1. Chapter 10 Sexual Reproduction
and Genetics
Now: Section 1: Meiosis
Later: Section 2: Mendelian Genetics
Section 3: Gene Linkage and Polyploidy

2. Meiosis Objective Questions 1. What is meiosis?
2. What is the purpose of meiosis?
3. How is meiosis different from
mitosis?

3. BIG IDEA
The purpose of meiosis is to produce 4 gametes (Sperm or Egg) containing only 1 copy of each chromosome.

4. Question 1:
What is meiosis?
Meiosis Video

5. Meiosis is one of 2 types of cell division.
What is meiosis?
Meiosis is one of 2 types of cell division.
Cell Division
Mitosis
Meiosis We
did
this
one already

6. And.. That’s The Point …
Meiosis is just another type of cell division!

7. What is the purpose of meiosis?
Question 2:
What is the purpose of meiosis?

8. What is the purpose of meiosis?
Meiosis is a process to create
4 haploid daughter cells (gametes)
each with ½ the normal number of chromosomes.
(That’s called “haploid”)

9. What is the purpose of meiosis?
Chapter 10
Sexual Reproduction and Genetics
What is the purpose of meiosis?
Let’s take a look at humans…
This is called a karyotype
Human body cells have 46 chromosomes,
23 HOMOLOGOUS pairs…

10. What is the purpose of meiosis?
Each parent contributes 23 chromosomes
23 from Dad
23 from Mom

11. What is the purpose of meiosis?
Homologous chromosomes— two paired chromosomes, one from each parent

12. “Why are gametes haploid?” you may ask.

13. Why is it important to reduce the chromosome #?
What is the purpose of meiosis?
Why is it important to reduce the chromosome #?
1st generation
2nd generation 92
3rd generation 184
4th generation

14. The point is: Meiosis is a reduction division…
Only ½ the number of chromosomes will be given to the offspring from each parent

15. Question 3:
How is Meiosis different
from Mitosis?

16. Chromosomes and Chromosome Number
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Chromosomes and Chromosome Number
Same length
Same centromere position
Carry genes that control the same inherited traits

17. How is Meiosis different from Mitosis?
Purpose is to create two identical daughter cells
Purpose is to create 4 haploid gametes
Mother cell goes through 1 cell cycle…produces 2 daughter cells…which will become 2 new mother cells.
Mother cell goes through 1 cell cycle…produces 2 daughter cells…each of which will go through another cell cycle, creating 2 gametes
Sister chromatids become visible at prophase, line up randomly at metaphase
Sister chromatids attached as TETRADS(4 chromatids together) appear at prophase, stay together at metaphase line
No genetic variation
Genetic variation

18. Haploid and Diploid Cells
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Haploid and Diploid Cells
An organism produces gametes to maintain the same number of chromosomes from generation to generation.
Human gametes contain 23 chromosomes.
A cell with n chromosomes is called a haploid cell.
A cell that contains 2n chromosomes is called a diploid cell.

19. The sexual life cycle in animals involves meiosis.
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis I
The sexual life cycle in animals involves meiosis.
Meiosis produces gametes.
When gametes
combine in fertilization, the number of
chromosomes is restored.

20. Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Stages of Meiosis I
Reduces the chromosome number by half through the separation of homologous chromosomes
Involves two consecutive cell divisions called meiosis I and meiosis II

21. Chromosomes replicate.
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis I
Interphase
Chromosomes replicate.
Chromatin condenses.
Interphase

22. Pairing of homologous chromosomes occurs.
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis I
Prophase I
Pairing of homologous chromosomes occurs.
Each chromosome consists of two chromatids.
Prophase I
The nuclear envelope breaks down.
Spindles form.

24. Crossing over produces exchange of genetic information.
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis I
Prophase I
Crossing over produces exchange of genetic information.
Crossing over—chromosomal segments are exchanged between a pair of homologous chromosomes.

25. Chromosome centromeres attach to spindle fibers.
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis I
Metaphase I
Chromosome centromeres attach to spindle fibers.
Metaphase I
Homologous chromosomes line up at the equator.

26. Homologous chromosomes separate and move
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis I
Anaphase I
Homologous chromosomes separate and move
to opposite poles of the cell.
Anaphase I

27. The spindles break down.
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis I
Telophase I
The spindles break down.
Telophase I
Chromosomes uncoil and form two nuclei.
The cell divides.

28. A second set of phases begins
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis II
Prophase II
A second set of phases begins
as the spindle apparatus forms and the
chromosomes condense.
Prophase II

29. A haploid number of chromosomes
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis II
Metaphase II
A haploid number of chromosomes
line up at the equator.
Metaphase II

30. The sister chromatids are
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis II
Anaphase II
The sister chromatids are
pulled apart at the centromere by spindle
fibers and move toward the opposite poles
of the cell.
Anaphase II

31. The chromosomes reach the poles, and
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis II
Telophase II
The chromosomes reach the poles, and
the nuclear membrane and nuclei reform.
Telophase II

32. Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis II
Cytokinesis results in four haploid cells, each with n number of chromosomes.
Cytokinesis
Visualizing Meiosis I and Meiosis II

33. The Importance of Meiosis
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
The Importance of Meiosis
Meiosis consists of two sets of divisions
Produces four haploid daughter cells that are not identical
Results in genetic variation
Mitosis and Meiosis

34. Meiosis Provides Variation
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis Provides Variation
Depending on how the chromosomes line up at the equator, four gametes with four different combinations of chromosomes can result.
Genetic variation also is produced during crossing over and during fertilization, when gametes randomly combine.

35. Sexual Reproduction v. Asexual Reproduction
Chapter 10
Sexual Reproduction and Genetics
10.1 Meiosis
Sexual Reproduction v. Asexual Reproduction
Asexual reproduction
The organism inherits all of its chromosomes from a single parent.
The new individual is genetically identical to its parent.
Sexual reproduction
Beneficial genes multiply faster over time.