All in the Family

The family photo in figure (PageIndex1) illustrates critical point. Youngsters in a family resemble their parents and also each other, yet the kids are never exactly the very same unless they are identical twins. Every of the youngsters in the picture inherited a unique mix of traits from the parents. In this concept, you will certainly learn how this happens. That all starts with sex — sex-related reproduction, that is.

You are watching: What process maintains a constant number of chromosomes in a species

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Meiosis

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Figure (PageIndex3): rundown of Meiosis. During meiosis, homologous chromosomes separate and also go to various daughter cells. This diagram shows simply the nuclei the the cells. Notification the exchange of hereditary material the occurs before the very first cell division.

The process that produces haploid gametes is referred to as meiosis. Meiosis is a form of cell division in i beg your pardon the variety of chromosomes is diminished by half. It occurs just in particular special cells of an organism. In mammals, Meiosis occurs just in gamete producing cells in ~ the gonads. Throughout meiosis, homologous (paired) chromosomes separate, and haploid cells type that have actually only one chromosome from each pair. Number (PageIndex3) gives an overview of meiosis.

As you have the right to see native the meiosis diagram, 2 cell departments occur throughout the as whole process, so a complete of four haploid cells room produced. The two cell departments are dubbed meiosis I and meiosis II. Meiosis I starts after DNA replicates during interphase. Meiosis II adheres to meiosis ns without DNA replicating again. Both meiosis I and meiosis II occur in 4 phases, referred to as prophase, metaphase, anaphase, and telophase. You may recognize these four phases from mitosis, the department of the nucleus that takes place during routine cell department of eukaryotic cells.


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api/deki/files/18053/Sperm-egg.jpg?revision=1&size=bestfit&width=291&height=197" />Figure (PageIndex5): A human being sperm is a tiny cell v a tail. A human egg is much larger. Both cells are mature haploid gametes that are capable of fertilization. What procedure is displayed in this photograph?

At the end of meiosis, four haploid cells have actually been produced, but the cells room not however gametes. The cells must develop before they come to be mature gametes capable of fertilization. The advance of diploid cells into gametes is called gametogenesis. That differs between males and also females.

A gamete developed by a masculine is dubbed a sperm, and the process that produces a maturation sperm is dubbed spermatogenesis. Throughout this process, a sperm cell grows a tail and gains the capacity to “swim,” choose the human being sperm cell shown in the number below. A gamete created by a mrs is called an egg, and the procedure that produce a maturation egg is referred to as oogenesis. Just one egg is developed from the 4 haploid cell that an outcome from meiosis. The single egg is a very large cell, as you have the right to see from the human egg additionally shown in figure (PageIndex5).
Spermatogenesis

Spermatogenesis occurs in the wall surface of the seminiferous tubules, with stem cells in ~ the perimeter of the tube and the spermatozoa in ~ the lumen of the tube. Immediately under the capsule of the tubule space diploid, regardless of cells. These stem cells, referred to as spermatogonia (singular: spermatagonium), go through mitosis with one offspring walk on to identify into a sperm cell, if the other offers rise to the next generation of sperm.

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api/deki/files/15863/Figure_43_03_06.jpg?revision=1" />Figure (PageIndex7): Oogenesis The procedure of oogenesis wake up in the ovary"s outermost layer. A major oocyte begins the first meiotic department but climate arrests until later on in life when it will end up this division in a arising follicle. This results in a second oocyte, i m sorry will finish meiosis if it is fertilized.

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The cell beginning meiosis is called a primary oocyte. This cabinet will start the very first meiotic division, but be arrested in its progression in the an initial prophase stage. At the moment of birth, all future eggs room in the prophase stage. In ~ adolescence, anterior pituitary hormones cause the advance of a variety of follicles in one ovary. This outcomes in the major oocyte finishing the first meiotic division. The cell divides unequally, with many of the to move material and also organelles going to one cell, called a second oocyte, and also only one set of chromosomes and a tiny amount the cytoplasm going to the other cell. This 2nd cell is referred to as a polar body and usually dies. A secondary meiotic arrest occurs, this time at the metaphase II stage. In ~ ovulation, this secondary oocyte will be released and travel towards the uterus v the oviduct. If the secondary oocyte is fertilized, the cell proceeds through the meiosis II, perfect meiosis, creating a second polar body and also a fertilized egg containing all 46 chromosomes that a person being, half of them comes from the sperm.