover in the vicinity of an already formed crossover. As such, it is strictly controlled in frequency and distribution. Hence, it is responsible for an orderly reduction of the chromosome number. Crossing over, in addition to its strictly genetic role, also performs a critical mechanical function, by bonding homologues in meiosis.
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