A pachytene map of the mouse oocyte.

A map of the mouse oocyte has been constructed utilizing early and mid/late pachytene stages. Each bivalent was clearly identified. At the mid/late stage 195 chromomeres corresponded directly to precursor chromomeres in the early stage, whilst 84 chromomers were derived from two chromomers from the early stage. The X and 13 bivalents were found to have a single chromomere in the early stage which later yielded two sites. There were approximately twice as many total chromomeres as mitotic bands, with good correspondence between pachytene chromomeres and major mitotic bands. Application of the use of mapping to a previously reported bivalent bearing a pleiomorphic region is noted.