explain breifly the process of cell division in animals
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Cells can divide by either mitosis ormeiosis. Both of these are preceeded by the interphase.
Interphase consists of three stages: the G1stage, the S stage, and the G2 stage. During the G1 phase all the internal organelles of the animal cell are replicated, during the S phase (the longest phase) all the DNA of the cell is replicated, and during the G2 phase the replicated DNA is checked for mutations. This process is necessary prior to mitosis to ensure that the cell has twice the usual amount of organelles and twice the usual amount of DNA to ensure that two genetically identical diploid cells can be produced when the cell divides by equatoral division in mitosis.
Mitosis consists of prophase, metaphase, anaphase, and telophase, followed bycytokinesis.
During prophase, the nucleolus disappears, the nuclear envelope breaks down (dissociates completely),membranous organelles scatter towards the periphery of the cell, the chromatincontinues to condense so each replicated homologous chromosome in a pair becomes visible as two sister chromatidsjoined at the centromere (each of a pair of homologous chromosomes, one paternal and one maternal, that contain the same amount and sequence of DNA/same genes but may have different alleles and are not functionally equivalent, is replicated in interphase and consists of two identical sister chromatids), the microtubulesform a 3D structure called the spindle,and centrioles move to opposite ends/poles of the cell and organise the spindle into spindle fibers. Finally, replicated homologous chromosomes move towards the equator of the cell and spindle fibers start extending towards the equator of the cell.
During metaphase, the replicated DNA lines up in single file along the equator of the cell and spindle fibers attach to the chromosomes at the centromere.
During anaphase the spindle fibers shorten, pulling the two sister chromatids of each replicated homologous chromosome towardsopposite ends of the cell. Therefore sister chromatids, now referred to as chromosomes, are pulled to opposite poles (centrioles) of the cell.
Telophase is the opposite of prophase; two new nuclear envelopes start to reform, and two nucleoli reappear. Replicatedmembranous organelles arrange themselves in the correct position in two separate areas of the cell, as the cell expands giving it a stretched look (two new cells start to become visible), thechromatin unravels into thin strands of DNA, the spindle fibers break down, and the centrioles move away from the poles of the cell.
The last stage is cytokinesis, which is thesplitting of the cell membrane to form two new cells after the cytoplasm divides. In plant cells this is done by synthesising a new cell plate in between the two nuclei, which becomes a part of the new cell wall of each genetically identical daughter cell as the cytoplasm divides and the two cells split.
The cell cycle (interphase) and mitosis are vital in both plant and animal cells as they allow growth and repair and asexual reproduction to occur.
Meiosis occurs in the sex organs. Gametes form when primordial germ cells (the cells of the ovaries or testicles) divide by meiosis to form mature germ cells(gametes). The parent cell undergoes two divisions. In the first meiotic divisionreduction division occurs as homologous pairs of replicated chromosomes line up next to each other on the equator of the cell, thus when the cell divides the ploidy level is reduced from 2 to 1 (as each daughter cell only contains one set of chromosomes/one of each homologous pair). During this division independent assortment occurs (the random lining up of homologous pairs of replicated chromosomes on the equator before reduction division, meaning that each daughter cell has a unique combination of maternal and paternal chromosomes) andcrossing over occurs (the swapping of sections of homologous chromosomes at chiasmata, therefore some alleles are transferred from one chromosome to another creating a unique combination of alleles in daughter cells) to create genetic variation in the gametes.
The gametes form to fulfill the purpose of meiosis: the mixing of genetic materialvia the combination of a haploid maternal gamete and a haploid paternal gamete infertilisation (as the haploid pronuclei fuse) to form a totipotent diploid zygote(with the right number of chromosomes, ploidy level = 2) that is genetically different to the parent cells, therefore conserving genetic diversity (through genetic variation in the gametes).
Interphase consists of three stages: the G1stage, the S stage, and the G2 stage. During the G1 phase all the internal organelles of the animal cell are replicated, during the S phase (the longest phase) all the DNA of the cell is replicated, and during the G2 phase the replicated DNA is checked for mutations. This process is necessary prior to mitosis to ensure that the cell has twice the usual amount of organelles and twice the usual amount of DNA to ensure that two genetically identical diploid cells can be produced when the cell divides by equatoral division in mitosis.
Mitosis consists of prophase, metaphase, anaphase, and telophase, followed bycytokinesis.
During prophase, the nucleolus disappears, the nuclear envelope breaks down (dissociates completely),membranous organelles scatter towards the periphery of the cell, the chromatincontinues to condense so each replicated homologous chromosome in a pair becomes visible as two sister chromatidsjoined at the centromere (each of a pair of homologous chromosomes, one paternal and one maternal, that contain the same amount and sequence of DNA/same genes but may have different alleles and are not functionally equivalent, is replicated in interphase and consists of two identical sister chromatids), the microtubulesform a 3D structure called the spindle,and centrioles move to opposite ends/poles of the cell and organise the spindle into spindle fibers. Finally, replicated homologous chromosomes move towards the equator of the cell and spindle fibers start extending towards the equator of the cell.
During metaphase, the replicated DNA lines up in single file along the equator of the cell and spindle fibers attach to the chromosomes at the centromere.
During anaphase the spindle fibers shorten, pulling the two sister chromatids of each replicated homologous chromosome towardsopposite ends of the cell. Therefore sister chromatids, now referred to as chromosomes, are pulled to opposite poles (centrioles) of the cell.
Telophase is the opposite of prophase; two new nuclear envelopes start to reform, and two nucleoli reappear. Replicatedmembranous organelles arrange themselves in the correct position in two separate areas of the cell, as the cell expands giving it a stretched look (two new cells start to become visible), thechromatin unravels into thin strands of DNA, the spindle fibers break down, and the centrioles move away from the poles of the cell.
The last stage is cytokinesis, which is thesplitting of the cell membrane to form two new cells after the cytoplasm divides. In plant cells this is done by synthesising a new cell plate in between the two nuclei, which becomes a part of the new cell wall of each genetically identical daughter cell as the cytoplasm divides and the two cells split.
The cell cycle (interphase) and mitosis are vital in both plant and animal cells as they allow growth and repair and asexual reproduction to occur.
Meiosis occurs in the sex organs. Gametes form when primordial germ cells (the cells of the ovaries or testicles) divide by meiosis to form mature germ cells(gametes). The parent cell undergoes two divisions. In the first meiotic divisionreduction division occurs as homologous pairs of replicated chromosomes line up next to each other on the equator of the cell, thus when the cell divides the ploidy level is reduced from 2 to 1 (as each daughter cell only contains one set of chromosomes/one of each homologous pair). During this division independent assortment occurs (the random lining up of homologous pairs of replicated chromosomes on the equator before reduction division, meaning that each daughter cell has a unique combination of maternal and paternal chromosomes) andcrossing over occurs (the swapping of sections of homologous chromosomes at chiasmata, therefore some alleles are transferred from one chromosome to another creating a unique combination of alleles in daughter cells) to create genetic variation in the gametes.
The gametes form to fulfill the purpose of meiosis: the mixing of genetic materialvia the combination of a haploid maternal gamete and a haploid paternal gamete infertilisation (as the haploid pronuclei fuse) to form a totipotent diploid zygote(with the right number of chromosomes, ploidy level = 2) that is genetically different to the parent cells, therefore conserving genetic diversity (through genetic variation in the gametes).
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☜☆☞ Mitosis is a cell division that occurs in animal cells where each mother cell divides into 2 daughter cells. The number of chromosomes in the mother cell is identical to that in each resulting daughter cell. This is why mitosis is sometimes called an ” Identical Reproduction of Cells”. It occurs in the somatic cells and it is meant for the multiplication of cell number during embryogenesis and blastogenesis of plants and animals.
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☜☆☞ Mitosis is a cell division that occurs in animal cells where each mother cell divides into 2 daughter cells. The number of chromosomes in the mother cell is identical to that in each resulting daughter cell. This is why mitosis is sometimes called an ” Identical Reproduction of Cells”. It occurs in the somatic cells and it is meant for the multiplication of cell number during embryogenesis and blastogenesis of plants and animals.
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