A study of meiotic germ cells in the gonads of foetal mouse chimaeras

Abstract

ABSTRACT The gonads of 53 foetuses (16♀, 37♂) derived from fusion of embryos at about the 8-cell stage were examined. Ovotestes were found in two of the male foetuses. When gonads were sectioned days post coitum, germ cells in meiotic prophase were seen in 6/6 female and 4/14 male foetuses. When air-dried preparations were made from gonads days post coitum, germ cells in meiotic prophase were seen in 7/7 females and 4/13 males. At days post coitum, 2/2 female but only 2/10 male foetuses showed any meiotic cells, and these were degenerating. [3H]Thymidine injected into the mother days post coitum resulted in labelling of the meiotic germ cells, but the sex vesicle characteristic of meiotic cells in normal males was never seen. The timing of DNA synthesis and meiosis was identical to that seen in the germ cells in foetal ovaries. We conclude that the meiotic cells seen in the testes of foetal chimaeras are probably XX in constitution, and rarely survive beyond the 19th day of gestation.