Models of Recombination

Abstract

At meiosis, each member of a pair of homologous chromosomes replicates to form two sister chromosomes known as chromatids. The maternally and paternally derived sister pairs then perfectly align to form a bundle of four chromatids. Crossing-over occurs at points along the bundle known as chiasmata. At each chiasma, one sister chromatid from each pair is randomly selected and cut at the crossover point. The cell then rejoins the partial paternal chromatid above the cut to the partial maternal chromatid below the cut, and vice versa, to form two hybrid maternal-paternal chromatids. The preponderance of evidence suggests that the two chromatids participating in a chiasma are chosen nearly independently from chiasma to chiasma [30]. This independence property is termed lack of chromatid interference. After crossing-over has occurred, the recombined chromatids of a bundle are coordinately separated by two cell divisions so that each of the four resulting gametes receives exactly one chromatid.