It is the female sex cell, or female gamete; the male gamete is the sperm. The study of the ovum is included in the science of embryology. The development of a new individual from an unfertilized ovum is called parthenogenesis. In higher animals the ovum differs from the sperm in that it is larger and is nonmotile, a smooth sphere or oval lacking the flagellum of the sperm. Like that of the sperm, its nucleus contains the chromosomes, which bear the hereditary material of the parent. A gamete, ovum or sperm, contains half the number of chromosomes found in the body cells of the parent, i.
Spermatogenesis and oogenesis are both forms of gametogenesis, in which a diploid gamete cell produces haploid sperm and egg cells, respectively. Gametogenesis, the production of sperm and eggs, takes place through the process of meiosis. The production of sperm is called spermatogenesis and the production of eggs is called oogenesis. Oogenesis occurs in the outermost layers of the ovaries. As with sperm production, oogenesis starts with a germ cell, called an oogonium plural: oogonia , but this cell undergoes mitosis to increase in number, eventually resulting in up to one to two million cells in the embryo. A primary oocyte begins the first meiotic division, but then arrests until later in life when it will finish this division in a developing follicle. This results in a secondary oocyte, which will complete meiosis if it is fertilized.
43.3C: Gametogenesis (Spermatogenesis and Oogenesis)
Ovum , plural ova , in human physiology, single cell released from either of the female reproductive organs, the ovaries, which is capable of developing into a new organism when fertilized united with a sperm cell. The outer surface of each ovary is covered by a layer of cells germinal epithelium ; these surround the immature egg cells, which are present in the ovaries from the time of birth. A hollow ball of cells, the follicle , encompasses each ovum. Within the follicle the ovum gradually matures see oogenesis. It takes about four months for a follicle to develop once it is activated.
Fertilization occurs when a sperm and an oocyte egg combine and their nuclei fuse. Because each of these reproductive cells is a haploid cell containing half of the genetic material needed to form a human being, their combination forms a diploid cell. This new single cell, called a zygote , contains all of the genetic material needed to form a human—half from the mother and half from the father. Fertilization is a numbers game. During ejaculation, hundreds of millions of sperm spermatozoa are released into the vagina.