How Many Different Babies You Can Have in Meiosis

7.v: Sexual Reproduction: Meiosis and gametogenesis

1. Last updated

2. Save as PDF

Page ID

16757

• 
• Professors (Cell Molecular Biology & Constitute Science) at Butte College
• Source: link

All in the Family

The family photo in Figure \(\PageIndex{1}\) illustrates an of import bespeak. Children in a family resemble their parents and each other, only the children are never exactly the same unless they are identical twins. Each of the children in the photo inherited a unique combination of traits from the parents. In this concept, y'all will learn how this happens. It all begins with sex — sexual reproduction, that is.

Figure \(\PageIndex{i}\): Family photo

Sexual Reproduction

Why do you look like to your parents, but not identical? First, it is considering you have two parents. 2d, it is because of sexual reproduction. Whereas asexual reproduction produces genetically identical clones, sexual reproduction produces genetically various individuals. Sexual reproduction is the creation of a new organism by combining the genetic textile of two organisms. Equally both parents contribute half of the new organism's genetic material, the offspring will have traits of both parents, simply will not exist exactly like either parent.

Figure \(\PageIndex{two}\): Crossing over occurs during meiosis I, and is the process where homologous chromosomes pair upwards with each other and exchange different segments of their genetic material to form recombinant chromosomes. In some species crossing over is essential for the normal segregation of chromosomes during meiosis. Crossing over also increases genetic variation, considering due to the swapping of genetic material during crossing over, the chromatids held together past the centromere are no longer identical. So, when the chromosomes become on to meiosis II and split up, some of the daughter cells receive girl chromosomes with recombined alleles. Due to this genetic recombination, the offspring accept a different set of alleles and genes than their parents practise. In the diagram, genes B and b are crossed over with each other, making the resulting recombinants after meiosis Ab, AB, ab, and aB.fifty.

Organisms that reproduce sexually past joining gametes, a procedure known as fertilization, must have a mechanism to produce haploid gametes. This mechanism is meiosis, a type of cell division that halves the number of chromosomes. During meiosis, the pairs of chromosomes carve up and segregate randomly to produce gametes with ane chromosome from each pair. Meiosis involves two nuclear and cell divisions without interphase in between, starting with one diploid cell and generating four haploid cells. Each division, named meiosis I and meiosis II, has four stages: prophase, metaphase, anaphase, and telophase. These stages are similar to those of mitosis, but there are distinct and important differences.

Prior to meiosis, the cell's DNA is replicated, generating chromosomes with two sister chromatids. A man cell prior to meiosis will have 46 chromosomes, 22 pairs of homologous autosomes, and 1 pair of sexual practice chromosomes. Homologous chromosomes (Figure \(\PageIndex{2}\)), or homologs, are similar in size, shape, and genetic content; they incorporate the aforementioned genes, though they may have unlike alleles of those genes. The genes/alleles are at the same loci on homologous chromosomes. You lot inherit one chromosome of each pair of homologs from your mother and the other 1 from your male parent. Sexual reproduction is the master method of reproduction for the vast majority of multicellular organisms, including almost all animals and plants. Fertilization joins two haploid gametes into a diploid zygote, the start prison cell of a new organism. The zygote enters G1 of the first prison cell cycle, and the organism begins to grow and develop through mitosis and jail cell division.

Meiosis

Figure \(\PageIndex{3}\): Overview of Meiosis. During meiosis, homologous chromosomes separate and get to dissimilar daughter cells. This diagram shows merely the nuclei of the cells. Notice the exchange of genetic material that occurs prior to the first cell division.

The process that produces haploid gametes is chosen meiosis. Meiosis is a type of cell partition in which the number of chromosomes is reduced by half. Information technology occurs simply in certain special cells of an organism. In mammals, Meiosis occurs only in gamete producing cells within the gonads. During meiosis, homologous (paired) chromosomes divide, and haploid cells form that take merely one chromosome from each pair. Figure \(\PageIndex{3}\) gives an overview of meiosis.

Every bit you can run across from the meiosis diagram, ii prison cell divisions occur during the overall process, so a total of four haploid cells are produced. The two cell divisions are chosen meiosis I and meiosis Ii. Meiosis I begins later on Deoxyribonucleic acid replicates during interphase. Meiosis II follows meiosis I without Dna replicating over again. Both meiosis I and meiosis Two occur in 4 phases, chosen prophase, metaphase, anaphase, and telophase. You may recognize these four phases from mitosis, the sectionalisation of the nucleus that takes place during routine cell division of eukaryotic cells.

Figure \(\PageIndex{four}\): Complete Stages of Meiosis: An creature jail cell with a diploid number of four (2n = iv) proceeds through the stages of meiosis to course four haploid daughter cells.

Meiosis I

1. Prophase I: The nuclear envelope begins to suspension downwards, and the chromosomes condense. Centrioles start moving to opposite poles of the cell, and a spindle begins to form. Chiefly, homologous chromosomes pair upwards, which is unique to prophase I. In prophase of mitosis and meiosis II, homologous chromosomes do not form pairs in this style. During prophase I, crossing-over occurs. The significance of crossing-over is discussed in the next section called variations.
2. Metaphase I: Spindle fibers attach to the paired homologous chromosomes. The paired chromosomes line up forth the equator of the jail cell. This occurs simply in metaphase I. In metaphase of mitosis and meiosis II, it is sister chromatids that line up along the equator of the cell.
3. Anaphase I: Spindle fibers shorten, and the chromosomes of each homologous pair offset to separate from each other. One chromosome of each pair moves toward i pole of the cell, and the other chromosome moves toward the opposite pole.
4. Telophase I and Cytokinesis: The spindle breaks down, and new nuclear membranes class. The cytoplasm of the cell divides, and two haploid daughter cells result. The daughter cells each take a random assortment of chromosomes, with one from each homologous pair. Both girl cells go on to meiosis Two.

Meiosis 2

1. Prophase II: The nuclear envelope breaks down and the spindle begins to grade in each haploid daughter jail cell from meiosis I. The centrioles as well start to split.
2. Metaphase Ii: Spindle fibers line upwardly the sister chromatids of each chromosome forth the equator of the cell.
3. Anaphase Ii: Sister chromatids separate and movement to opposite poles.
4. Telophase 2 and Cytokinesis: The spindle breaks downwards, and new nuclear membranes form. The cytoplasm of each cell divides, and 4 haploid cells effect. Each cell has a unique combination of chromosomes.

Gametogenesis

Figure \(\PageIndex{5}\): A human sperm is a tiny cell with a tail. A man egg is much larger. Both cells are mature haploid gametes that are capable of fertilization. What process is shown in this photograph?

At the end of meiosis, iv haploid cells have been produced, just the cells are not still gametes. The cells need to develop before they go mature gametes capable of fertilization. The development of diploid cells into gametes is called gametogenesis. It differs between males and females.

• A gamete produced by a male is called a sperm, and the procedure that produces a mature sperm is chosen spermatogenesis. During this process, a sperm prison cell grows a tail and gains the power to "swim," like the man sperm cell shown in the figure below.
• A gamete produced by a female is chosen an egg, and the process that produces a mature egg is called oogenesis. Just one egg is produced from the four haploid cells that result from meiosis. The unmarried egg is a very large cell, as you tin can see from the human egg also shown in Figure \(\PageIndex{five}\).

Spermatogenesis

Spermatogenesis occurs in the wall of the seminiferous tubules, with stem cells at the periphery of the tube and the spermatozoa at the lumen of the tube. Immediately nether the capsule of the tubule are diploid, undifferentiated cells. These stem cells, called spermatogonia (singular: spermatagonium), go through mitosis with ane offspring going on to differentiate into a sperm cell, while the other gives ascension to the next generation of sperm.

Effigy \(\PageIndex{6}\): Spermatogenesis During spermatogenesis, iv sperm result from each primary spermatocyte, which divides into 2 haploid secondary spermatocytes; these cells will become through a second meiotic division to produce iv spermatids.

Meiosis begins with a cell called a primary spermatocyte. At the cease of the kickoff meiotic sectionalization, a haploid cell is produced chosen a secondary spermatocyte. This haploid cell must become through another meiotic cell sectionalization. The cell produced at the end of meiosis is called a spermatid. When it reaches the lumen of the tubule and grows a flagellum (or "tail"), information technology is chosen a sperm cell. Four sperm result from each primary spermatocyte that goes through meiosis.

Stem cells are deposited during gestation and are present at nascency through the beginning of boyhood just in an inactive country. During adolescence, gonadotropic hormones from the anterior pituitary cause the activation of these cells and the production of viable sperm. This continues into former age.

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 ane to ii million cells in the embryo.

Figure \(\PageIndex{7}\): Oogenesis The process of oogenesis occurs in the ovary's outermost layer. A primary oocyte begins the first meiotic partition but then arrests until afterward in life when information technology will finish this sectionalization in a developing follicle. This results in a secondary oocyte, which will complete meiosis if information technology is fertilized.

The prison cell starting meiosis is chosen a primary oocyte. This cell will brainstorm the beginning meiotic division, merely be arrested in its progress in the first prophase stage. At the time of nascency, all time to come eggs are in the prophase phase. At adolescence, inductive pituitary hormones cause the development of a number of follicles in an ovary. This results in the primary oocyte finishing the beginning meiotic division. The cell divides unequally, with most of the cellular cloth and organelles going to one cell, called a secondary oocyte, and only one set of chromosomes and a minor corporeality of cytoplasm going to the other prison cell. This 2d prison cell is called a polar torso and unremarkably 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. If the secondary oocyte is fertilized, the cell continues through the meiosis Ii, completing meiosis, producing a second polar body and a fertilized egg containing all 46 chromosomes of a man, half of them coming from the sperm.

Review

1. Explain how sexual reproduction occurs at the cellular level.
2. Summarize what happens during meiosis.
3. Compare and contrast gametogenesis in males and females.
4. Explain mechanisms that increase genetic variation in offspring produced past sexual reproduction.
5. Why do gametes need to be haploid? What would happen to the chromosome number later fertilization if they were diploid?
6. Describe one divergence between prophase I of meiosis and prophase of mitosis.
7. Do all of the chromosomes that yous got from your mother get into one of your gametes? Why or why not?
8. True or False . Crossing-over is the exchange of genetic fabric between sister chromatids.
9. True or False . Human sperms are haploid.
10. True or False . Sister chromatids separate from each other during meiosis I.
11. How many cells are produced after a single cell goes through meiosis?
12. Which stage of meiosis (prophase I or 2; metaphase I or 2; anaphase I or Two; telophase I or Two) all-time fits the descriptions beneath? Choose only 1 for each description.
    1. Pairs of homologous chromosomes line up along the equator of the cell
    2. Sister chromatids split up
    3. Homologous chromosomes separate from each other

Explore More

lyonsvaniffew.blogspot.com

Source: https://bio.libretexts.org/Bookshelves/Human_Biology/Book:_Human_Biology_%28Wakim_and_Grewal%29/07:_Cell_Reproduction/7.5:_Sexual_Reproduction:_Meiosis_and_gametogenesis

Share this post