Gametogenesis in females is known as oogenesis, and this is going to result in the production of an ovum. An ovum is a female gamete or an egg cell, and it is going to have particular layers that you should be aware of on the outside: the corona radiata, which is the outer layer that the sperm will actually have to penetrate to fertilize the egg, and the zona pellucida, which is a layer of glycoproteins inside the corona. We'll get to what is going on during fertilization in just a little bit.
Oogenesis actually begins before birth. Remember, spermatogenesis doesn't happen until puberty. Oogenesis begins before birth, but doesn't complete. It actually arrests at a certain phase, and then after puberty, will continue. This process actually stops after what's known as menopause. So, oogenesis starts with oogonia. These are female diploid germ cells that will divide by mitosis, and actually begin meiosis prior to birth. They divide by mitosis and form primary oocytes that will start meiosis and then stop at prophase 1. Each one of these primary oocytes is going to be contained in a structure known as a follicle. This follicle is going to not only contain the primary oocyte but also play a role in the menstrual cycle.
We'll talk about the menstrual cycle in more detail in just a moment, but very briefly, each month, basically, in humans, though the cycle is different in other organisms, each month FSH (Follicle Stimulating Hormone) is going to cause the follicle to mature, and it's going to cause the primary oocyte to complete meiosis 1, and then the resulting secondary oocyte will begin meiosis 2. The follicle will rupture and release the ovum, and the remaining structure will form what's known as the corpus luteum. This is a temporary endocrine structure that will release a lot of progesterone and some estradiol, but it will eventually go away.
The secondary oocytes are going to be cells arrested at metaphase 2 of meiosis 2. If they get fertilized by a sperm, they will actually then complete meiosis 2, and then, form the complete egg cell, and join with the sperm. During the process of meiosis, these oocytes are going to form polar bodies. These are basically small haploid cells that result due to unequal cytokinesis during oogenesis. Basically, each meiotic division during this process is going to result in a polar body, and that polar body doesn't develop into anything. So, unlike spermatogenesis, where these meiotic divisions give rise to multiple cells that all will go on to become sperm, in oogenesis, only one cell of the meiotic divisions is going to go on to form the egg cell. As you can see, the first polar body will form as the primary oocyte completes meiosis 1 and forms the secondary oocyte. And when the secondary oocyte completes meiosis 2,
