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Meiosis

Meiosis. Meiosis. Meiosis. Meiosis. Meiosis. Meiosis. Meiosis. Sumana Veeravelli Nicole Quincy Janet Kim P.5 10/10/06. Meiosis. Meiosis. Meiosis. Meiosis. Meiosis. Meiosis. Meiosis. Overview of Meiosis. What is Meiosis?

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Meiosis

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  1. Meiosis Meiosis Meiosis Meiosis Meiosis Meiosis Meiosis Sumana Veeravelli Nicole Quincy Janet Kim P.5 10/10/06 Meiosis Meiosis Meiosis Meiosis Meiosis Meiosis Meiosis

  2. Overview of Meiosis What is Meiosis? Meiosis is a cell division process that results in the formation of sex cells. -gametes in animals -spores in plants Meiosis involves two divisions producing a total of four daughter cells. Summary of the Phases of Meiosis A cell undergoing meiosis will divide two times; the first division is meiosis 1 and the second is meiosis 2. Each has four phases which will be covered in this presentation. meiosis 1: prophase 1, metaphase 1, anaphase 1, and telophase 1 meiosis 2: prophase 2, metaphase 2, anaphase 2, and telophase 2

  3. Location and Purpose of Meiosis Location: Meiosis only occurs in sexually reproducing organisms such as eukaryotic plant and animal diploid cells. Diploid cells are cells which have two sets of chromosomes. Purpose: The purpose of meiosis to reduce the normal diploid cells (2n) to haploid cells(n), “n” being the chromosome number.

  4. Meiosis I Phases Prophase I: • Already copied chromosomes start to thicken and shorten. • Chromosomes pair together. • Crossing-over occurs. • Two homologous pairs join together to form tetrads. • Nucleolus disappears. • Meiotic spindle forms between two pairs of centrioles. • Spindle enters nucleus.

  5. Meiosis I Phases cont. Metaphase I: • Centrioles at opposite poles of cell. • Tetrads become situated on metaphase plate. • Spindle fibers from one pole attach to one chromosome of each pair; spindle fibers from other pole attach to other chromosomes. Metaphase Plate Meiotic Spindle

  6. Meiosis I Phases cont. Anaphase I: • Two chromosomes of each tetrad separate, move toward opposite poles. • Note: Sister chromatids remain attached at centromeres, move together toward poles.

  7. Meiosis I Phases cont. Telophase I: • Homologous chromosome pairs complete migration to poles; now haploid set of chromosomes at each pole. • Nuclear envelope forms around each chromosome set. • Spindle disappears. • Cytokinesis occurs.

  8. Meiosis II Begins with the two sister cells formed in Meiosis I • The four phases of Meiosis II are: 1. Prophase 2 2. Metaphase 2 3. Anaphase2 4. Telophase2 The results are four haploid daughter cells, each with half the chromosomes as the original diploid cell

  9. Step 1: Prophase 2 - Begins without duplicating DNA. -Nucleolus and nuclear envelope disappear -Centriole duplicates and they move to opposite poles of the cell Step 2: Metaphase 2 -The spindle fibers from the centrioles attach to the chromosomes - Chromosomes line up on the equatorial plate.

  10. Step 3: Anaphase 2 - Centromeres divide and separated sister chromatids move to each pole. Step 4: Telophase 2 - Four haploid daughter cells are produced, and cell division is complete.

  11. What is special about the end product? • The daughter cells are genetically different from the parent cell, and have halfthe number of chromosomes.

  12. Review of Meiosis Meiosis I consists of: Prophase 1 • Nucleolus disappears, and meiotic spindle forms between 2 centrioles • Nuclear envelope disappears, meiotic spindle enters Gamete Before Meiosis Metaphase1 • Centrioles move to opposite poles of cell • The chromosomes are arranged on the metaphase plate • Spindle fibers from each pole attach to a chromosome from each pair of sister chromatids Anaphase 1 Sister Cells formed from Meiosis I • Chromosomes of each bivalent separate and are pulled by the spindle to opposite poles Telophase 1 • The chromosomes continue to move until there is a haploid set of chromosomes at each pole • A nuclear envelope forms around each chromosome set • The spindle disappears and cytokinesis follows

  13. Review of Meiosis, cont. Meiosis II consists of: Prophase 2 • Nucleolus disappears and meiotic spindle forms between 2 centrioles • The nuclear envelope disappears and the spindle apparatus forms Metaphase 2 Four Haploid Daughter Cells formed from Meiosis II • Centrioles move to opposite poles of cell • Chromosomes are arranged on the metaphase plate Anaphase 2 • Centromeres are pulled apart • Separated chromatids are moved to opposite poles of the cell by the meiotic spindle Telophase 2 • Nuclear envelope forms around chromosomes • Cytokinesis produces four daughter cells, each having a set of haploid chromosomes

  14. WORKS CITED "BioCoach Activity." Meiosis. 2006. Pearson Education, Inc.. 11 Oct 2006 <http://www.phschool.com/science/biology_place/biocoach/mei osis/teloii.html>. Carter, J. Stein. "Meiosis." Meiosis. 02 Nov. 2004. Sci Links. 11 Oct 2006 <http://biology.clc.uc.edu/courses/bio104/meiosis.htm>. Foster, Gerry. "Section 3: Cells and the Cell Cycle - Part c." Meiosis. 2006. 11 Oct 2006 <http://www.dvbiology.org/biologyweb/bcell2.htm#part%20d>. "The Biology Project: Cell Biology." Meiosis I & II. Aug. 2004. Department of Biochemistry and Molecular Biophysics . 11 Oct 2006 <http://www.biology.arizona.edu/cell_bio/tutorials/meiosis/page3. html>.

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