Genome-wide maps of recombination and chromosome segregation in human oocytes and embryos show selection for maternal recombination rates.

Abstract

Crossover recombination reshuffles genes and prevents errors in segregation that lead to extra or missing chromosomes (aneuploidy) in human eggs, a major cause of pregnancy failure and congenital disorders. Here, we generate genome-wide maps of crossovers and chromosome segregation patterns by recovering all three products of single female meioses. Genotyping > 4 million informative single-nucleotide polymorphisms (SNPs) from 23 complete meioses allowed us to map 2,032 maternal and 1,342 paternal crossovers and to infer the segregation patterns of 529 chromosome pairs. We uncover a novel reverse chromosome segregation pattern in which both homologs separate their sister chromatids at meiosis I; detect selection for higher recombination rates in the female germline by the elimination of aneuploid embryos; and report chromosomal drive against non-recombinant chromatids at meiosis II. Collectively, our findings reveal that recombination not only affects homolog segregation at meiosis I but also the fate of sister chromatids at meiosis II.