Double trouble in human aneuploidy

Crossing over, or reciprocal recombination, is essential for accurate segregation of homologous chromosomes at the first meiotic division, resulting in gametes containing the correct chromosome number. A new study in human oocytes analyzes the genome-wide recombination and segregation patterns in all the products of female meiosis, providing experimental support for existing theories about the origin of human aneuploidies and highlighting a novel reverse segregation mechanism of chromosome segregation during meiosis.