1. Meiosis

2. Now that you know all about DNA….
How is DNA passed from parent to offspring?
There are two main ways that DNA is passed from parent to offspring:
1. Asexual reproduction – process by which a single parent reproduces by itself
Mitosis is a form of asexual reproduction.
In this process, the parent and offspring will be genetically identical.
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3. 2. Sexual reproduction – process by which two cells from different parents unite to produce the first cell of the new offspring
Meiosis is the process used to create genetically different gametes (sperm/eggs) used in sexual reproduction.
In this process, the parents and offspring will be genetically unique.
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4. What is meiosis?
Meiosis is a type of cell division that results in four genetically different haploid cells.
Diploid (2N) – a cell with ‘2 sets’ of chromosomes
Haploid (1N) – a cell with ‘1 set’ of chromosomes
Meiosis is used to produce haploid gametes (sperm and eggs) in organisms that reproduce sexually.
Human gametes:
In men, meiosis produces 4 equally sized sperm cells.
In women, meiosis produces 1 egg and 3 polar bodies that later disintegrate.

5. The Phases of Meiosis
The phases of meiosis are the same as the phases of mitosis, but in meiosis each phase occurs twice.
Meiosis I includes, Prophase I, Metaphase I, Anaphase I, and Telophase I, followed by Cytokinesis.
Meiosis I results in 2 haploid daughter cells.

6. Meiosis I
In prophase I, homologous chromosomes pair up and form a tetrad.
Homologous chromosomes – Refers to two similar chromosomes in a diploid cell. One chromosome is derived from the father gamete cell and the other from the mother
Crossing over – homologous chromosomes exchange pieces of DNA to produce genetically different gametes.

7. A Sketch of Chromosomes Crossing Over (Prophase I)
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8. Meiosis II
Includes Prophase II, Metaphase II, Anaphase II, and Telophase II, followed by Cytokinesis.
Each of the haploid daughter cells from meiosis I divide again to make 4 haploid cells.

9. Comparing Mitosis and Meiosis
The processes of mitosis and meiosis are very similar, but with some important differences:
Mitosis
Includes only 1 cycle of cell division
Occurs in body cells
No crossing over of chromosomes
Results in two genetically identical diploid cells
Metaphase: 1 duplicated chromosome per spindle fiber
Meiosis
Includes 2 cycles of cell division (meiosis I and meiosis II)
Occurs only in gametes (sex cells)
Chromosomes cross over in Prophase I
Results in four genetically different haploid cells
Metaphase I: 2 duplicated chromosomes per spindle fiber

10. Now, let’s look at our flipbook and compare!!

11. Interphase DNA replication occurs.
DNA is in an uncondensed form known as chromatin.

12. Prophase I DNA condenses to form chromosomes.
Homologous chromosomes pair up to form a tetrad.
Crossing over occurs.

13. Metaphase I Homologous pairs line up along center of cell
1 homologous chromosome and its duplicate are attached to each spindle fiber

14. Anaphase I
Homologous pairs are separated, move to opposite ends of the cell.

15. Telophase I
Nuclear membrane will reappear.
Spindle fibers disappear.

16. Cytokinesis Cytoplasm of the two cells separate.
Meiosis I results in 2 haploid cells that are genetically different.

17. Prophase II
The 2 haploid cells from Meiosis I will divide again.

18. Metaphase II
Chromosomes (set of sister chromatids) line up along the center of the cell.
1 sister chromatid is attached to each spindle fiber.

19. Anaphase II
Centromeres split and sister chromatids are pulled apart.

20. Telophase II and Cytokinesis
The cytoplasmic division occurs, resulting in 4 genetically different haploid cells.