1. Meiosis
Formation of Sex Cells to Transfer Genetic Information to the Next Generation

2. Mitosis and Meiosis in the Human Life Cycle
Diploid number of chromosomes, two full sets
Mitosis and Meiosis in the Human Life Cycle
Nuclear division retaining the original chromosome number
Nuclear division reducing the chromosome number, leading to sperm or eggs
Haploid number of chromosomes, one full set

3. Mitosis and Meiosis Human Cell with 46 chromosomes (DIPLOID)
Interphase Mitosis Cytokinesis
Interphase Meiosis Cytokinesis
2 Genetically-Identical
Human Cells each with
46 chromosomes
(DIPLOID)
4 Genetically-Different Human Cells each with
23 chromosomes
(HAPLOID)

4. Homologous Chromosome Pairs
Diploid cells have pairs of chromosomes
Each homologous chromosome pair is genetically matched so that the genes are arranged in the same order
Meiosis distributes members of each pair to separate nuclei
Figure: 11.UN06b
Title:
Formation of daughter chromosomes
Caption:
Humans have 1 pair of sex chromosomes and 22 pairs of autosomes

5. Cell Cycle With Meiosis
Interphase includes
G1 = growth phase 1
S = synthesis phase
G2 = growth phase 2
Meiosis
cytokinesis G2
synthesis of proteins and assembly of
components
for division
Meiosis I
Meiosis II
cytokinesis
Meiosis includes two chromosomal divisions Meiosis I Meiosis II
Cytokinesis = division of cytoplasmic contents S
chromosomes
duplicate G1
cytoplasm
doubles,
including organelles
Interphase

6. Applying Your Knowledge
G1 phase
S phase
G2 phase
Meiosis I and II
When does chromosomal division occur?
When do the cytoplasmic contents double?
When does chromosome duplication occur?

7. Meiosis Involves Two Chromosomal Divisions
Equational Division: Separation of sister chromatids, no change in chromosome number
Reduction Division: Separation of homologous chromosomes, reducing the chromosome number to haploid
Meiosis Involves Two Chromosomal Divisions

8. Duplicated Chromosomes in Early Meiosis
Homologous Chromosome Pair
Duplicated chromosomes joined at their centromeres
Nonsister Chromatids are joined to different centromeres
Centromere = constricted region
Duplicated Chromosomes in Early Meiosis

9. Prophase I of Meiosis I Chromosomes thicken
Genetic exchange occurs between nonsister chromatids through crossing-over

10. Metaphase I of Meiosis I
Spindle fiber
Homologous pairs line up at the cell equator
Spindle fibers attached to centromeres cause chromosomal movement

11. Anaphase I and Telophase I of Meiosis I
Members of homologous pair separate and are pulled to opposite poles of the cell
Telophase I
Chromosomes reach opposite poles
+ cytokinesis
Cytokinesis
Cytoplasm divides into two separate cells
Daughter cells are haploid with duplicated chromosomes

12. Prophase II and Metaphase II of Meiosis II
Chromosomes thicken
Metaphase II
Chromosomes line up at cell equator

13. Anaphase II and Telophase II of Meiosis II
Sister Chromatids separate and move to opposite poles
Telophase II
Chromosomes have reached opposite poles
+ cytokinesis
Cytokinesis
Cytoplasm divides into separate cells
Daughter cells are haploid and have genetic differences

14. Applying Your Knowledge
Prophase I
Metaphase I
Anaphase I
Metaphase II
Anaphase II
When do sister chromatids separate?
When does crossing-over occur?
When do homologous pairs line up at the cell equator?

15. Equal divisions of cytoplasm Four functional products per meiosis
Sperm formation
Equal divisions of cytoplasm
Four functional products per meiosis
Fertilization occurs after Meiosis I and stimulates Meiosis II
Egg formation
Unequal divisions of cytoplasm
Small polar bodies formed
One functional product per meiosis

16. Comparing Mitosis and Meiosis
Cell type at start
Cell type at end
Are products identical? (Y/N)
Number of cells produced
Number of chromosome duplications
Pairing of homologues (Y/N)
Crossing-over (Y/N)
Number of chromosome divisions

17. Comparing Mitosis and Meiosis
Cell type at start
Cell type at end
Are products identical? (Y/N)
Number of cells produced
Number of chromosome duplications
Pairing of homologues (Y/N)
Crossing-over (Y/N)
Number of chromosome divisions
Diploid
Diploid
Diploid
Haploid
Yes No 2 4 1 1 No
Yes No
Yes 1 2