Table of contents :

  • female reproductive apparatus
  • male reproductive apparatus
  • sexual response cycle

  • To say that eggs grow only in females and sperm grow only in males seems a pretty uncontroversial statement. But Japanese researchers have shown that it's not as simple as that, by nurturing female eggs in the testes of male mice. In a growing mouse embryo, the cells that will become the testes or ovaries, known as germ cells, start out the same in both sexes. In males, a gene on the Y chromosome called Sry switches on about halfway through gestation and prompts these undecided cells to develop into testes containing sperm. Females lack Sry and, by default, develop ovaries and eggs. But if you have a female germ cell surrounded by male cells, it will be influenced by the male signals around it, abandones their genetic legacy and goes through the early stages of sperm development ('testicular eggs'). But some of the female cells lodged in the testes develop partly into eggs able to fuse with sperm, but not to develop into embryosref. A study 25 years ago reported eggs that seemed to grow in male mice, but that was simply based on the shape and size of the cellsref. Okabe's study is the first to use modern genetic techniques to confirm that such cells are genetically female. In Klinefelter syndrome, for example, males carry an additional X chromosome and budding sex cells disappear : the chimeric mice could help explain exactly what happens to these cells and why.

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