1. MEIOSIS

2. Meiosis
The form of cell division by which gametes, with half the number of chromosomes, are produced.
Diploid (2n)  haploid (n)
Involves two divisions:
meiosis I
meiosis II

3. Meiosis Sex cells divide to produce gametes
sperm or
egg
Gametes have half the # of chromosomes.

4. Meiosis Occurs only in gonads (testes or ovaries).
Processes:
Male: spermatogenesis
-making of sperm
Female: oogenesis
-making of eggs
Meiosis is similar to mitosis with some chromosomal differences.

5. Spermatogenesis n=23 n=23 2n=46 sperm haploid (n) meiosis II human
sex cell
diploid (2n)
n=23
meiosis I

6. Stages:
Interphase I
Meiosis I
Interphase II
Meiosis II

7. Interphase I Similar to mitosis interphase. DNA replicates in the
S phase
Each duplicated chromosome will eventually (prophase I) consist of two identical sister chromatids attached at their centromere.

8. Interphase I Nucleus and nucleolus are visible. chromatin
nuclear membrane
cell membrane
nucleolus

9. Meiosis I (four phases)
a. prophase I
b. metaphase I
c. anaphase I
d. telophase I

10. Prophase I Longest and most complex phase (90%).
Homologous chromosomes come together to form a tetrad.
Tetrad is two chromosomes or four chromatids total.
One of the chromosomes comes from Mom and one from Dad

11. Prophase I
Homologous chromosomes
sister chromatids
Tetrad

12. Prophase I
Chromosomes condense.
Tetrads form.

13. Metaphase I Shortest phase Tetrads align on the equator.
Chromosomes are lined up with their homologue.

14. Metaphase I INDEPENDENT ASSORTMENT OCCURS:
Orientation of homologous pairs (to poles) is random.
In the tetrad, Mom’s chromosome could be on the left or the right with Dad’s on the other side.
Leads to Genetic Variation

15. Metaphase I

16. Metaphase I Independent Assortment:
Humans have 46 chromosomes or 23 pairs of chromosomes.
Since each pair lines up randomly from every other pair, there are 8 million different combinations of the 23 pairs!!!

17. Anaphase I Homologous chromosomes separate and move towards the poles.
Sister chromatids remain attached at their centromeres.

19. Telophase I Each pole now has haploid set of replicated chromosomes.
BUT the chromosomes still consist of two chromatids.

21. Meiosis II Very short interphase II –
no more DNA replication
The next set of cell divisions will separate the chromatids.
Meiosis II is similar to mitosis. Can you figure out how?

22. Meiosis II (four phases)
a. prophase II
b. metaphase II
c. anaphase II
d. telophase II

23. Prophase II same as prophase in mitosis (Hint: you already
Know this picture!
But now BOTH cells
go on together…)

24. Metaphase II same as metaphase in mitosis
The chromosomes line up at the equator

26. Anaphase II same as anaphase in mitosis
The chromatids separate at their centromeres and move towards the opposite poles

27. Telophase II Same as telophase in mitosis. Nuclei form.
Four haploid daughter cells produced.

29. Meiosis n=2 n=2 2n=4 sperm haploid (n) meiosis II meiosis I sex cell
diploid (2n)

30. The End Product of Meiosis
From one cell in the gonads (testes or ovary), 4 new cells will be formed.
Each of the new cells will contain only one member from each homologous pair.
Either the chromosome from Mom or Dad but NOT both!!!---Haploid!

31. Question: 10 chromosomes (haploid)
A cell containing 20 chromosomes (diploid) at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?
10 chromosomes (haploid)

32. Question:
A cell containing 40 chromatids at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?
10 chromosomes

33. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
# of Chromosomes in the end
How they line up on the equator
Replication of DNA
Separation of Chromosomes during Anaphase
End Product
Haploid vs Diploid

34. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Replication of DNA
Separation of Chromosomes during Anaphase
End Product
Haploid vs Diploid

35. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Replication of DNA
Separation of Chromosomes during Anaphase
End Product
Haploid vs Diploid

36. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Replication of DNA
Separation of Chromosomes during Anaphase
End Product
Haploid vs Diploid

37. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Replication of DNA
Separation of Chromosomes during Anaphase
End Product
Haploid vs Diploid

38. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Replication of DNA
Separation of Chromosomes during Anaphase
End Product
Haploid vs Diploid

39. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome (double stranded)
# of Chromosomes in the end
1 of each kind of chromosome
1 of each kind of chromosome (single stranded)
How they line up on the equator
Replication of DNA
Separation of Chromosomes during Anaphase
End Product
Haploid vs Diploid

40. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 kind of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Individually
Replication of DNA
Separation of Chromosomes during Anaphase
End Product
Haploid vs Diploid

41. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Individually
In homologous pairs tetrads
Replication of DNA
Separation of Chromosomes during Anaphase
End Product
Haploid vs Diploid

42. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Individually
In homologous pairs tetrads
Replication of DNA
Separation of Chromosomes during Anaphase
End Product
Haploid vs Diploid

43. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Individually
In homologous pairs tetrads
Replication of DNA
S phase of interphase
Separation of Chromosomes during Anaphase
End Product
Haploid vs Diploid

44. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Individually
In homologous pairs tetrads
Replication of DNA
S phase of interphase
S phase of interphase I
Separation of Chromosomes during Anaphase
End Product
Haploid vs Diploid

45. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Individually
In homologous pairs tetrads
Replication of DNA
S phase of interphase
S phase of interphase I
No replication in interphase II
Separation of Chromosomes during Anaphase
End Product
Haploid vs Diploid

46. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Individually
In homologous pairs tetrads
Replication of DNA
S phase of interphase
S phase of interphase I
No replication in interphase II
Separation of Chromosomes during Anaphase
Separate 2 chromatids at the centromere
End Product
Haploid vs Diploid

47. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Individually
In homologous pairs tetrads
Replication of DNA
S phase of interphase
S phase of interphase I
No replication in interphase II
Separation of Chromosomes during Anaphase
Separate 2 chromatids at the centromere
Separate Homologous Pairs
End Product
Haploid vs Diploid

48. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Individually
In homologous pairs tetrads
Replication of DNA
S phase of interphase
S phase of interphase I
No replication in interphase II
Separation of Chromosomes during Anaphase
Separate 2 chromatids at the centromere
Separate Homologous Pairs
End Product
Haploid vs Diploid

49. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Individually
In homologous pairs tetrads
Replication of DNA
S phase of interphase
S phase of interphase I
No replication in interphase II
Separation of Chromosomes during Anaphase
Separate 2 chromatids at the centromere
Separate Homologous Pairs
End Product
Somatic Cell (2 identical cells)
Haploid vs Diploid

50. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Individually
In homologous pairs tetrads
Replication of DNA
S phase of interphase
S phase of interphase I
No replication in interphase II
Separation of Chromosomes during Anaphase
Separate 2 chromatids at the centromere
Separate Homologous Pairs
End Product
Somatic Cell
Not Done Yet
Haploid vs Diploid

51. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Individually
In homologous pairs tetrads
Replication of DNA
S phase of interphase
S phase of interphase I
No replication in interphase II
Separation of Chromosomes during Anaphase
Separate 2 chromatids at the centromere
Separate Homologous Pairs
End Product
Somatic Cell
Not Done Yet
Gamete
Haploid vs Diploid

52. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Individually
In homologous pairs tetrads
Replication of DNA
S phase of interphase
S phase of interphase I
No replication in interphase II
Separation of Chromosomes during Anaphase
Separate 2 chromatids at the centromere
Separate Homologous Pairs
End Product
Somatic Cell
Not Done Yet
Gamete
Haploid vs Diploid
Diploid

53. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Individually
In homologous pairs tetrads
Replication of DNA
S phase of interphase
S phase of interphase I
No replication in interphase II
Separation of Chromosomes during Anaphase
Separate 2 chromatids at the centromere
Separate Homologous Pairs
End Product
Somatic Cell
Not Done Yet
Gamete
Haploid vs Diploid
Diploid
Haploid

54. Comparing Mitosis and Meiosis
Characteristic
Mitosis
Meiosis I
Meiosis II
# of Chromosomes in the beginning
2 of each kind of chromosome
1 of each kind of chromosome
# of Chromosomes in the end
How they line up on the equator
Individually
In homologous pairs tetrads
Replication of DNA
S phase of interphase
S phase of interphase I
No replication in interphase II
Separation of Chromosomes during Anaphase
Separate 2 chromatids at the centromere
Separate Homologous Pairs
End Product
Somatic Cell
Not Done Yet
Gamete
Haploid vs Diploid
Diploid
Haploid