1. Meiosis
Honors Biology
Spring 2013

2. Warm-Up With a neighbor, discuss the following: What is meiosis?
How does it differ from mitosis?

3. Essential Questions What is meiosis and why is it necessary?
What are the stages of meiosis?
How does meiosis compare to mitosis?

4. Haploid vs. Diploid Diploid cells 1. Body cells
2. Contains homologous chromosomes
3. 2N
B. Haploid cells
1. Sex cells
2. contains one member of each pair
3. 1N

5. Meiosis
Meiosis
process which reduces by half the number of chromosomes in a diploid cell
meiosis occurs in sex organs of individual

6. Overview of Meiosis A. Meiosis - formation of sex cells
1. Meiosis is cell division that results in a gamete containing half the number of chromosomes of its parent.
2. Meiosis includes 2 steps that each closely resemble corresponding steps in mitosis.

7. Phases of Meiosis meiosis I
Prophase I
Metaphase I
Anaphase I
Telophase I &?
Cytokinesis PMAT I
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II &?
Cytokinesis PMAT II

8. Meiosis 1 Meiosis I - reduction division 1. Interphase I 2. Prophase I
3. Metaphase I
4. Anaphase I
5. Telophase I

9. Meiosis 1: Prophase 1 chromatin condenses to form chromosomes
homologous chromosomes attach to form tetrads

10. Meiosis 1: Prophase 1 when tetrads form, crossing over can occur
crossing over is the
exchange of part of
homologous chromatids

11. Meiosis 1: Metaphase 1 tetrads line up on equator
spindle fibers attach to centromeres

12. Meiosis 1: Anaphase 1 homologous chromosomes separate
spindle fibers pull them
to opposite poles

13. Meiosis 1: Telophase and Cytokinesis
telophase I
nuclear membrane
reforms
cytokinesis
cytoplasm splits

14. Meiosis 1: Results results two haploid (n) daughter
cells = ½ the number of
chromosomes as parent cell

16. Meiosis II Meiosis II - separation of chromatids 1. Interphase II
2. Prophase II
3. Metaphase II
4. Anaphase II
5. Telophase II

17. Meiosis II: Prophase II
chromosomes already
formed

18. Meiosis II: Metaphase II
chromosomes line up
along equator

19. Meiosis II: Anaphase II
sister chromatids separate
move to opposite ends

20. Meiosis II: Telophase and Cytokinesis
telophase II
nuclear envelope reforms
cytokinesis
cytoplasm splits

21. Meiosis II: Results 4 haploid (n) daughter cells
all genetically different

22. Ploidy parent cell? dipliod (2n) after meiosis I?
haploid (n) (monopliod)
after meiosis II?
hapliod (n)

24. Purpose of Meiosis: Diversity
Meiosis and sexual reproduction significantly contribute to genetic variation among offspring.

25. Purpose of Meiosis: Gametes
role of meiosis is to produce gametes
meiosis in males
spermatogenesis
produces 4 sperm cells
meiosis in females
oogenesis
produces 1 ovum (egg cell) and 3 polar bodies

26. Where Does Meiosis Occur?

27. Mitosis vs. Meiosis where does is occur? number of cell divisions?
meiosis – sex organs; mitosis – somatic cells
number of cell divisions?
meiosis – 2; mitosis – 1
number of cells produced?
meiosis – 4; mitosis – 2
ploidy of daughter cells?
meiosis – hapliod (n); mitosis – dipliod (2n)
# of chromosomes compared to parent cell?
meiosis – ½ # chromosomes; mitosis – same

28. Mitosis vs. Meiosis