1. 11.4 Meiosis
KEY CONCEPT During meiosis, diploid cells undergo two cell divisions that result in haploid cells.

2. Cells go through two rounds of division in meiosis.
Meiosis I (first division) and Meiosis II (second division)
occurs in gametes (sperm and egg)
diploid  haploid (2n  1n)
creates genetic diversity (variations)
Diploid
Meiosis I
Meiosis II
Haploid

3. 11.4 Meiosis
Meiosis I and meiosis II each have four phases, similar to those in mitosis
Interphase  Meiosis 1 (P1-M1-A1-T1-Cytokinesis)
 Meiosis 2 (P2-M2-A2-T2-Cytoknesis)
Pairs of homologous chromosomes separate in meiosis I.
Sister chromatids divide in meiosis II.
homologous chromosomes
sister
chromatids
sister
chromatids

4. 11.4 Meiosis
Meiosis I occurs after DNA has been replicated (interphase).
Meiosis I divides homologous chromosomes in four phases.

5. 11.4 Meiosis
Prophase I
- similar to Prophase in mitosis except homologous
chromosomes pair up (one from Dad and one from Mom)

6. 11.4 Meiosis
Prophase I
- When homologous chromosomes pair up, crossing over
may occur.
- Crossing over is the exchange of DNA between two
homologous chromosome.
- Crossing over results in genetic variations. (this is why
siblings may look similar, but still different)

7. 11.4 Meiosis How does meiosis explain family resemblance and
differences………….
Let’s look at some Celebrity Brothers and Sisters !!

8. 11.4 Meiosis Metaphase 1, Anaphase 1, Telophase 1, Cytokinesis
- homologous chromosomes line up, split up, divide into two
cells, and ready to proceed to Meiosis 2

9. 11.4 Meiosis Meiosis II divides sister chromatids in four phases.
DNA is not replicated between Meiosis I and Meiosis II.
Two cells divide into four haploid cells.

10. Haploid cells develop into mature gametes.
11.4 Meiosis
Haploid cells develop into mature gametes.
Gametogenesis is the production of gametes.
Gametogenesis differs between females and males.
Spermatogenesis = sperm production
1 germ cell  4 sperm cells
Oogenesis = egg production
1 germ cell 
1 egg cell + 3 polar bodies

11. 11.4 Meiosis
Meiosis differs from mitosis in significant ways.

12. Comparing Mitosis and Meiosis
# of divisions 1 2
# of daughter cells 4
Genetically identical?
Yes No
Chromosome #
Same as parent (2n)
Half of parent (n)
Where
Somatic cells
Sex cells
When
Throughout life
At sexual maturity
Role
Growth and repair
Sexual reproduction