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
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. The four phases of Meiosis II are:
Begins with the two sister cells formed in Meiosis I
The four phases of Meiosis II are:
1. Prophase Metaphase Anaphase 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 half the number of chromosomes.

12. Review of Meiosis Meiosis I consists of: Gamete Before Meiosis
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. Meiosis II consists of: Four Haploid Daughter Cells
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 Pearson Education, Inc.. 11 Oct < osis/teloii.html>.
Carter, J. Stein. "Meiosis." Meiosis. 02 Nov Sci Links. 11 Oct <
Foster, Gerry. "Section 3: Cells and the Cell Cycle - Part c." Meiosis Oct <
"The Biology Project: Cell Biology." Meiosis I & II. Aug Department of Biochemistry and Molecular Biophysics . 11 Oct < html>.

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