1. MEIOSIS

2. Sexual Reproduction (two parents)
Meiosis
Sexual Reproduction (two parents)

4. What is the advantage of sexual reproduction?
Genetic Variation

5. 3 things that contribute to genetic variation
Independent assortment
Crossing Over
Random Fertilization
These two processes occur during meiosis

6. Why Meiosis?
Meiosis - cell division that halves the # of chromosomes when forming sex cells such as gametes or spores
Meiosis is the production of sex cells (gametes). During meiosis, the number of chromosomes in the daughter cells are reduced from the number of chromosomes in the parent cell (this is extremely important).

8. How does Meiosis Occur? Animation of meiosis to use as a review
Meiosis Animation from

9. Independent Assortment
Random arrangement of pairs of chromosomes

10. What is crossing over?
*Exchange of genetic material between homologous chromosomes
*Occurs during prophase I of meiosis.

11. Crossing Over
Crossing over often happens during meiosis. Have students notice that a segment of DNA has “crossed over” and exchanged with the other chromosome. This results in different combinations of genes for the offspring.

12. Crossing Over
Animation taken from

13. Is there anything that can wrong during meiosis?
Yes!
It is called nondisjunction.
Chromosomes don’t separate properly and some gametes end up with too many or not enough chromosomes.

14. What happens if nondisjunction occurs?
The gamete will die or result in conditions known as trisomy or monosomy.
Trisomy - a person has more than 2 copies of the same chromosome.
Monosomy – a person only has one copy of a chromosome.

15. How can you tell that? Take a picture of the chromosomes!
This is known as a karyotype.

16. Normal Female Karyotype

17. Normal Male Karyotype

18. Abnormal Karyotype-Trisomy #21
Down’s Syndrome

20. Abnormal Karyotype – Monosomy of the X chromosome
Turner’s Syndrome

21. Meiosis in males Called spermatogenesis Occurs in the testes
Results in 4 viable gametes called sperm

22. Meiosis in females Called oogenesis Occurs in the ovaries
Results in 1 viable gamete called the ovum (egg) and 3 polar bodies (these will die).
Why does only one gamete survive? The one egg will need a rich storehouse of nutrients to nourish the young organism that develops when the ovum is fertilized.

23. Meiosis Review
Is the beginning parent cell diploid or haploid (2n or n)? Diploid
2. Are the resulting daughter cells diploid or haploid (2n or n)? Haploid
Questions are animated so you can ask each question and get an answer before going to the next question.

24. More Meiosis Review 3. How many daughter cells are produced? 4
Are the resulting daughter cells different
from the
parent cell? yes

25. More Meiosis Review
5. Are the resulting daughter cells different from each other? yes
6. How many chromosomes are in a human parent cell? 46
Questions are animated so you can ask each question and get an answer before going to the next question.
7. How many chromosomes are in a human daughter cell? 23

26. More Meiosis Review
8. What types of cells are produced by meiosis?

27. Let’s review
Mitosis & Meiosis

28. Visual review of the differences between mitosis and meiosis

29. Mitosis vs. Meiosis √ √ √ √ √ √ Event Mitosis Meiosis Produces 4 cells
Mitosis vs. Meiosis
Event
Mitosis
Meiosis
Produces 4 cells
Produces 2 cells
New cells identical
New cells different
New cells have the same number of chromosomes as parent
New cells have fewer chromosomes than parent √ √ √ √
The answers are animated so you can have students answer the question before you reveal the answer. √ √

30. Mitosis vs. Meiosis √ √ √ √ √ Event Mitosis Meiosis
Mitosis vs. Meiosis
Event
Mitosis
Meiosis
Beginning cells diploid (2n)
Beginning cells haploid (n)
Ending cells diploid (2n)
Ending cells haploid (n)
Produces egg and sperm
Produces body cells (autosomes) √ √
The answers are animated so you can have students answer the question before you reveal the answer. √ √ √