Meiotic Recombination Pathways

Abstract

During meiosis, one round of DNA replication is followed by two rounds of division to create the gametes that are obligatory for biparental reproduction. To achieve the reductional segregation that is required during the first meiotic division, most eukaryotes utilise a program that involves the deliberate formation of DNA double‐stranded breaks in their genomes, followed by regulated homologous recombination and reciprocal exchange of genetic material between homologous chromosomes. This reciprocal exchange of genetic information physically links the homologous chromosomes to one another and provides the tension that is necessary for their segregation. Meiotic recombination is highly regulated to ensure that at least one reciprocal crossover event occurs between each pair of homologous chromosomes. Key Concepts Meiotic recombination physically links the homologous chromosomes to one another, creating the tension that is required for their segregation. Meiosis I is a reductional segregation that halves the ploidy of the cell. This process requires bi‐orientation of the homologous chromosomes but mono‐orientation of the sister chromatids, a feat that is achieved through structural modification of the sister chromatid centromeres by monopolin. Directed homologous recombination physically links the homologous chromosomes to one another, through preferential use of the homologous chromosome as the repair template, rather than the sister chromatid, followed by resolution of the recombination intermediate into a crossover. DNA double‐stranded break fate is decided early in the meiotic recombination pathway, with crossovers exclusively arising through a double‐Holliday junction intermediate and non‐crossovers primarily being formed through the synthesis‐dependent strand annealing pathway. Formation of the synaptonemal complex, a proteinaceous structure that assembles between homologous chromosomes during meiosis, is interdependent with meiotic recombination.