1. Cell Reproduction Unit
Part 3:
Meiosis

2. Objectives Be able to summarize the events of meiosis I and II
Be able to compare the end products of meiosis with those of mitosis
Be able to explain crossing-over and how it contributes to the production of unique individuals
Be able to compare & contrast spermatogenesis and oogenesis

3. Meiosis
Is a process of cell division that reduces the number of chromosomes in new cells to _________
It is also the process of producing gametes
Human gametes are ________ and ________.
Each contains ______ chromosomes
half
sperm
eggs 23

4. Stages of Meiosis Two stages of meiosis: Meiosis I & Meiosis II
Prior to the first stage, cells undergo the G1, S and G2 phases of interphase
Meiosis differs from mitosis in that it happens twice and it results in 4 haploid cells

5. Mitosis Vs. Meiosis
Meiosis Video

6. Meiosis I Prophase I DNA coils into chromosomes Spindle fibers appear
The nucleolus & nuclear membrane disappear
Synapsis occurs in which:
Homologous chromosomes pair together in tetrads
The chromatids within each tetrad swap pieces in a process called crossing over
This exchange causes genetic recombination-a new mixture of genetic material

7. Crossing Over

8. Meiosis I
Metaphase I
Tetrads line up randomly in the middle of the cell
Spindle fibers attach to the ______________ of the homologous chromosomes
kinetechores

9. Meiosis I
Anaphase I
Each homologous chromosome move to opposite sides of the cell
This separation is random and is called independent assortment

10. Meiosis I Telophase I and Cytokinesis I
Chromosomes reach opposite ends of the cell
New cells produced contain a haploid number of chromosomes
2 new cells are the result

12. Meiosis II Second division stage
Occurs in each cell formed in meiosis I
This means I have 2 cells that will become 4!

13. Prophase II, Metaphase II, and Anaphase II
Spindle fibers form
Chromosomes move to the middle
Chromatids separate and move to opposite ends of the cell

14. Telophase II & Cytokinesis II
Nuclear membranes reform around the chromosomes in each of the 4 new cells
Each of 4 new cells contains half of the original cell’s number of chromosomes

16. Development of Gametes
Males
Location: _______
Gametes: _______
Process: spermatogenesis
Females
Location: _______
Gametes: _______
Process: oogenesis
Testes
Ovaries
Sperm
Eggs

17. Spermatogenesis

18. Oogenesis
Ovum

19. Gamete Formation Review
Spermatogenesis & Oogenesis