Learning Objectives
The Cell Division Cycle Show
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Cell division cycle, figure from Wikipedia. Cells that stop dividing exit the G1 phase of the cell cycle into a so-called G0 state. Cells 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:
ChromosomesChromosomes 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. 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. Human karyotype “painted” using fluorescent DNA probes. These mitotic chromosomes each consist of a pair of sister chromatids joined at their centromeres. The images of the homologous chromosome pairs (e.g., 2 copies of chromosome 1) have been lined up next to each other. Image from Bolzer et al., (2005) Three-Dimensional Maps of All Chromosomes in Human Male Fibroblast Nuclei and Prometaphase Rosettes. PLoS Biol 3(5): e157 DOI: 10.1371/journal.pbio.0030157 Ploidy
Here is a simplified diagram illustrating the overall process and products of mitosis: Source: Wikimedia Commons (https://commons.wikimedia.org/wiki/File:MajorEventsInMeiosis_variant_int.svg) Questions or points to ponder or note about the figure above (answers at bottom of page):
This animation below shows the packaging of DNA and condensation of chromosomes as a cell
undergoes mitosis. MeiosisThis 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.
The last point appears to be the most difficult for students to grasp. Consider
the X and Y chromosomes. They pair in prophase I, and then separate in the first division. The daughter cells of the first meiotic division have either an X or a Y; they don’t have both. Each cell now has only one sex chromosome, like a haploid cell. Meiosis Overview from Wikipedia by Rdbickel And here is a video that walks through the steps of meiosis:
Chromosomes, chromatids, what is the difference and how many chromosomes are there at different times of the cell cycle and after mitosis and meiosis?Chromosomes by definition contain the DNA that makes up the fundamental genome of the cell. In a prokaryote, the genome is usually packaged into one circular chromosome consisting of a
circular DNA molecule of a few million base pairs (Mbp). In eukaryotes, the genome is packaged into multiple linear chromosomes, each consisting of a linear DNA molecule of tens or hundreds of Mbp. Chromosomes exist at all different phases of the cell cycle. They condense and become visible to light microscopy in prophase of mitosis or meiosis, and they decondense during interphase, in the form of chromatin (DNA wrapped around nucleosomes, like “beads on a string”). Meiosis Overview from Wikipedia by Rdbickel The video below is geared toward a high school audience, but it does present a helpful way for recognizing how many chromosomes are present in a cell (and thus the ploidy level of that cell). While watching, see if you can recognize why the products of meiosis 1 are haploid cells: Answers to questions about the mitosis figure:
Which of the following correctly describes how mitosis and meiosis are similar?Which of the following correctly describes how mitosis and meiosis are similar? Sister chromatids segregate to opposite poles of the cell during both mitosis and meiosis. What are the similarities between meiosis 1 and mitosis?Both mitosis and meiosis involve cell division. Both the processes occur in the M-phase of the cell cycle. In both cycles, the typical stages are prophase, metaphase, anaphase and telophase. In both cycles, synthesis of DNA takes place. In what way is mitosis similar to meiosis quizlet?The fundamental sequence of events in mitosis is the same as in meiosis (in meiosis it happens twice). Both processes include the breakdown of the nuclear membrane, the separation of genetic material into two groups, followed by cell division and the reformation of the nuclear membrane in each cells. Which correctly describes mitosis and meiosis?Which correctly describes mitosis and meiosis? Mitosis creates genetically identical cells, whereas meiosis creates genetically unique cells. What is the difference between meiosis 1 and meiosis 2?There are two divisions in meiosis; the first division is meiosis I: the number of cells is doubled but the number of chromosomes is not. This results in 1/2 as many chromosomes per cell. The second division is meiosis II: this division is like mitosis; the number of chromosomes does not get reduced.
What is the difference between meiosis 1 and meiosis 2 quizlet?Meiosis I is a reduction division where only one member of a homologous pair enters each daughter cell which becomes halploid. Meiosis II only splits up sister chromatids. Sister chromatids are not pulled apart in meiosis I at the centromere like in mitosis but are in meiosis II.
How is mitosis 1 and meiosis 2 different?The main difference between meiosis II and mitosis is that the meiosis II essentially occurs in haploid cells that have gone through meiosis I whereas the mitosis mainly occurs in diploid cells. Moreover, meiosis II occurs in the production of gametes in sexual reproduction while mitosis occurs in asexual reproduction.
Which of the following correctly describes how mitosis and meiosis are different choose 1 answer?D. Correct - Cells produced through mitosis contain DNA identical to the parent cells, whereas meiosis produces cells that are haploid and often genetically different. Bio.
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