1. Review of Mitosis Four Phases
Asexual reproduction because daughter cells reproduced are identical to parent cell
Purpose is to replenish cells, assist in growth and development of an organism

2. Meiosis By the end of the lesson: I will be able to define meiosis
I will be able to define diploid & haploid
I will be able to define gamete
I will be able to identify the stages of
meiosis
I will be able to compare and contrast
mitosis and meiosis

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Meiosis Animation
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4. What is Meiosis?
A type of cell division that reduces the number of chromosomes
Reduces the chromosome number by half by splitting up pairs of chromosomes
A cell with 2n chromosomes will have n number of chromosomes after meiosis

5. Why go through the Trouble?
Each parent produces new combinations of genes through crossing over in gametes.
A single set of parents creates a unique combination of genes in a baby when they combine gametes.
This leads to new types of organisms with new adaptations.

6. Meiosis Overview 1. Involves 2 phases: Meiosis 1 and Meiosis 2
2. Results in 4 cells with 1/2 the normal genetic information.
3. Meiosis results in the formation of haploid sex cells called gametes.

7. Gametes These are the Ova (egg) and sperm.
Ova are produced in the ovaries in females (oogenesis)
Sperm are produced in the testes of males (spermatogenesis).

8. Spermatogenesis & Oogenesis

9. New Vocabulary Diploid (2N) - Normal amount of genetic material
Haploid (N) - 1/2 the genetic material.
Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote

10. Fertilization – “Putting it all together”
1n + 1n
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11. MEIOSIS I

12. Prophase 1 Prior to division, amount of DNA has doubled
Homologous Chromosomes are paired to form a tetrad.
Homologous chromosomes carry the same genes. One pair comes from the father and one from the mother
Homologous chromosomes
Tetrad

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Crossing-Over
Homologous chromosomes in a tetrad cross over each other
Pieces of chromosomes or genes are exchanged
Produces Genetic recombination in the offspring
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14. So why even go through the extra work?
Results in new genetic combinations or variation of offspring.
This is the main advantage of sexual reproduction

15. Why is it advantageous to have genetic variation in a population?

16. Homologous pairs of chromosomes align along the equator of the cell
Metaphase I
Homologous pairs of chromosomes align along the equator of the cell
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*Anaphase I
Homologous chromosomes separate and move to opposite poles.
Sister chromatids remain
attached at their centromeres.
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Telophase I
Nuclear envelopes reassemble.
Spindle disappears.
Cytokinesis divides cell into two.
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19. MEIOSIS II

20. Meiosis II DNA does not double  IT IS REDUCED from diploid to haploid
The rest of meiosis II is similar to mitosis

21. Meiosis II: Reducing Chromosome Number
Prophase II
Metaphase II
Telophase II
Anaphase II
4 Genetically Different haploid cells
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22. Meiosis
The most important thing to remember in distinguishing Mitosis from Meiosis is:
Mitosis
Meiosis
body cells (somatic cells)
sex cells (Gametes)
results in 2 genetically identical diploid cells.
produces 4 genetically different haploid cells.
1 round
2 rounds

23. Humans
Every organism must inherit a single copy of every gene from both its parents. With us, we get 23 from our mom and 23 from our dad. 46 total.
So when you produce your own gametes (sex cells) these 2 sets of genes have to be separated from each other so that each gamete contains just one set of genes.

24. Meiosis 1 diploid parent cell divides into 4 haploid daughter cells
(for reproduction).
Meiosis forms sperm or eggs
called gametes that are haploid.
Each parent donates 1 set of 23
chromosomes to the child
(46 total for the baby).