Germ Line Formation in Drosophila

During oogenesis in the ovary of the mother, polar granules are constructed and tethered to the posterior pole of the oocyte by microtubules.

The polar granules remain here during embryogenesis until the 9^th polar division, when a few nuclei migrate to the posterior pole. (Note: Drosophila zygotes are multinucleate until the 13^th nuclear division).

After the 9^th division, the plasma membrane of the oocyte invaginates at the posterior pole to surround each nucleus. The membrane pinches off and each new cell contains cytoplasm containing these polar granules. These cells are called polar cells and are the first single nucleate cells of Drosophila. It is these cells that will eventually for the germ line.