1. The cell division of love (and diversity) <3
Meiosis
The cell division of love (and diversity) <3
EQ: How does the sorting and recombination of genes in meiosis result in a greater genetic variation?

2. Meiosis Chromosomes
Duplicated Homologous chromosome made of 2 sister chromatids held together at centromere
Each chromatid contain identical copies of DNA
Each Chromosome may contain different variations
Homologous duplicated
chromosomes
homologous
chromosomes
Homo = same
THIS IS MEIOSIS
Logos = word or plan
single-stranded
sister chromatids
double-stranded

3. Homologous Chromosomes vs. Sister Chromatids
Homologous Chromosomes: two duplicated chromosomes containing the same genes (eye color/hair color)
Could contain different variations of the same genes.
Divided during meiosis I
Sister Chromatids: one half of the duplicated chromosome
Sister chromstids contain the exact same copy of genes
The duplicated sides of the chromosome that remain attached at the centromere
Divided during meiosis II
sister
chromatids
sister
chromatids

4. Chromosomes
Autosomes: chromosomes that contain genes for characteristics NOT related to the sex of an organism
Chromosome pairs 1-22 in humans
Sex Chromosomes: directly control the development of sexual characteristics
Pair 23 – in mammals, the X and Y chromosomes determine gender
Female = X X
Male = X Y

5. Sex Chromosomes The X chromosome The Y chromosome
larger sex chromosome
contains genes that have nothing to do with sexual characteristics
The Y chromosome
the smallest chromosome
The genes on this chromosome direct the development of testes and other male traits

6. Types of Cells Somatic Cells: Gametes: body cells
Diploid – Contains two copies of chromosomes (46)
Produced by Mitosis
Ex. skin cells, liver cells
Gametes:
sex cells
Haploid- Contain half the number of chromosomes (23)
Produced by Meiosis
Ex. eggs (female) and sperm (male)

7. Gametes
(Sex Cells) - 23
Somatic Cells
(Body Cells)- 46

8. Sexual Reproduction:
Sexual reproduction- process by which two gametes fuse during fertilization and the offspring are a genetic mixture of both parents
Benefits:
Allows genetic variation in offspring- differences in appearances that offspring show from their parents.
Allows for the ability to adapt to
environmental changes

9. What must happen before a cell can divide?
INTERPHASE!!!!
DNA must Duplicate!

10. Gametes are haploids, Which means?
Sex cells have half the chromosomes as somatic cells.
Think/Pair/Share
How do you think they get to have half the number of chromosomes?

11. Steps of Meiosis Interphase I Meiosis I Prophase I : Crossing Over
G1, S, G2 (Cell growth and DNA rep)
Meiosis I
Prophase I : Crossing Over
Metaphase I: Independent assortment
Anaphase I
Telophase I
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
Students are not writing this page down.

12. Meiosis 1 Main points: Interphase occurs = DNA replication
Crossing over occurs = exchange of genetic material
Homologous chromosomes separate
Results in 2 diploid daughter cells

13. Prophase I Homologous chromosomes pair up nuclear membrane breaks down
Centrioles move apart
crossing over can occur

14. Crossing Over exchange of chromosomes segments during prophase I
Create new combinations
during prophase I
sister chromatids intertwine and swap pieces of chromosome
Skip to bottom on notes

15. Metaphase I homologous chromosomes align along the middle of the cell
each side has a chromosome from each parent
Independent assortment occurs
Random alignment of homologous chromosomes (genetic variation)

16. Anaphase I
the paired homologous chromosomes split and move towards centrioles at opposite poles
sister chromatids are still attached

17. Telophase I spindle fibers fall apart
nuclear membrane reforms around chromosomes
2 nuclei

18. Cytokinesis Cytoplasm divides two diploid cells are produced
How many chromosomes are in a diploid cell? 46

19. The value of meiosis 1 Consistency over time
keeps chromosome number same from generation to generation
Mom
from Mom
Consider the greater variation with 23 pairs of chromosomes = mixing and matching
Dad
offspring
from Dad

20. Meiosis II Main Points: No interphase = no DNA replication
Sister chromatids separate
Results in 4 genetically different, haploid gametes (n)

21. Prophase II centrioles move to opposites sides
nuclear envelope breaks down

22. Metaphase II
spindle fibers align sister chromotids along the metaphase plate (middle)

23. Anaphase II
sister chromatids are pulled apart towards opposite sides of the cell by centrioles

24. Telophase II
spindle fibers fall apart
nuclear membrane forms

25. Cytokinesis Cytoplasm divides Produces 4 haploid gametes
Each gamete is genetically unique

26. new gametes made by offspring
The value of Meiosis II
Change over time
introduces genetic variation
No two gametes are the same
new gametes made by offspring
Consider the greater variation with 23 pairs of chromosomes = mixing and matching
from Dad
variation
from Mom
offspring

28. Results – reduction division
1 diploid divides into FOUR HAPLOID DAUGHTER (gametes)
Reduces the number of chromosomes to 23
Each gamete is unique from one another (and parent)
Female gametes are eggs and male gametes are sperm

29. Stop and think
How does the process if meiosis produce haploid cells instead of diploid?
There is only one round in interphase and two rounds of division
Why is it important that the gametes produced in meiosis are haploid and not diploid?
During fertilization the zygote has the correct number of chromosomes
Why is meiosis called reduction division?

30. Putting it all together…
meiosis  fertilization  mitosis + development
gametes 46 23 46 23 46 46 46 46 46 23
meiosis 46 46
egg 46 46 23
zygote
fertilization
mitosis & development
mitosis
sperm

31. The whole Process

32. LAB REVIEW What is a centriole? What is a centromere?
Where are they located?
What is a centromere?
What is divided in Meiosis 1?
What is divided in Meiosis 2?
What materials represent:
Chromosomes
Centrioles
Centromeres
Nucleus
Cell
Spindle fibers

33. Meiosis Gummy Worm Lab C: Level 2 voice
H: Work with table group (Raise hand for help)
A: Meiosis lab and answer the analysis questions
M: Remain seated at assigned table
P: complete own sheet and paste into your notebook
Success!

34. Exit ticket
Clear desk of everything except DO NOW and something to write with