All in the Family
The family photo in number \(\PageIndex1\) illustrates critical point. Kids in a household resemble your parents and also each other, however the kids are never precisely the same unless castle are identical twins. Every of the kids in the photograph inherited a unique combination of traits native the parents. In this concept, you will certainly learn how this happens. That all starts with sex — sex-related reproduction, that is.
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The procedure that produces haploid gametes is dubbed meiosis. Meiosis is a form of cell department in i beg your pardon the number of chromosomes is decreased by half. The occurs only in particular special cells of an organism. In mammals, Meiosis occurs just in gamete developing cells in ~ the gonads. During meiosis, homologous (paired) chromosomes separate, and haploid cells kind that have actually only one chromosome from each pair. Number \(\PageIndex3\) gives an overview of meiosis.
As you have the right to see from the meiosis diagram, two cell departments occur throughout the as whole process, therefore a full of 4 haploid cells are produced. The two cell departments are referred to as meiosis I and meiosis II. Meiosis I starts after DNA replicates throughout interphase. Meiosis II adheres to meiosis ns without DNA replicating again. Both meiosis I and meiosis II take place in four phases, called prophase, metaphase, anaphase, and also telophase. You might recognize these 4 phases from mitosis, the division of the nucleus that takes place throughout routine cell department of eukaryotic cells.
At the finish of meiosis, four haploid cells have actually been produced, yet the cells are not yet gametes. The cells have to develop prior to they end up being mature gametes qualified of fertilization. The breakthrough of diploid cells right into gametes is called gametogenesis. It differs in between males and females.A gamete produced by a masculine is dubbed a sperm, and the procedure that to produce a mature sperm is referred to as spermatogenesis. Throughout this process, a sperm cell grows a tail and gains the capability to “swim,” choose the human being sperm cell displayed in the figure below. A gamete developed by a mrs is referred to as an egg, and also the procedure that to produce a maturation egg is dubbed oogenesis. Simply one egg is produced from the four haploid cell that result from meiosis. The single egg is a very huge cell, together you deserve to see indigenous the human egg additionally shown in figure \(\PageIndex5\).
Spermatogenesis wake up in the wall of the seminiferous tubules, with stem cells at the perimeter of the tube and the spermatozoa at the lumen of the tube. Immediately under the capsule of the tubule space diploid, undifferentiated cells. This stem cells, called spermatogonia (singular: spermatagonium), go v mitosis through one offspring walking on to distinguish into a sperm cell, if the other provides rise come the following generation that sperm.
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The cell beginning meiosis is referred to as a main oocyte. This cabinet will begin the very first meiotic division, but be arrested in its progress in the first prophase stage. At the moment of birth, all future eggs room in the prophase stage. In ~ adolescence, anterior pituitary hormones reason the advancement of a number of follicles in one ovary. This outcomes in the primary oocyte finishing the very first meiotic division. The cell divides unequally, with most of the to move material and also organelles going come one cell, dubbed a an additional oocyte, and also only one set of chromosomes and a little amount the cytoplasm going come the various other cell. This second cell is referred to as a polar body and also usually dies. A secondary meiotic arrest occurs, this time at the metaphase II stage. In ~ ovulation, this second oocyte will be released and also travel towards the uterus through the oviduct. If the second oocyte is fertilized, the cell proceeds through the meiosis II, completing meiosis, producing a 2nd polar body and a fertilized egg containing all 46 chromosomes of a human being being, half of them comes from the sperm.