1. Meiosis
Sexual Reproduction

2. Where do you come from?

3. Sex: Woman, XX Man, XY Gender: Female Male Egg, Ovum Sperm

4. Fertilization – union of sperm an egg to produce zygote

5. Sperm and egg cells – gametes
Fertilization
Sperm and egg cells – gametes

6. Fetus Development
Fertilization Mitosis to Create More Cells Fetus

7. 23 pairs of chromosomes
1 from mom,1 from dad
46 individual chromosomes
Body cells have all these chromosomes – diploid (2n)
Gametes have ½ the amount because they will combine to eventually form body cells– haploid (n)
(hap  half)

8. Homo sapiens – 46 chromosomes, 23 pairs

9. Diploid and Haploid Practice

10. Got it? Questions
In humans, the cardiac muscle cells, skin cells, and neurons, of humans all have ____________ chromosomes
The sperm and egg cells are called ______________
In humans an ovum (egg cell) would have _____ chromosomes
When a cell like a gamete has ½ the amount of chromosomes it is called ___________and symbolized as n
When a body cell like a skin cell has the full amount of chromosomes it is called __________, and symbolized as 2n
If a sperm cell has 8 chromosomes it came from a male with _____ chromosomes. 46
gametes 23
haploid
diploid 16

12. Meiosis (My-oh-sis)
Definition: Process by which 1 diploid eukaryotic cell divides twice to generate 4 haploid gametes
Gametes – sperm or cells
Produces 4 cells each with 1 copy of each chromosome
Purpose:
When the egg is fertilized by a sperm the new zygote has the same number of chromosomes as the parents
Zygote has 2 of each chromosomes (1 from mom, 1 from dad)
Allows multicellular organisms to reproduce sexually
Animation:

13. Special cells that divide in meiosis to become sperm and egg
Start off diploid (2n)

15. Meiosis Phases – watch the chromosomes move
Centromeres divide the chromosome short arm and long arm.
Chromatids or sister chromatids (two identical copies of DNA) are connected by the centromere
Telomeres protect DNA, during DNA replication.

17. Purpose Continued Provides great genetic diversity
Offspring have the same # of chromosomes as parents
Some of those chromosomes came from each parent
Offspring typically have characteristics from both parents

18. Prophase I Nuclear envelope breaks down DNA condenses into chromosomes
Each chromosome has 2 sister chromatids
Homologous Chromosomes Pair
Different from Mitosis
Crossing over occurs, which creates
Genetic diversity!!!

19. Crossing Over
Sections of DNA from the chromosome of one parent are switched with the same section from the other parents DNA
Allows one chromosome to contain alleles from both parents
Occurs homologous chromosomes line up at equator
Increases genetic diversity

20. Metaphase I Homologous Chromosomes line up along equator of the cell
2 Homologous Chromosomes = 4 Sister Chromatids
Which side each homolog lines up on is random
50-50 chance a daughter cell will get a chromosome from mother or father

21. Anaphase I Homologous Chromosomes are separated
Each with 2 Sister Chromatids
1 of each homologous chromosome moves to opposite ends of the cell
Results in 1 of each chromosome (2 sister chromatids) at each end

22. Telophase I (Final Phase)
Nuclear envelope may reform
2 haploid nuclei are produced
Each has 1 of each chromosome

23. Cytokinesis Not part of Meiosis I Occurs as Meiosis I is ending
Cell divides

25. Result of Meiosis I and Cytokinesis
2 genetically different cells (Remember Crossing Over)
Each cell contains 1 copy of each chromosomes
2 Sister Chromatids each

26. Prophase II Nuclear envelope breaks down
DNA condenses into chromosomes
Each chromosome has 2 sister chromatids

27. Metaphase II Sister Chromatids line up along equator of the cell
1 of each Chromosome
2 Sister Chromatids
Different than Mitosis and Meiosis I

28. Anaphase II Sister Chromatids are separated
1 of each chromosome moves to opposite ends of the cell
Results in 1 of each chromosome (no sister chromatids) at each end

29. Telophase II (Final Phase)
Chromosomes unwind
Nuclear envelope reforms in each new cell
4 haploid nuclei are produced
Each has 1 of each chromosome

30. Cytokinesis Not part of Meiosis II Occurs at the end of Meiosis II
Cells divide

32. Result of Meiosis II and Cytokinesis
4 genetically different haploid cells
All contain some chromosomes from mother and some from father
Each contains 1 of each chromosomes
No Sister Chromatids

33. Comparing mitosis vs. meiosis
Animation:
_view0/chapter2/animation__comparison_of_meiosis_and_ mitosis__quiz_1_.html