1. Mitosis VS Miosis

2. HOW MANY CHROMOSOMES ARE FOUND IN EACH HUMAN BODY CELL?
Warm-UP
HOW MANY CHROMOSOMES ARE FOUND IN EACH HUMAN BODY CELL?

3. Section 10.2 Summary – pages 263-273
In the body cells of animals and most plants, chromosomes occur in pairs.
In each pair, you inherited one from your mom, the other from your dad.
From Mom
From Dad
Section 10.2 Summary – pages

4. Section 10.2 Summary – pages 263-273
Homologous Chromosomes
The two chromosomes of a pair are called homologous chromosomes.
Each pair of homologous chromosomes has genes for the same traits.
Section 10.2 Summary – pages

5. Section 10.2 Summary – pages 263-273
Diploid Cells
A cell with two of each kind of chromosome is called a diploid cell or somatic (body) cells.
All of your body cells are diploid (2n).
Section 10.2 Summary – pages

6. Section 10.2 Summary – pages 263-273
Each person can only pass on ONE of their homologous chromosomes to their young.
HUMANS = 46 CHROMOSOMES
IN THEIR BODY CELLS
Each parent passes 23 to their young.
Sperm(23)+Egg(23)=46 chromosomes
Section 10.2 Summary – pages

7. Section 10.2 Summary – pages 263-273
Haploid Cells
A cell containing only one of each kind of chromosome is called a haploid cell (n).
Sex cells (gametes) are haploid cells.
Section 10.2 Summary – pages

8. Section 10.2 Summary – pages 263-273
Sexual Reproduction
Zygote
Section 10.2 Summary – pages

9. ● Body cells are made by the division process MITOSIS.
Since they have different amounts of chromosomes, they are made in different ways
● Body cells are made by the division process MITOSIS.
● Sex cells are made by the division process MEIOSIS.

10. The cell cycle (or entire life cycle of the cell) consists of:
Before a cell can divide by either method, it must first prepare for cell division.
The cell cycle (or entire life cycle of the cell) consists of:
INTERPHASE: The longest/busiest stage in a cell’s life
1. Chromosomes (DNA) replicates
2. Cell grows bigger
NUCLEAR DIVISION: Mitosis or Meiosis
CYTOKINESIS: When the cytoplasm divides and the cell completely separates.

11. Mitosis: cell division that makes BODY CELLS.46
It starts with a DIPLOID cell
Chromosomes Replicate 92 46 46
It ends with TWO IDENTICAL DIPLOID cells

12. The cell division process that occurs in haploid cells is called meiosis.
Meiosis I
Meiosis II

14. Meiosis: cell division that makes SEX CELLS.46
It starts with a DIPLOID cell
Chromosomes Replicate 92 46 46 23 23 23 23
It ends with FOUR HAPLOID cells (NOT identical)

15. Takes place during Prophase I
Crossing-Over
During Meiosis:
Homologous chromosomes actually break and exchange traits- in a process known as crossing over.
Takes place during Prophase I

16. Crossing over can occur at any location on a chromosome, and it can occur at several locations at the same time.
This causes the traits found in each gamete varied. This is why siblings of the same parents can look so different from each other.

17. Section 10.2 Summary – pages 263-273
Nondisjunction
The failure of homologous chromosomes to separate properly during meiosis is called nondisjunction.
This would occur when homologous chromosomes are suppose to separate from each other.
Section 10.2 Summary – pages

18. Section 10.2 Summary – pages 263-273
Meiosis
When a sperm fertilizes an egg, the resulting zygote once again has the diploid number of chromosomes.
VIDEO
Zygote = a fertilized egg
Section 10.2 Summary – pages

19. Get your comp book 1. Put in your Meiosis Notes 2
Get your comp book 1. Put in your Meiosis Notes Prepare a page for “Crossing Over/ Genetic Variation”
In this activity, you will model Crossing over that occurs during Prophase I of Meiosis and discover how this small event causes genetic variation in siblings.

20. Take your strip of paper
This will end up being one homologous pair of chromosomes.
The six bands will represent different genes
What are genes?

21. # The bands 1-6 starting at the top
Write the # of the band on both sides

22. Color the bands as follows:
1. Blue
2. Red
3. Purple
4. Green
5. Brown
6. Yellow
Label the Type of Gene at
the bottom of each band…
1. Dimples
2. Hair Texture
3. Tongue Curl
4. Hitch Hiker Thumb
5. Cleft Chin
6. Anxiety

23. Cut your strip in half long-ways
These two strips represent Homologous chromosome pair #1

24. For example: In the “Hair Texture” band you could write
6. For each chromosome, assign a characteristic that was passed down for each gene.
For example: In the “Hair Texture” band you could write
Straight, Curly, or Wavy
Give only 1 characteristic per gene

25. Homologous Chromosome Pair #1
Pretend this homologous pair is in either a Spermatocyte or Oocyte…
and it is time for Meiosis

26. Homologous Chromosomes break and exchange genes (Crossing Over)
During Meiosis
Prophase I
Homologous Chromosomes break and exchange genes (Crossing Over)
7. Cut away two genes on both chromosomes and exchange them

27. Tape up your newly crossed-over chromosomes.
This ‘mixes it up’
So your chromosomes should still have the same genes in the same order 1-6, BUT have a different mix of characteristics than before.

28. 9. Find someone in class and trade ONE of your homologous chromosomes.
During Anaphase your chromosomes are parted from each other and are put in different sex cells.
When one of these sex cells unites with another then the new baby will have a complete set of homologous chromosomes.
9. Find someone in class and trade ONE of your homologous chromosomes.

29. Pretend you and your classmate have created siblings (two children from the same parents)
Tape/glue your sibling’s homologous pair #1 in your comp book.
-One chromosome should be yours
-The other chromosome should be from the other parent.
Answer the questions on the next slide about crossing over and genetic variation.

30. Answer these questions in your comp. book:
How does Crossing Over create genetic variation?
Specifically how were the genes/characteristics different in the siblings even though they came from the same parents?
Why is Crossing over important in Meiosis?
Are there any traits that your sibling could possibly pass down to the next generation that the other sibling could not? EXPLAIN.