1. The Continuation of Life
Meiosis
The Continuation of Life

2. Meiosis: The Continuation of Life

3. Homologous Chromosomes
Paired chromosomes
One from each parent
Genes for same trait
Alleles
Same order on chromosome

4. Homologous Chromosomes

7. Diploid vs. Haploid Diploid 2n Haploid 1n
Cell that has TWO of each kind of chromosome (parent) 2n
Haploid
Cell that has ONE of each kind of chromosome 1n

8. 23pairs  46pairs  96pairs…etc.
Question
What would happen if Mitosis was the only way our cells could divide?
23pairs  46pairs  96pairs…etc.
We need a way to divide the Chromosome # in half! What is this called??
Meiosis!

9. Meiosis
Purpose –
make haploid cells
Gametes
Egg
Sperm
Form Zygote

10. Phases of Meiosis Meiosis I Prophase I Metaphase I Anaphase I
Telophase I
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
Cytokinesis

11. Prophase I Same as in Mitosis… But…
Homologous Chromosomes find each other
Synapsis
Tetrads

12. Prophase I
Synapsis
Crossing over occurs
Exchange of Genetic material

13. Crossing Over
Crossing Over and its products!

14. Metaphase I
Homologous pairs line up
Tetrads still together

15. Anaphase I
Homologous Chromosomes separate
Independent Assortment

16. Telophase I Just like Telophase in Mitosis Chromosomes unwind
Nuclear membrane forms

17. Meiosis II Just like Mitosis!! Meiosis II Prophase II Metaphase II
Anaphase II
Telophase II

18. Prophase II
Chromosomes appear
Centrioles migrate
Spindle fibers

19. Metaphase II
Chromosomes line up
Like mitosis

20. Anaphase II
Chromosomes separate like in mitosis
Move to ends of cell

21. Telophase II Nuclear membrane forms Chromatids unwind  Chromatin
Finally…Cytokinesis!

22. Products
From single diploid (2N)
 4 Haploid (1N)

25. Cellsalive!
Meiosis: An Interactive Animation
Web Lesson Meiosis

28. Mitosis vs. Meiosis

29. Gametes Why are some of the chromosomes different colors?
Crossing Over!

30. Variation Genetic Variation is provided by meiosis
Because of assortment 70 trillion possibilities
Crossing Over increases that number
Reason for great variety of people

31. Mistakes in Meiosis Nondisjunction Trisomy – 1 extra chromosome
the failure of homologous chromosomes to separate properly
Trisomy – 1 extra chromosome
Monosomy – 1 less chromosome
Polyploidy – extra set of all chromosomes

33. Trisomy Trisomy 21 Down’s Syndrome Flattened face Shorter than normal
Heart defects

34. Monosomy Usually lethal but, but not in… Turner’s Syndrome
Look at Karyotype
What is wrong here?

35. Turner’s Syndrome

36. Polyploidy Whole extra set of chromosomes Death – animal zygotes
(3n) or (4n)
Death – animal zygotes
Often occurs in plants
Bigger and Healthier

37. Phase? #1

48. Question
What separates during Meiosis I?
Homologous Chromosomes

49. Question
What type of cell results from meiosis I?
Haploid!

50. Question
What separates during Meiosis II?
Sister Chromatids

51. Questions?