1. Unit – Cell Reproduction
Mitosis
&
The Cell Cycle
Unit – Cell Reproduction
Biology

2. How many cells do you think your body has?

3. Each of us began as a single cell,
so one important question is:
How did that single cell develop into a body with more than a trillion cells?

4. Thus, cell division is needed for growth.
The production of such a large number of body cells is accomplished by many, many repeats of a cycle of cell division in which one cell gives rise to two cells, each of which in turn gives rise to two cells, etc.
Thus, cell division is needed for growth.

5. Even in a fully grown adult, cells still undergo cell division.
Why is this useful?
Think about your skin, for example.

6. Cell Division
The two cells that come from the division of one cell are called daughter cells.
Each of the daughter cells needs to have a complete set of chromosomes.

7. What are chromosomes?
Chromosomes are
compact
spools of
DNA

8. Chromosomes Each half is called a chromatid
The chromosome (left in the picture) was isolated from a dividing cell.
Notice that the chromosome consists of two identical halves
Each half is called a chromatid

9. Chromosomes
The point where the two chromatids touch and are held together is called a centromere

10. Review chromosome structure

11. Let’s make some chromosomes
Obtain 2 white pipe cleaners and 2 of another color.
Cut white pipe cleaners into 2:
4 inch long pieces
3 inch long
2 inch long
1½ inch long

12. Let’s make some chromosomes
Pick two different colored beads. You will need 8 of each color
Put one of the colored beads on each of the white pipe cleaners and move them to the center of the pip cleaners.
Repeat by putting one of the other colored beads on each of the colored pipe cleaners

13. Each species has a certain number of chromosomes in each cell.
Chromosome Numbers
Each species has a certain number of chromosomes in each cell. 46 78 52 18

14. Sex chromosomes
Chromosomes that determine the sex of the organism
In humans, sex chromosomes are either X or Y XY XX

15. Autosomes
All the other chromosomes in an organism

16. Unsorted Human Chromosomes

17. Karyotype
Photomicrograph of the chromosomes in a dividing cell found in a human
What is the sex of the person whose chromosomes are shown here?

18. Question What percent of your genes come from your mom?
What percent of your genes come from your dad?

19. Where did my chromosomes come from?
We inherit one member of each chromosome pair from each parent. 

20. Where did my chromosomes come from?
The 46 chromosomes in our somatic cells are actually two sets of 23 chromosomes—a maternal set (from our mother) and a paternal set (from our father.)

21. Homologous chromosomes
The two copies of each chromosome
They are the same size and shape and carry genes for the same traits

22. Diploid Cells 46 Cells having two sets of chromosomes
All normal human cells are diploid cells (except reproductive cells – egg and sperm cells)
Commonly abbreviated as 2n
In humans the diploid number is 46

23. Haploid Cells
Human sperm cells and egg cells

24. Haploid Cells Contain only 1 set of chromosomes
Haploid cells have only 1 chromosome of each homologous pair and only 1 sex chromosome
Abbreviated as 1n
When a sperm (1n) and egg cell (1n) combine, the new cell will be diploid (2n)

25. A comparison
Diploid
Haploid

26. Cell Division
How do you think each daughter cell gets a complete set of chromosomes?
In each cycle of cell division, the cell first makes a copy of all of the DNA in each of the chromosomes.

27. Cell Division
After the DNA in each chromosome has been copied, the cell undergoes a type of cell division called mitosis, which carefully separates the two copies of each chromosome to opposite ends of the dividing cell, so each daughter cell ends up with a complete set of chromosomes.

28. What is the cell cycle?
The repeating set of events that make up the life of a cell
Cell division is one phase of the cell cycle

29. What is the cell cycle? Interphase G1, S, G2 phase Mitosis (M phase)
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

30. Interphase The time between cell divisions
Divided into 3 phases (G1, S, G2 phases)

31. G1 phase
Offspring cells grow to mature size

32. S phase
Cell’s DNA is copied

33. S phase
Cell’s DNA is copied

34. The time to prepare for cell division
G2 phase
The time to prepare for cell division

35. G2 phase
Centrosomes – two pairs of dark spots; it is the microtubule organizing center
Centrioles - structures in the cytoplasm from which the spindle fibers form

36. G0 phase
Cells can exit the cell cycle and enter a state called the G0 phase
Cells do not copy DNA and do not prepare for cell division

37. Division of the nucleus
Mitosis
Division of the nucleus

38. Prophase DNA tightens and coils into chromosomes
Nuclear membrane breaks down and disappears

39. Metaphase
Chromosomes line up in the center of the cell

40. Anaphase The chromatids of each chromosome separate at the centromere
chromatids move to opposite poles of cell

41. Telophase Chromosomes return to chromatin state
A nuclear membrane forms around each set of chromosomes

42. Cytokinesis The cytoplasm of the cell divides
The area of the cell membrane that pinches in and eventually separates the dividing cell into two cells is called the cleavage furrow.

43. Cytokinesis

44. Cytokinesis
Vesicles formed by the Golgi apparatus fuse at the midline of the dividing cell, forming a membrane-bound cell wall called the cell plate.

45. Plant cells in various stages of mitosis

47. Cell Cycle

48. Cancer cells

49. Cancer cells

50. Cancer cells

51. Cancer cells