1. Meiosis Why do you share some but not all characters of each parent?
2/21/2019
Meiosis
Why do you share some but not all characters of each parent?
What are the rules of this sharing game?
G. Podgorski, Biology 1010

2. Asexual reproduction is reproduction
that requires only one parent.
• Most single-celled organisms, like bacteria
and protozoans, reproduce this way.

3. Cell division is a type of asexual
reproduction.
• Your body cells reproduce this way.
• In asexual reproduction, the DNA and internal structures are copied.
• Then the parent cell divides, forming two cells that are exact
copies of the original.

4. Meiosis
2/21/2019
What Meiosis is About
Meiosis allows the creation of unique individuals through sexual reproduction.
G. Podgorski, Biology 1010

5. Keys to Understanding Meiosis
2/21/2019
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: A type of cell division that results in daughter cells with half as many chromosomes as the parent cells

7. • Meiosis is the process of cell division in which gametes -sex cells (eggs and sperm) are formed

8. n = number of chromosomes from each parent
Meiosis
2/21/2019
n = number of chromosomes from each parent
Gametes are haploid diploid(n)
Body cells are diploid 2(n) – cells with two of each kind of chromosome
G. Podgorski, Biology 1010

9. Chromosomes
Humans: 46 (23 pairs)
Mosquito: 6 (3 pairs)
Toad: 22 (11 pairs)
Potato: 48 (24 pairs)
Dog: 78 (39 pairs)

10. Homologous chromosomes are paired chromosomes with genes for the same traits arranged in the same order

11. Bellringer Thu, 12/04 What are gametes? What is a gene?
Name the 2 processes that meiosis does to
scramble genes and create variety in the gametes.
USE YOUR NOTES FROM YESTERDAY!!!
REMINDERS: HW #14 due Fri, Progress Reports,
LAB FEE anytime, Notebook check tomorrow!!!

12. Stages of Meiosis: Meiosis I
Stages of Meiosis: PMAT I and II
Meiosis I: reduces chromosome number

13. Stages of Meiosis: Meiosis II
2/21/2019
Meiosis II: separates chromatids
G. Podgorski, Biology 1010

14. Prophase I: homologous pairs (and copies) synapse or pair up
Prophase I: chromatin condenses, homologous pairs (with copies) align Metaphase I: homologous pairs (and copies) align at metaphase plate
Meiosis
2/21/2019
Meiosis I
Prophase I: homologous pairs (and copies) synapse or pair up
Metaphase I: chromosomes align at the middle at the equator of the cell
G. Podgorski, Biology 1010

15. Meiosis I continued
Anaphase I: homologous chromosomes (each with two chromatids) move to opposite ends Telophase I:two nuclei form, original cell divides

16. Meiosis II: PMAT part II
No INTERPHASE or DNA copied between I and II
Prophase II: chromosomes condense again and start to move toward the equator
Metaphase II chromosomes line up in the middle

17. Meiosis II continued
Anaphase II: chromatids separate to opposite poles Telophase II: two nuclei form - and cells divide
Cytokinesis as in mitosis!

18. Results after meiosis…
In males -Four sperm cells are formed
All sex cells are haploid (n) - half as many chromosomes as parent cell (2n)

19. In females meiosis results in one large egg cell and 3 polar bodies
2/21/2019
In females meiosis results in one large egg cell and 3 polar bodies
Women are less busy in meiosis than men – meiosis produces only a few hundred mature eggs over a lifetime.
G. Podgorski, Biology 1010

20. In males meiosis results in 4 sex cells
2/21/2019
In males meiosis results in 4 sex cells
Men are busy – meiosis produces roughly 250,000,000 sperm per day.
G. Podgorski, Biology 1010

21. Meiosis
2/21/2019
The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis
The first (and distinguishing) division of meiosis
Mitosis
G. Podgorski, Biology 1010

22. Crossing-over -exchange of genetic material between homologous pairs
Meiosis
2/21/2019
Crossing-Over
Crossing-over -exchange of genetic material between homologous pairs
G. Podgorski, Biology 1010

23. Chromosomes 1 to 22 are autosomes Chromosome #23 sex chromosome
Meiosis
Chromosomes 1 to 22 are autosomes
Chromosome #23 sex chromosome
2/21/2019
G. Podgorski, Biology 1010

24. Boy or Girl? The Y Chromosome “Decides”
Meiosis
2/21/2019
Boy or Girl? The Y Chromosome “Decides”
X chromosome
Y chromosome
G. Podgorski, Biology 1010

25. Meiosis
2/21/2019
G. Podgorski, Biology 1010

26. Boy or Girl? The Y Chromosome “Decides”
Meiosis
2/21/2019
Boy or Girl? The Y Chromosome “Decides”
G. Podgorski, Biology 1010

27. “Putting It All Together” - Fertilization
Meiosis
2/21/2019
“Putting It All Together” - Fertilization
G. Podgorski, Biology 1010

28. Meiosis
2/21/2019
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 ≈ 8,000,0000.
That’s a lot of diversity by this mechanism alone.
G. Podgorski, Biology 1010

29. A fertilized egg, called a zygote, has a
diploid set of chromosomes.
• For each homologous pair,
one chromosome comes
from the mother, and one
from the father.
• After fertilization, the
zygote rapidly divides by
mitosis and becomes an
embryo.