Molecular Cartography: Mapping the Landscape of Meiotic Recombination

Meiosis is the specialized cell division that gives rise to gametes (reproductive cells such as sperm or eggs, or spores in yeast). To complete meiosis, a cell duplicates its chromosomes once but then goes through two rounds of chromosome segregation, reducing the genome by half. The original chromosome number is restored by the fusion of gametes during fertilization to form a zygote. Meiosis is a fundamental bottleneck passed by each generation in a sexually reproducing organism (Figure 1). In the first meiotic division, homologous maternal and paternal chromosomes are separated, whereas sister chromatids—the pair resulting from chromosome replication prior to meiosis—are separate in the second division [2] (Figure 1B). During meiosis in most organisms, genetic information is exchanged between chromosomes through homologous recombination, which serves important biological functions. At the genomic level, recombination creates diversity by reshuffling genetic information between homologous chromosomes. At the cellular level, recombination generates temporary connections between homologous chromosomes that are required for accurate segregation [3]. Alterations in the normal recombination pattern are often associated with errors in chromosome segregation in humans, and these errors are a major cause of spontaneous abortions and congenital birth defects, including mental retardation [4].