This continues into old age. Figure 2. Oogenesis, illustrated in Figure 2, 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 about one to two million cells in the embryo.
The cell starting meiosis is called a primary oocyte, as shown in Figure 2. This cell will start the first meiotic division and be arrested in its progress in the first prophase stage. At the time of birth, all future eggs are in the prophase stage.
At adolescence, anterior pituitary hormones cause the development of a number of follicles in an ovary. This results in the primary oocyte finishing the first meiotic division. The cell divides unequally, with most of the cellular material and organelles going to one cell, called a secondary oocyte, and only one set of chromosomes and a small amount of cytoplasm going to the other cell.
This second cell is called a polar body and usually dies. A secondary meiotic arrest occurs, this time at the metaphase II stage. At ovulation, this secondary oocyte will be released and travel toward the uterus through the oviduct. Stem cells are deposited during gestation and are present at birth through the beginning of adolescence, but in an inactive state. During adolescence, gonadotropic hormones from the anterior pituitary cause the activation of these cells and the production of viable sperm.
This continues into old age. Learning Objectives Distinguish between spermatogenesis and oogenesis. Key Points Gametogenesis, the production of sperm spermatogenesis and eggs oogenesis , takes place through the process of meiosis. In oogenesis, diploid oogonium go through mitosis until one develops into a primary oocyte, which will begin the first meiotic division, but then arrest; it will finish this division as it develops in the follicle, giving rise to a haploid secondary oocyte and a smaller polar body.
The secondary oocyte begins the second meiotic division and then arrests again; it will not finish this division unless it is fertilized by a sperm; if this occurs, a mature ovum and another polar body is produced.
In spermatogenesis, diploid spermatogonia go through mitosis until they begin to develop into gametes; eventually, one develops into a primary spermatocyte that will go through the first meiotic division to form two haploid secondary spermatocytes.
The secondary spermatocytes will go through a second meiotic division to each produce two spermatids; these cells will eventually develop flagella and become mature sperm.
Key Terms spermatocyte : a male gametocyte, from which a spermatozoon develops oocyte : a cell that develops into an egg or ovum; a female gametocyte polar body : one of the small cells that are by-products of the meiosis that forms an egg mitosis : the division of a cell nucleus in which the genome is copied and separated into two identical halves.
It is normally followed by cell division meiosis : cell division of a diploid cell into four haploid cells, which develop to produce gametes. Gametogenesis Spermatogenesis and Oogenesis Gametogenesis, the production of sperm and eggs, takes place through the process of meiosis.
Oogenesis Oogenesis occurs in the outermost layers of the ovaries. 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. Classification 4. Cladistics 6: Human Physiology 1. Digestion 2. The Blood System 3. Disease Defences 4. Gas Exchange 5. Homeostasis Higher Level 7: Nucleic Acids 1. DNA Structure 2. Transcription 3. Translation 8: Metabolism 1. Metabolism 2. Cell Respiration 3.
Photosynthesis 9: Plant Biology 1. Xylem Transport 2. Phloem Transport 3. Plant Growth 4. Plant Reproduction Genetics 1. Meiosis 2. Inheritance 3.
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