1. AGENDA Do Now! Meiosis Notes Meiosis (Amoeba sisters)
Hands-on activity: Draw and Explain Meiosis
Quizizz.com: Quick Assessment on your understanding
Closure

2. Reminder!!!
You have Test on Unit 4 on Friday 3/1/19

3. Do Now! 1. What are the 4 stages of Mitosis in order?
2. What results from Mitosis cell division? OR What is the END PRODUCT of Mitosis cell division?
3. What type of cells are divided in mitosis?
4. Write down all you remember from the discussion on Introduction to Meiosis.

4. Meiosis Vocab Review

5. Type of cells
Somatic cells: also called body cells, make up most of your body tissues and organs.
Gametes: sex cells—ova, or eggs, in the female, and spermatozoa, or sperm cells, in the male. DNA in your gametes can be passed on to your children.

6. Homologous Chromosomes
two chromosomes—one inherited from the mother, one from the father—that have the same length, shape and size.

7. Autosomes and Sex chromosomes
Chromosome pairs 1 through 22 make up your autosomes, chromosomes.
Sex chromosomes 23rd pair chromosomes, directly control the development of sexual characteristics.
Humans have 2 sex chromosomes, X and Y.

8. Diploid and Haploid
Diploid (2n): means that a cell has two copies of each chromosome.
Haploid(n): means that a cell has only one copy of each chromosome.

9. Sexual reproduction
Sexual reproduction: involves the fusion of two gametes, resulting in offspring that are a genetic mixture of both parents.

10. Meiosis
Meiosis is a form of nuclear division that divides a diploid cell into haploid cells.
Occurs only in gonads (testes or ovaries)
Males: 4 sperm are made
Females: 1 ovum is made

11. Compare and Contrast

12. Description of Meiosis
Similar to Mitosis
2 Divisions:
Meiosis I
Meiosis II
End result – 4 genetically non- identical cells haploid (gametes)
Men = 4 sperm
Females = 1 egg

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

15. Fertilization n=23 egg 2n=46 zygote
The fusion of a sperm and egg to form a zygote.
A zygote is a fertilized egg. (diploid)
n=23
egg
sperm
n=23
2n=46
zygote

16. Haploid (n): cell that has only one copy of each chromosome.
Diploid (2n): cell that has two copies of each chromosome, one from an egg and one from a sperm

18. Homologous (same/structure) chromosomes
One from father – paternal One from mother - maternal

19. Gametogenesis
Gametogenesis is the production of gametes.

20. Crossing over during meiosis increases genetic diversity.
Crossing over is the exchange of chromosome segments between homologous chromosomes during prophase I of meiosis I.

21. Phases of Meiosis

22. Interphase G1, S, & G2 take place as in mitosis
Chromosomes are replicated during S phase (synthesis)

23. Prophase I DNA coils tightly. (Chromosomes condense)
Synapsis occurs: two homologous chromosomes come together to form a tetrad.
Tetrad is two chromosomes or four chromatids (sister and non-sister chromatids).
Homologous chromosomes pair up and crossing over may occur
Crossing over: the exchange of chromosomal segments between a pair of homologous chromosomes.
Nuclear membrane dissolves

24. Prophase I

25. Crossing over during meiosis increases genetic diversity.
Crossing over is the exchange of chromosome segments between homologous chromosomes during prophase I of meiosis I.

26. Prophase I - Synapsis
Homologous chromosomes
sister chromatids
Tetrad

27. Cross over in Meiosis

28. Crossing Over

29. Metaphase I Spindle fibers attach to the centromere of each chromosome
Each tetrad lines up at the equator of the cell

30. Anaphase I
Spindle fibers shorten and pull homologous chromosome pairs away from each other
Each pole ends up with a complete haploid set of chromosomes

31. Telophase I Nuclear membrane reforms around daughter nuclei
Each daughter nucleus has two sister chromatids for each chromosomes
Because of crossing-over, the sister chromatids are NOT identical

32. Prophase II
Nuclear membrane dissolves and new spindle fibers form

33. Metaphase II Spindle fibers bind to both sides of centromere
Sister chromatids align at the equator of the cell

34. Anaphase II Spindle fibers shrink
Sister chromatids are pulled apart to opposite ends of the cell

35. Telophase II & Cytokinesis
Nuclear membrane reforms around sets of daughter chromosomes
Cell undergoes cytokinesis
End result is 4 haploid cells

36. Non disjunction
When sister chromatids, or homologs fail to separate during cell division.

37. Non- Disjunction

39. Meiosis – mouse testes
Parent cell
1st division
2nd division
4 gametes

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

42. Differences in meiosis
In males:
4 mature sperm
Males begin to produce sperm after puberty, produced constantly until death; meiosis II occurs immediately after meiosis I
Much smaller than egg (60 microns)
May have X or Y chromosomes
Have flagella to move
In females:
1 mature egg, 3 polar bodies which break down
Women born with all eggs they will have, meiosis I occurs before birth, meiosis II occurs once a month
Much larger (100 microns)
Have all X chromosomes
Has no method of movement

44. Gamete production
Females have XX for last pair of chromosomes (23 pair)
Males have XY for last pair (23 pair)
Since all eggs are X, father determines the sex of the child since the sperm may be X or Y

45. Mitosis vs. Meiosis Cell Division Cell Type # Daughter Cells
# Chromosomes
Haploid or Diploid
MITOSIS
MEIOSIS

46. Closure/Bell Ringer
What type of cells are formed during meiosis?