Studying recombination in mouse oocytes.

Meiosis is the specialized cell division in sexually reproducing organisms in which haploid gametes are produced. Meiotic prophase I is the defining stage of meiosis, when pairing and synapsis occur between homologous chromosomes, concurrent with reciprocal recombination (or crossing over) events that arise between them. Any disruption of these events during prophase I can lead to improper segregation of homologous chromosomes which can cause severe birth defects in the resulting progeny, and this occurs with alarming frequency in human oocytes. Thus, while the pathways that regulate these events in prophase I are highly conserved in both males and females, the stringency with which these events are monitored and/or controlled appears to be dramatically lower in females. These observations underscore the need to examine and compare meiotic mechanisms across the sexes. However, the study of female meiosis is impeded by the early start of meiosis during fetal development and the very limited amount of ovarian tissue available for meiotic analyses. Here we describe three different techniques which are useful for meiotic prophase I analysis in mouse/human oocytes, ranging from early prophase I events through until the resolution of crossing over at the first and second meiotic divisions.