1. Cell Division

2. Chromosomes Are made of DNA
Each chromosome consists of sister chromatids attached at a centromere

3. Cell Cycle
During the cell cycle, a cell grows, prepares for division, and divides to form 2 daughter cells, each with each of which then begins the cycle again.
Interphase – time for growth and regular cell activity.
Most of a cells life is spent in Interphase.

4. Interphase

5. Mitosis The division of somatic or regular cells.
Its divided into 4 phases.
Remember Interphase is NOT part of Mitosis.

6. Introduction to Mitosis

7. Prophase First stage of Mitosis Chromatin condenses into chromosomes
Centrioles separate and a spindle fiber begins to form.
Nuclear membrane breaks down

8. Prophase

9. Metaphase Second Phase of Mitosis
Chromosomes line up in the middle of the cell.
Each chromosome is connected to a spindle fiber.

10. Metaphase

11. Anaphase Third Phase of Mitosis
The sister chromatids separate into individual chromosomes and move apart to opposite ends of the cell.

12. Anaphase

13. Telophase Fourth and Final Stage of Mitosis
Chromosomes gather at opposite ends of the cell and lose their distinct shapes
Two new nuclear membranes have formed.

14. Telophase

15. Cytokinesis The cytoplasm pinches in half.
Each daughter cell has an identical set of duplicate chromosomes

16. Regulating the Cycle
A protein call cyclin helps regulate the cell cycle in eukaryotic cells.
They respond to internal and external events. These proteins are regulators.

17. When Things Go Wrong
Cancer cells do not respond to the signals that regulate the growth of most cells.
As a result, they form masses of cells called tumors that can damage surrounding tissues.

18. Meiosis
Division of Sex Cells

19. Meiosis
A process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.
Diploid – 2 sets of chromosomes
Haploid – 1 set of chromosomes
Homologous – chromosomes that each have a corresponding chromosome from the opposite sex parent

20. Meiosis

21. Meiosis Stages Meiosis usually involves 2 distinct stages Meiosis I
Meiosis II

22. Prophase I
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
There are 4 chromosomes in a tetrad.
The pairing of homologous chromosomes is the key to understanding meiosis.
Crossing-over may occur here
Crossing-over is when chromosomes overlap and exchange portions of their chromatids.

23. Prophase I

24. Metaphase I
Spindle fibers attach to the chromosomes

25. Anaphase I
The fibers pull the homologous chromosomes toward opposite ends of the cell.

26. Telophase I & Cytokinesis
Nuclear membranes form.
The cell separates into 2 cells.

27. Prophase II Meiosis I results in two haploid (N) cells. Each cell has
half the
number of
chromosomes as the original cell.

28. Metaphase II
The chromosomes line up similar to metaphase in mitosis.

29. Anaphase II
Sister chromatids separate and move to opposite ends of the cell.

30. Telophase II
Meiosis II results in 4 haploid cells.

31. Gamete Formation In males, meiosis results in 4 sperm cells
In females, meiosis results in 1 egg cell and three polar bodies, which are not used in reproduction.

32. Mitosis vs Meiosis Mitosis Meiosis Results in 2 Diploid Cells (2N)
4 Haploid Cells (N)
Cells are
Genetically Identical
Genetically Different
Occurs in
Somatic (Body) Cells
Sex Cells