MITOSIS, MEIOSIS AND THE CELL CYCLE
1.6 هزار بار بازدید -
6 سال پیش
-
Mitosis is a form of
Mitosis is a form of eukaryotic cell division that produces two daughter cells with the same genetic component as the parent cell. Chromosomes replicated during the S phase are divided in such a way as to ensure that each daughter cell receives a copy of every chromosome. ells reproduce genetically identical copies of themselves by cycles of cell growth and division. The cell cycle diagram on the left shows that a cell division cycle consists of 4 stages:
G1 is the period after cell division, and before the start of DNA replication. Cells grow and monitor their environment to determine whether they should initiate another round of cell division.
S is the period of DNA synthesis, where cells replicate their chromosomes.
G2 is the period between the end of DNA replication and the start of cell division. Cells check to make sure DNA replication has successfully completed, and make any necessary repairs.
M is the actual period of cell division, consisting of prophase, metaphase, anaphase, telophase, and cytokinesis.Chromosomes were first named by cytologists viewing dividing cells through a microscope. The modern definition of a chromosome now includes the function of heredity and the chemical composition. A chromosome is a DNA molecule that carries all or part of the hereditary information of an organism. In eukaryotic cells, the DNA is packaged with proteins in the nucleus, and varies in structure and appearance at different parts of the cell cycle.
Chromosomes condense and become visible by light microscopy as eukaryotic cells enter mitosis or meiosis. During interphase (G1 + S + G2), chromosomes are fully or partially decondensed, in the form of chromatin, which consists of DNA wound around histone proteins (nucleosomes).In G1, each chromosome is a single chromatid. In G2, after DNA replication in S phase, as cell enter mitotic prophase, each chromosome consists of a pair of identical sister chromatids, where each chromatid contains a linear DNA molecule that is identical to the joined sister. The sister chromatids are joined at their centromeres, as shown in the image below. A pair of sister chromatids is a single replicated chromosome, a single package of hereditary information. Mitosis produces two daughter cells that are genetically identical to each other, and to the parental cell. A diploid cell starts with 2N chromosomes and 2X DNA content. After DNA replication, the cells is still genetically diploid (2N chromosome number), but has 4X DNA content because each chromosome has replicated its DNA. Each chromosome now consists of a joined pair of identical sister chromatids. During mitosis the sister chromatids separate and go to opposite ends of the dividing cell. Mitosis ends with 2 identical cells, each with 2N chromosomes and 2X DNA content. All eukaryotic cells replicate via mitosis, except germline cells that undergo meiosis (see below) to produce gametes (eggs and sperm).
prophase – chromosomes condense; each chromosome consists of a pair of identical sister chromatids joined at the centromere.
metaphase – chromosomes line up at the middle of the cell, along the plane of cell division, pushed and pulled by microtubules of the spindle apparatus
anaphase – sister chromatids separate and migrate towards opposite ends of the cell
telophase – chromatids cluster at opposite ends of the cell and begin to decondense
cytokinesis – the membrane pinches in to divide the two daughter cells Meiosis
This is a special sequence of 2 cell divisions that produces haploid gametes from diploid germline cells. It starts with a diploid cell that has undergone chromosomal DNA replication: 2N chromosomes, 4X DNA content. Two successive divisions, with no additional DNA replication, results in 4 haploid gametes: 1N chromosomes, 1X DNA content.
NOVA has a good interactive side-by-side comparison of mitosis and meiosis on this page: How cells divide
Meiosis sets the stage for Mendelian genetics. Students need to know that most of the genetics action occurs in the first meiotic division:
homologous chromosomes pair up and align end-to-end (synapsis) in prophase I
crossing over occurs between homologous chromosomes in prophase I, before chromosomes line up at the metaphase plate
homologous chromosomes separate to daughter cells (sister chromatids do not separate) in the first division, creating haploid (1N) cells
the separation of each pair of homologous chromosomes occurs independently, so all possible combinations of maternal and paternal chromosomes are possible in the two daughter cells – this is the basis of Mendel’s Law of Independent Assortment
the first division is when daughter cells become functionally or genetically haploid Ploidy
Humans are diploid, meaning we have two copies of each chromosome. We inherited one copy of each chromosome from other mother, and one copy of each from our father. Gametes (sperm cells or egg cells) are haploid, meaning that they have just one complete set of chromosomes
G1 is the period after cell division, and before the start of DNA replication. Cells grow and monitor their environment to determine whether they should initiate another round of cell division.
S is the period of DNA synthesis, where cells replicate their chromosomes.
G2 is the period between the end of DNA replication and the start of cell division. Cells check to make sure DNA replication has successfully completed, and make any necessary repairs.
M is the actual period of cell division, consisting of prophase, metaphase, anaphase, telophase, and cytokinesis.Chromosomes were first named by cytologists viewing dividing cells through a microscope. The modern definition of a chromosome now includes the function of heredity and the chemical composition. A chromosome is a DNA molecule that carries all or part of the hereditary information of an organism. In eukaryotic cells, the DNA is packaged with proteins in the nucleus, and varies in structure and appearance at different parts of the cell cycle.
Chromosomes condense and become visible by light microscopy as eukaryotic cells enter mitosis or meiosis. During interphase (G1 + S + G2), chromosomes are fully or partially decondensed, in the form of chromatin, which consists of DNA wound around histone proteins (nucleosomes).In G1, each chromosome is a single chromatid. In G2, after DNA replication in S phase, as cell enter mitotic prophase, each chromosome consists of a pair of identical sister chromatids, where each chromatid contains a linear DNA molecule that is identical to the joined sister. The sister chromatids are joined at their centromeres, as shown in the image below. A pair of sister chromatids is a single replicated chromosome, a single package of hereditary information. Mitosis produces two daughter cells that are genetically identical to each other, and to the parental cell. A diploid cell starts with 2N chromosomes and 2X DNA content. After DNA replication, the cells is still genetically diploid (2N chromosome number), but has 4X DNA content because each chromosome has replicated its DNA. Each chromosome now consists of a joined pair of identical sister chromatids. During mitosis the sister chromatids separate and go to opposite ends of the dividing cell. Mitosis ends with 2 identical cells, each with 2N chromosomes and 2X DNA content. All eukaryotic cells replicate via mitosis, except germline cells that undergo meiosis (see below) to produce gametes (eggs and sperm).
prophase – chromosomes condense; each chromosome consists of a pair of identical sister chromatids joined at the centromere.
metaphase – chromosomes line up at the middle of the cell, along the plane of cell division, pushed and pulled by microtubules of the spindle apparatus
anaphase – sister chromatids separate and migrate towards opposite ends of the cell
telophase – chromatids cluster at opposite ends of the cell and begin to decondense
cytokinesis – the membrane pinches in to divide the two daughter cells Meiosis
This is a special sequence of 2 cell divisions that produces haploid gametes from diploid germline cells. It starts with a diploid cell that has undergone chromosomal DNA replication: 2N chromosomes, 4X DNA content. Two successive divisions, with no additional DNA replication, results in 4 haploid gametes: 1N chromosomes, 1X DNA content.
NOVA has a good interactive side-by-side comparison of mitosis and meiosis on this page: How cells divide
Meiosis sets the stage for Mendelian genetics. Students need to know that most of the genetics action occurs in the first meiotic division:
homologous chromosomes pair up and align end-to-end (synapsis) in prophase I
crossing over occurs between homologous chromosomes in prophase I, before chromosomes line up at the metaphase plate
homologous chromosomes separate to daughter cells (sister chromatids do not separate) in the first division, creating haploid (1N) cells
the separation of each pair of homologous chromosomes occurs independently, so all possible combinations of maternal and paternal chromosomes are possible in the two daughter cells – this is the basis of Mendel’s Law of Independent Assortment
the first division is when daughter cells become functionally or genetically haploid Ploidy
Humans are diploid, meaning we have two copies of each chromosome. We inherited one copy of each chromosome from other mother, and one copy of each from our father. Gametes (sperm cells or egg cells) are haploid, meaning that they have just one complete set of chromosomes
6 سال پیش
در تاریخ 1397/03/29 منتشر شده
است.
1,698
بـار بازدید شده