1. Set up Cornell Notes on pg. 77 Topic: 6.2 Process of Meiosis
Essential Questions:
On Pg. 66 please make a detailed flow map of the phases of meiosis I and II
Must have color
Picture
Description (in your own words)
6.2 Process of Meiosis
2.1 Atoms, Ions, and Molecules
On Pg. 66 please make a detailed flow map of the phases of meiosis
Must have color
Picture
Description (in your own words)

2. KEY CONCEPT During meiosis, diploid cells undergo two cell divisions that result in haploid cells.

3. Germ cells (46) develop into gametes through meiosis
Meiosis reduces chromosome number (46 to 23) and creates genetic diversity.
All organisms that reproduce sexually must undergo meiosis

4. Homologous Chromosomes
Homologous chromosomes are very similar to one another
Carry the same genes
One from Mom
One from Dad

5. Crossing over during meiosis increases genetic diversity.
Crossing over is the exchange of chromosome segments between homologous chromosomes.
occurs during prophase I of meiosis I
results in new combinations of genes

6. Chromosomes contain many genes.
The farther apart two genes are located on a chromosome, the more likely they are to be separated by crossing over.

7. Genes located close together on a chromosome tend to be inherited together, which is called genetic linkage.

8. Meiosis has 2 cell divisions
Results in 4 unique haploid cells 1 2

9. Meiosis I
occurs after DNA has been replicated in the S stage
Meiosis I divides homologous chromosomes in four phases.

10. Dad
Prophase I:
The nuclear membrane breaks down
duplicated chromosomes condense
homologous chromosomes pair up
Appear to pair up precisely, gene for gene
Mom
Dad
Mom

11. Dad
Mom
Metaphase I:
Homologous chromosomes randomly align along the cell equator (middle)
Which creates genetic diversity
Each side of equator has chromosomes from both parents
Dad
Mom

12. If, during metaphase I, all 23 maternal chromosomes lined up on the same side of the cell, would genetic diversity increase?

13. 1. Genetic diversity would not increase because the maternal and paternal chromosomes would not become arranged in new combinations.

14. Anaphase I:
The homologous pairs separate from each other and move to opposite sides of the cell
Sister chromatids remain attached

15. Telophase I:
Nuclear membrane forms
The cell undergoes cytokinesis
Each cell has a unique combination of 23 duplicated chromosomes from both parents

17. Meiosis II
divides sister chromatids in four phases
DNA is not replicated between meiosis I and meiosis II

18. Prophase II:
The nuclear membrane breaks down
The centrosomes move to opposite sides of the cell and spindle fibers form

19. Metaphase II:
Spindle fibers align the chromosomes along the cell equator

20. Anaphase II:
The sister chromatids are pulled apart from each other and move to opposite sides of the cell.

21. Telophase II:
The nuclear membranes form again around the chromosomes
spindle fibers break
cell undergoes cytokinesis
RESULT: 4 unique haploid cells, with a combination of chromosomes from both the mother and father

23. Meiosis I
Meiosis II

24. Meiosis differs from mitosis in significant ways.
Meiosis has two cell divisions while mitosis has one.
In mitosis, homologous chromosomes never pair up.
Meiosis results in haploid cells; mitosis results in diploid cells.

25. Haploid cells develop into mature gametes.
Gametogenesis (gamet-o-genesis) is the production of gametes from haploid cells.
Includes both meiosis and other changes that produce a mature cell
differs between females and males.

26. Sperm:
Much smaller than the egg
Main contribution to embryo is DNA
Must be able to move- has a tail that allows it to swim to egg
During gametogenesis:
DNA tightly packed
Much cytoplasm is lost, forming a head
Forms a flagellum
Forms neck region- packed with mitochondria that drives cell
Addition of new proteins

27. Eggs:
Eggs contribute DNA, cytoplasm, and organelles to an embryo.
During meiosis, the egg gets most of the contents; the other cells form polar bodies.
Begins before birth
Not finished until egg is fertilized
Only one of the 4 haploid cells actually becomes an egg
The other 3 become polar bodies- only DNA inside

28. Sexual reproduction creates unique combination of genes.
random fertilization of gametes
Unique phenotypes may give a reproductive advantage to some organisms.
Sperm= 8 million different combinations
Egg= 8 million different combinations
Any sperm can fertilize any egg= 64 TRILLION possible combinations

29. Meiosis #: Name of Phase
Meiosis I
Prophase I
Metaphase I
Anaphase I
Telophase I
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis #: Name of Phase
PICTURE
Short description of what is happening in this phase