1. DO NOW: Write down 2 ways something can grow.
Lesson 30
DO NOW: Write down 2 ways something can grow.
AIM: Reproduction: Sexual and Asexual Cellular level- Cell Division What is Mitosis? What is Meiosis?

2. How do cells grow? Cells can grow in two ways:
Cells can grow by increasing in size, (getting larger)
Cell can also grow by increasing their number, (dividing – Mitosis)

3. What is Mitosis?
Mitosis is a type of cellular division where a cell reproduces itself by splitting to form two new identical cells (clones).
Mitosis produces new cells from an original old one.
This is how organisms grow and replace dead or damaged cells.

4. What types of cells do mitosis?
Single cell organisms use mitosis to reproduce. Ameba, bacteria and algae.
Body cells are any cell in the body EXCEPT sperm and egg cells. Skin cells, muscle cells, nerve cells and etc.
All cells AFTER the zygote is formed.

5. The steps of Mitosis (step 1)
1) The first step in mitosis is for the cell to prepare itself to divide.
It must start doubling all its organelles. (mitochondria, ribosome, chloroplast (plants))
In the nucleus, the DNA which is spread out in long thin strings begin to condense (coil) to form chromosomes. In humans body cells there are 46 chromosomes or 23 pairs of chromosomes.
The DNA contains all the genes to make the entire organism.

6. The steps of Mitosis (step 2)
2) The chromosomes (DNA) begin to duplicate forming an “X” like shape.

7. The steps of Mitosis (step 3)
3) Now that the chromosomes are doubled, they begin to line up in the middle of the cell.

8. The steps of Mitosis (step 4)
Small fibers attached to the center of each chromosomes begin to pull the “X” shaped chromosomes apart and toward each end of the cell.

9. The steps of Mitosis (step 5)
Membranes form around the newly separated chromosomes and the cell begins to pinch at the middle.

10. The steps of Mitosis (step 6)
Finally a membrane forms at the “pinch” and two cells are formed.
The DNA unwinds itself.

12. Mitosis and Asexual Reproduction
In multicellular organisms, mitosis is a way to make more cells that the body may need. Mitosis occurs in all body cells.
In many unicellular (single cell) organisms, mitosis is the way they reproduce.
Using mitosis as a means of reproducing is a form of asexual (one parent) reproduction.
Each offspring is a clone of its parent and sibling. These cells all contain exactly the same genetic information.

13. Examples of Asexual Reproduction
Each offspring is identical to the parent

14. What is Meiosis? Meiosis is another type of cell division.
Instead of two identical cells in respect to the parent, the new cell(s) will have half the number of chromosomes.
Meiosis ONLY occurs in the sex cells (gametes) - Sperm and Egg cells.

15. Meiosis only occurs in the sex organs (testes in males, ovaries in females)
Sex cells are called Gametes

16. Why do the daughter cells have half the chromosomes?
The purpose of the sex cell in meiosis is to be able to combine with another sex cell to form a zygote with a new combination of genes.
By having only half the number of chromosomes, the union of the two sex cells will result in a zygote containing the right number of chromosomes
( ½ + ½ = whole) - one set of chromosome from the sperm (father) and one set from the egg (mother).
Human cells have 46 chromosomes or 23 pairs, therefore human gamete cell have____ non paired chromosomes.
Because 2 gametes are needed to make an offspring, this form of reproduction is called sexual reproduction. 23

17. 46 46 46 46 46 46
Meiosis Cell Division 23 23 23 23
Divides Once
Mitosis Cell Division
Divides Twice

18. Steps of Meiosis
The first part of Meiosis follows the same steps as in Mitosis, except instead of the DNA uncoiling when the cells splits, the cells split a second time.
This leaves the gamete cells without a chromosome pairs. So the number of chromosome are cut in half.

19. Fertilization: The meeting of the Gametes
When a sperm combines with an egg, fertilization occurs. Fertilization means that the chromosomes from the sperm is able to combine with the chromosomes from the egg creating the correct number of chromosome in the zygote.
This means that the zygote contain some genes from the father and some genes from the mother.
For this reason, the developing embryo will have traits (characteristics) of both the mother and the father.

20. How can I remember which cell division is which?
I use mitosis to make my own cells
My parents used Meiosis to make me.

21. VIDEO

22. Fertilization: The meeting of the Gametes (continued)
Because meiosis creates cells with only 23 non-paired chromosomes, when to gametes meet (fertilization) the new cell (zygote) will have the proper number of chromosomes (23 pair or 46 total).
As a results of the gametes combining, the offspring will have characteristics (inherit features) from both parents.

23. Fertilization: The meeting of the Gametes
In a normal human cell, the nucleus contains 23 pairs of chromosomes (a set of 23 chromosomes from the mother and a set of 23 chromosomes from the father or a total of 46 chromosomes)
Each of the 23 chromosomes are different from each other and they are labeled 1 through 23.
When the chromosomes are paired (example: mother’s chromosome 5 & father’s chromosome 5, they are said to be homologous (same))

24. Pros and Cons about Asexual and Sexual Reproduction
Produces offspring with variety; this can improve the population.
Lead to the evolution of population.
Con
Very slow because you have to find a mate.
The combination of genes can lead to individuals that have poor genes (ugly genes).
Asexual Reproduction
Pro
It is fast. Because there is no need to search for a mate, reproduction can occur quickly.
Offspring are exactly alike.
Con
No variety with in the population; everyone is the same.
If a disease kills one, that disease can possibly kill all of them.