1. Cell Division (Mitosis)
Section 10-2

2. Chromosomes
In our cells the genetic information that is carried from one generation to the next is carried by chromosomes
Chromosomes are made up of DNA
Every organism has a specific number of chromosomes
Fruit Fly =8 (4 pair)
Human = 46 (23 pair)
Carrot = 18 (9 pair)

3. Chromosomes
Chromosomes are not visible in most cells except during cell division
Before cell division, each chromosome is replicated, or copied
Because of this, at the beginning of cell division each chromosome consists of two identical sister chromatids
Each pair of chromatids are attached at an area called a centromere

4. Replicated Chromosomes
Centromere
Sister Chromatids

5. The Cell Cycle
During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells, each of which then begins the cycle again
The cell cycle consists of two distinct phases
Interphase
M (Mitotic)-phase

6. The Cell Cycle (Mitosis)

7. Interphase
Interphase is broken down into three different steps (This is not necessarily part of mitosis)
G1(Gap1)Phase
This is a period in which the cell does most of its growing
S (Synthesis)Phase
This is when the chromosomes are replicated
G2(Gap2) Phase
The organelles and other molecules required for cell division are produced

8. Cell Cycle
When the events of G2 are complete the cell is ready to enter the M (mitotic)-Phase
Mitosis can be divided into four different phases:
Depending on the type of cell:
the four phases of mitosis can last a few minutes or several days

9. 1. Prophase The longest phase of mitosis
The chromosomes become visible
Centrioles, which are two tiny structures located in the cytoplasm near the nuclear envelope, separate and move to opposite sides of the nucleus

10. Prophase The spindle fibers form
These are fanlike microtubule structure that helps to separate the chromosomes
Chromosomes become attached to the spindle fibers at the centromere of each chromatid
Nucleolus (ribosomes are made here) disappears as does the nuclear envelope

11. Prophase

12. 2. Metaphase Second phase of mitosis Lasts only a few minutes
The chromosomes line up across the center of the cell

13. Metaphase

14. 3. Anaphase Third phase of mitosis
The centromeres that join the sister chromatids separate
Allows the chromatids to separate and become individual chromosomes
These chromosomes continue to move until they have separated into two groups on opposite sides of the cell

15. Anaphase

16. 4. Telophase Fourth phase of mitosis
Everything that happened during prophase is reversed
The spindle fibers disappear
Two new nuclear membrane are formed
Chromosomes are wrapped up
Chromosomes turns back into chromatins

17. Telophase

18. Cytokinesis
At the end of mitosis, two nuclei--each with a duplicate set of chromosomes--are formed
All that remains to complete the cell cycle is cytokinesis, the division of the cytoplasm
Cytokinesis usually occurs at the same time as telophase

19. Cytokinesis Cytokinesis can take place in a number of ways
In animal cells the cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts
Each part contains its own nucleus and organelles

20. Cytokinesis in Animal Cells

21. Cytokinesis
In plants a cell plate forms midway between the divided nuclei
The cell plate gradually develops into a separating membrane
A cell wall then begins to appear in the cell plate

22. Cytokinesis in Plant Cells

23. Mitosis in Onion Root Tip