1. MEIOSIS
Hey there good lookin’

2. Human Chromosomes-23 Pairs 1/2 from mom, 1/2 from dad

3. Meiosis…in a nut shell
-Cell division resulting in the creation of four gamete cells from a single reproductive cell.

5. STEPS TO MEIOSIS Meiosis I Meiosis II
Prophase I, Metaphase I, Anaphase I, Telophase I
Meiosis II
Prophase II, Metaphase II, Anaphase II, Telophase II

6. Haploid vs. Diploid Haploid-1n Diploid-2n
one of each type of chromosomes
Diploid-2n
two of each type of chromosomes

7. HAPLOID- 1N 1 of each type of chromosome
UNDUPLICATED
DUPLICATED

8. DIPLOID-2N 2 of each type of chromosome
UNDUPLICATED
DUPLICATED

9. Meiosis… -Resulting gametes have half the number of
chromosomes (haploid.)
-Example: one human reproductive cell with 46 chromosomes (diploid) is split into four gamete cells each with 23 chromosomes (haploid).
-Why is it important for sex cells to be haploid??

10. Key Events of Meiosis:
Interphase precedes Meiosis…’S’ Phase is required for replication of genetic material (DNA).
Crossing Over of Homologous Pairs (Prophase I)
Genetic Variation
Independent Assortment (Metaphase I into Anaphase I)
Lining up of the chromosomes during Metaphase I & II
Splitting of chromosomes during Anaphase I & II
Why is it important for gametes to have genetic variation?

11. Interphase DNA is in the form of chromatin
S-phase…replication of genetic material (DNA)

12. Prophase I Nuclear envelope breaks down Homologous chromosomes pair up
A pair of homologous chromosomes is called a tetrad.
Crossing-over occurs resulting in genetic recombination leading to variation.

13. Metaphase I
Look at the arrangement of chromosomes…they are lined up in homologous pairs at the equator.
Random lining up of chromosomes during Metaphase I is part of the process of independent assortment.

14. Mitosis Metaphase vs. Meiosis Metaphase I

15. Anaphase I
The separation of homologous pairs is also part of independent assortment.
This results in genetic variation!

16. Mitosis Anaphase vs. Meiosis Anaphase I

17. Telophase I
Two genetically diverse cells are created, each with 23 replicated chromosomes (haploid).

18. Prophase II
Prophase II begins with two haploid cells each containing 23 replicated chromosomes.

19. Metaphase II

20. Anaphase II
In anaphase II, the 23 replicated chromosomes separate into 23 sister chromatids.

21. Telophase II
The result of telophase II is four unique haploid cells each with 23 chromosomes.

26. What is the final result?
We end up with 4 haploid sex cells that came from one original diploid cell.
Why do we need this to occur?
-One cell with 23 chromosomes (sperm) + one cell with 23 chromosomes (egg) = one cell with 46 chromosomes!
-Meiosis creates genetic diversity which allows variation in the offspring of sexual reproduction. This variation allows species to adapt rapidly to new conditions for survival.

27. Meiosis Videos