1. Today’s Date Here
6.) Meiosis – process of reduction division in which the number of chromosomes is cut in half.
Goes from diploid(2N) to 4 genetically different haploid(N) gametes

2. What needs an answer, but doesn't ask a question?
Brainteaser
What needs an answer, but doesn't ask a question?

3. Which of the following is a true statement about asexual reproduction?
Only one organism is needed.
A mutation needs to occur.
Meiosis is necessary.
DNA is not required.

4. Lets Review!
Cell Cycle
Mitosis
Types of Asexual Reproduction

5. Cell cycle consists of 2 major phases
Interphase, where chromosomes duplicate and cell parts are made
The mitotic phase, when nuclear division occurs
Figure 8.5

6. Prophase? Metaphase? Anaphase? Telophase?

7. Today you will learn What is meiosis? What is the purpose of meiosis?
Where does crossing over and independent assortment occur?
How many daughter cells are produced?

8. Meiosis – A Source of Distinction
11/6/2018
Meiosis – A Source of Distinction
Why do you share some but not all characters of each parent?
What are the rules of this sharing game?
At one level, the answers lie in meiosis.
G. Podgorski, Biology 1010

9. Why do we need meiosis?
Meiosis is necessary to halve the number of chromosomes going into the sex cells
Why halve the chromosomes in gametes?
At fertilisation the male and female sex cells will provide ½ of the chromosomes each – so the offspring has genes from both parents

10. Keys to Understanding Meiosis
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Keys to Understanding Meiosis
Chromosomes are paired.
Chromosomes carry genes.
The gene forms on a pair of chromosomes may be identical ..
Brown eyes
Tall
Brown eyes
Blue eyes
Tall
Short
or different.
G. Podgorski, Biology 1010

11. Meiosis – A Source of Distinction
11/6/2018
Meiosis – A Source of Distinction
Meiosis does two things :
Meiosis takes a cell with two copies of every chromosome (diploid) and makes cells with a single copy of every chromosome (haploid).
Meiosis scrambles the specific forms of each gene that each sex cell (egg or sperm) receives through crossing over and independent assortment.
G. Podgorski, Biology 1010

12. MEIOSIS
The process by which one diploid cell creates four haploid cells
Diploid Cell (2n) – a cell that contains both sets of homologous chromosomes
Haploid Cell (n) – a cell that contains one set of homologous chromosomes
Homologous Chromosome – corresponding (matching) chromosomes from a female and male parent.
ilt=MM Imfm Itorrol.g.si elo2oloyoS

13. Structure of Chromosomes
Homologous chromosomes are identical pairs of chromosomes.
One inherited from mother and one from father
made up of sister chromatids joined at the centromere.
Copyright © McGraw-Hill Companies Permission required for reproduction or display

14. HOMOLOGOUS CHROMOSOMES

15. MEIOSIS Meiosis has 2 parts and phases similar to Meiosis
Meiosis I – PMAT
Meiosis II - PMAT

16. MEIOSIS INTERPHASE – cells undergo DNA replication forming MEIOSIS I
Prophase I – sister chromatids pair up forming a homologous chromosome

17. Meiosis
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One Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment
Independent assortment produces 2n distinct gametes, where n = the number of unique chromosomes.
In humans, n = 23 and 223 ≈ 8,000,0000.
That’s a lot of diversity by this mechanism alone.
G. Podgorski, Biology 1010

18. Another Way Meiosis Makes Lots of Different Sex Cells – Crossing-Over
11/6/2018
Another Way Meiosis Makes Lots of Different Sex Cells – Crossing-Over
Crossing-over multiplies the already huge number of different gamete types produced by independent assortment.
G. Podgorski, Biology 1010

19. MEIOSIS
CROSSING OVER
When two chromosomes exchange portions of their chromatids
Occurs during Prophase I

20. MEIOSIS
MEIOSIS I
Metaphase I – Spindle fibers attach to the chromosome.

21. Meiosis
11/6/2018
The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis
Mitosis
The first (and distinguishing) division of meiosis
G. Podgorski, Biology 1010

22. MEIOSIS
MEIOSIS I
Anaphase I – Spindle fibers pull the homologous chromosomes toward opposite ends of the cell.

23. MEIOSIS
MEIOSIS I
Telophase I - Meiosis I results in 2 haploid (n) daughter cells. Each with half the number of chromosomes as the original cell

24. MEIOSIS II
MEIOSIS II
Prophase II – 2 haploid (n) daughter cells. Each with half the number of chromosomes as the original cell.

25. MEIOSIS II
MEIOSIS II
Metaphase II – The chromosomes line up in a similar way to the metaphase stage of mitosis

26. MEIOSIS II
MEIOSIS II
Anaphase II – The sister chromatids separate and move toward opposite ends of the cell

27. MEIOSIS II
MEIOSIS II
Telophase II – Meiosis II results in four haploid (n) daughter cells.

28. Meiosis Parent cell – chromosome pair Chromosomes copied
1st division - pairs split
2nd division – produces 4 gamete cells with ½ the original no. of chromosomes

29. Boy or Girl? The Y Chromosome “Decides”
Meiosis
11/6/2018
Boy or Girl? The Y Chromosome “Decides”
G. Podgorski, Biology 1010

30. Meiosis – mouse testes
Parent cell
1st division
2nd division
4 gametes

31. Oogenesis – A Path of Meiosis in Females
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Oogenesis – A Path of Meiosis in Females
Woman are less busy in meiosis than men – meiosis produces only a few hundred mature eggs over a lifetime.
G. Podgorski, Biology 1010

32. Spermatogenesis – Another Path of Meiosis in Males
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Spermatogenesis – Another Path of Meiosis in Males
Men are busy – meiosis produces roughly 250,000,000 sperm per day.
G. Podgorski, Biology 1010

33. “Putting It All Together” - Fertilization
Meiosis
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“Putting It All Together” - Fertilization
G. Podgorski, Biology 1010

34. Boy or Girl? The Y Chromosome “Decides”
Meiosis
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Boy or Girl? The Y Chromosome “Decides”
X chromosome
Y chromosome
G. Podgorski, Biology 1010

35. Meiosis
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What Meiosis is About
Meiosis allows the creation of unique individuals through sexual reproduction.
G. Podgorski, Biology 1010

36. Which process requires meiosis?
egg production
bacterial fission
flatworm regeneration
vegetative propagation