1. Meiosis – A Source of Distinction
4/10/2019
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

2. Meiosis – A Source of Distinction
4/10/2019
Meiosis – A Source of Distinction
Meiosis does two things -
1) Meiosis takes a cell with two copies of every chromosome (diploid) and makes cells with a single copy of every chromosome (haploid).
This is a good idea if you’re going to combine two cells to make a new organism. This trick is accomplished by halving chromosome number.
In meiosis, one diploid cells produces four haploid cells.
G. Podgorski, Biology 1010

3. Reduction of Chromosome Number in the First Division of Meiosis
4/10/2019
Reduction of Chromosome Number in the First Division of Meiosis
G. Podgorski, Biology 1010

4. Meiosis – A Source of Distinction
4/10/2019
Meiosis – A Source of Distinction
The second accomplishment of meiosis:
2) Meiosis scrambles the specific forms of each gene that each sex cell (egg or sperm) receives.
This makes for a lot of genetic diversity. This trick is accomplished through independent assortment and crossing-over.
Genetic diversity is important for the evolution of populations and species.
G. Podgorski, Biology 1010

5. Keys to Understanding Meiosis
4/10/2019
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

6. Meiosis
4/10/2019
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 ≈ 8,000,000.
That’s a lot of diversity by this mechanism alone.
G. Podgorski, Biology 1010

7. Another Way Meiosis Makes Lots of Different Sex Cells – Crossing-Over
4/10/2019
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

8. Meiosis
4/10/2019
Between Independent Assortment and Crossing-Over, No Two Gametes Are Identical.
G. Podgorski, Biology 1010

9. Meiosis Following a Single Chromosome Pair
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Meiosis Following a Single Chromosome Pair
Crossing over
G. Podgorski, Biology 1010

10. Meiosis
4/10/2019
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

11. Boy or Girl? The Y Chromosome “Decides”
Meiosis
4/10/2019
Boy or Girl? The Y Chromosome “Decides”
X chromosome
Y chromosome
G. Podgorski, Biology 1010

12. Boy or Girl? The Y Chromosome “Decides”
Meiosis
4/10/2019
Boy or Girl? The Y Chromosome “Decides”
G. Podgorski, Biology 1010

13. Oogenesis – A Path of Meiosis in Humans
4/10/2019
Oogenesis – A Path of Meiosis in Humans
Woman are less busy in meiosis than men – meiosis produces only a few hundred mature eggs over a lifetime.
G. Podgorski, Biology 1010

14. Spermatogenesis – Another Path of Meiosis in Humans
4/10/2019
Spermatogenesis – Another Path of Meiosis in Humans
Men are always doing meiosis, producing roughly 250,000,000 sperm per day.
G. Podgorski, Biology 1010

15. “Putting It All Together” - Fertilization
Meiosis
4/10/2019
“Putting It All Together” - Fertilization
G. Podgorski, Biology 1010

16. Meiosis
4/10/2019
What Meiosis is About
Meiosis allows the creation of unique individuals through sexual reproduction.
G. Podgorski, Biology 1010