I. The Cell Cycle

1. I. The Cell Cycle • There are three stages to the cell cycle: • Interphase -G1 (growth) -S (DNA Replication) -G2 (growth and addition of organelles) • Mitosis -Prophase -Metaphase -Anaphase -Telophase 3. Cytokinesis

2. I. The Cell Cycle • The Cell cycle represents the time it takes for a cell to grow, reproduce, and divide • Some cells go through the Cell Cycle much quicker than others

3. A. Interphase • Interphase is the longest part of the cell’s life • Some cells (muscle and nerve cells) remain in interphase permanenty • During interphase, the cell experiences growth, replication of DNA, and duplication of the organelles

4. B. Mitosis • Mitosis is the division of the cell’s nucleus • It occurs in four phases: • Prophase • Metaphase • Anaphase • Telophase

5. 1. Prophase • The chromatin changes into a more mature form: chromatin  chromatid  chromosomes • The nuclear membrane will disappear • The centrioles and spindle fibers will appear

6. 2. Metaphase • Chromosomes will line-up at the cell’s equator (move to the middle)

8. 3. Anaphase • The spindle fibers pull the chromosomes apart chromosomes  chromatid

9. 4. Telophase • The chromatid unwind into chromatin • The centrioles and spindle fibers disappear • The nuclear membrane reappears

10. Telophase in an animal cell:

11. C. Cytokinesis • Cytokinesis is the division of the cell membrane and cytoplasm • In plant cells, a cell plate forms in between the new cells. The cell plate eventually forms a cell wall.

12. In plant cells a cell plate forms in between the new cells and will become the cell membrane. A cell wall then forms around the cells. C. Cytokinesis

15. III. Mistakes in Mitosis • Cancer is a disease in which cells grow and divide uncontrollably, damaging parts of the body around them.

16. IV. Meiosis • Meiosis is the formation of sex cells or gametes. • Sex cells contain half the number of chromosomes that normal body cells have • normal cells in humans have 46 • sex cells in humans have 23 • When two sex cells combine they form a zygote.

17. IV. Meiosis • Meiosis is basically mitosis twice without replication after the initial mitosis. • Meiosis has two divisions: • the first division reduces the number of chromosomes (from 46 to 23) • the second division makes another copy of the cell

18. IV. Meiosis

19. A. The Results of Meiosis • In Females – one egg and three polar bodies form • In Males – four sperm cells form

20. V. Genetic Inheritance • The male sperm cell and the female egg cell join together to form a zygote • The sperm contributes 23 chromosome and the egg contributes 23 SIMILAR chromosomes • These similar chromosomes pair up and form homologous chromosomes

21. A. Karyotype • A karyotype is a picture of one’s chromosomes

22. B. Homologous Chromosomes • These chromosomes are sorted into similar pairs called homologous chromosomes • The 23rd pair tells us if it is male or female • Male XY • Female XX

23. VI. Mistakes in Meiosis • Nondisjunction is one of the most common errors that occurs in meiosis • In nondisjunction, some chromosomes fail to split apart during anaphase • This causes the resulting cells to have too many or too few chromosomes

24. VI. Mistakes in Meiosis

25. A. Trisomy 21 Trisomy 21 occurs when a person has an extra 21st chromosome. Some characteristics include slow mental development, heart problems, small head, a distinct crease in the palm of the hand

26. One day old infant