1. Biology
Meiosis

2. Remember from Chapter 1: CHARACTERISTICS OF LIVING THINGS ALL LIVING THINGS __________
REPRODUCE

3. Remember from Chapter 7, there are basically 2 types of cells__________ and ____________
EUKARYOTIC
PROKARYOTIC

4. Now let’s review Ch 10.......... Mitotic Cell Division
Mitosis makes two identical daughter cells from one Parent cell
Bacteria and other prokaryotes may use mitosis to reproduce – called Binary Fission
This is asexual reproduction

5. ASEXUAL REPRODUCTION Bacteria reproduce using This is mitosis!
BINARY FISSION
This is mitosis!

6. Regeneration is another way some animals reproduce asexually (mitosis)
Budding is used by plants and some animals to reproduce asexually (mitosis)
Hydra
Regeneration is another way some animals reproduce asexually (mitosis)
Planaria

7. MITOSIS Produces cells that are __________ copies of parent cell
identical

8. Major Events in Mitosis

9. Chromosome number must be maintained in animals.
Many plants have more than two copies of each chromosome.

10. Mitosis and meiosis are types of nuclear division that make different types of cells.
Mitosis makes more diploid cells.

11. MITOSIS-in conclusion2
Makes ___ cells genetically _________ to parent cell & to each other
Makes _________ cells
Makes __________
Used by organisms to: increase size of organism, repair injuries, and replace worn out cells
identical
2n (diploid)
SOMATIC (body)

12. ADVANTAGES OF ASEXUAL REPRODUCTION
Can make offspring faster
Don’t need a partner

13. ADVANTAGES OF ASEXUAL REPRODUCTION
Works great for making new skin cells, blood cells, and any of the other body cells that need to be replaced
Our body cells are called Somatic cells (repeat word)

14. DISVANTAGES OF ASEXUAL REPRODUCTION
ALL ALIKE
No genetic diversity within a population
One disease can wipe out whole population

15. Question….if not asexual, then how can we reproduce?

16. Sexual Reproduction
Sexual reproduction is when two gametes (sex cells) fuse together to make a zygote.

17. SEXUAL REPRODUCTION
In humans, (and in many other organisms), sexual reproduction combines the genetic material from the gametes of 2 parents (sperm & egg) into a zygote
-develops into offspring that are genetically __________ from parents
DIFFERENT

18. Let’s review sexual reproduction
In sexual reproduction, there are two parents.
Each parent has a gamete, or sex cell to donate to the offspring.
Each gamete has one set of chromosomes.
The two gametes come together (fertilization) to form one new cell called a Zygote.
This Zygote will grow and divide to become a unique organism.

19. ADVANTAGES OF SEXUAL REPRODUCTION
Allows for variation in population
Individuals can be different
Provides foundation for EVOLUTION
Allow species adapt to
changes in
their environment

20. EGG +
SPERM 
If egg and sperm cells had the same number of chromosomes as other body cells . . .
baby would have too many chromosomes!

21. MEIOSIS is the way we can avoid this problem.
Meisosis makes cells with half the number of chromosomes
for sexual
reproduction

22. Sex Cells (also called germ cells)
Germ cells develop into_ gametes.
Germ cells are located in the ovaries and testes of humans and other animals.
Gametes are sex cells:__________.
Gametes have DNA that is passed to the offspring.
egg and sperm
sex cells
(sperm)
(egg)

23. Haploid (n) cells have one copy of every chromosome
Haploid (n) cells have one copy of every chromosome.(Remember diploid cells have two copies)
Gametes are haploid.
Human gametes have 22 autosomes and 1 sex chromosome.

24. Haploid cells develop into mature gametes.
Gametogenesis is the production of gametes.
Gametogenesis differs between females and males.
Sperm become streamlined and motile.
Sperm primarily contribute DNA to an embryo.

25. Haploid cells develop into mature gametes.
Gametogenesis differs between females and males.
Eggs contribute DNA, cytoplasm, and organelles to an embryo.
During meiosis, the egg gets most of the contents; the other cells form polar bodies.

26. KEY CONCEPT Gametes have half the number of chromosomes that body cells have.

27. DIPLOID & HAPLOID HOMOLOGOUS CHROMOSOMES
Most cells have 2 copies of each chromosome = ______________
(one from mom; one from dad)
All BODY (___________) cells are diploid
DIPLOID 2n
HOMOLOGOUS CHROMOSOMES
SOMATIC

28. HOMOLOGOUS Chromosomes
SAME SIZE
SAME SHAPE
CARRY GENES for the SAME TRAITS
BUT ______________!
(Don’t have to have the SAME CHOICES)
NOT IDENTICAL

29. DIPLOID & HAPLOID
Some cells have only one copy of each chromosome = _____________
Fertilization between egg and sperm occurs in sexual reproduction.
All gametes (sperm and
egg) cells are haploid
HAPLOID 1n

30. SO……what is a chromosome?
main organelle involved in the Cell Cycle
Found in the nucleus
Contains genetic material (DNA)
Has 2 major parts-a centromere and sister chromatids

31. There are two types of Chromosomes.
Your body cells have 23 pairs of chromosomes.
Homologous pairs of chromosomes have the same structure.
For each homologous pair, one chromosome comes from each parent.

32. There are two types of Chromosomes.
Chromosome pairs 1-22 are autosomes.
Sex chromosomes, X and Y, determine gender in mammals.

33. Humans have 46 chromosomes (23 pair)
Cats have 38 chromosomes (19 pair)
Chickens have 78 chromosomes (39 pair)
Horses have 64 chromosomes (32 Pair)
Potatoes have 48 chromosomes (24 pair)
Goldfish have100 chromosomes (50 pair)
Fruit fly has 8 (4 pair)
Corn has 20 (10 pair)
Peas have 14 (7 pair)
Mosquitoes have 6 chromosomes (3 pair)
Mice have 40 chromosomes (20 pair)
Elephants have 56 chromosomes (28)

34. So Again……
The zygote of humans have 23 pairs of chromosomes (or 46 individual chromosomes)
23 chromosomes come from each parent
= 46
Humans have 46 chromosomes

35. The process of Meiosis- The Formation of Sex Cells

36. Meiosis makes haploid cells from diploid cells.
Meiosis occurs in sex cells.
Meiosis produces gametes.

37. I. Introduction to Meiosis
A. Purpose - to make sex cells for reproduction.
B. Why can’t mitosis do this?
Remember….mitosis would make too many chromosomes.

38. MEIOSIS 4 1n Germ cells OR Gametes (sperm & eggs) sexual reproduction
Makes ____ cells genetically different from parent cell & from each other
Makes _____ cells
Makes ______________
Used for ____________ 1n
Germ cells
OR Gametes (sperm & eggs)
sexual reproduction

39. WHAT MAKES MEIOSIS DIFFERENT ?
Crossing Over, Segregation, and Independent Assortment
ALL are ways MEIOSIS results in
=______________________________
So daughter cells are ______________
from parents and from each other
GENETIC RECOMBINATION
different

40. WHAT MAKES MEIOSIS DIFFERENT ?
Homologous chromosomes pair up during ________________
= ______________
PROPHASE I
SYNAPSIS
This group of FOUR (4)
chromatids is called a
_________________
TETRAD

41. WHAT MAKES MEIOSIS DIFFERENT?
1. Exchange of DNA between homologous pairs = _____________ during PROPHASE I
CROSSING OVER
Separates gene choices and Allows shuffling of genetic material

42. CROSSING OVER rearranging of DNA Allows for_________________
in different combinations
After crossing over, chromatid arms are________________ anymore
NOT IDENTICAL

43. WHAT MAKES MEIOSIS DIFFERENT ?
Separation during ANAPHASE I
-chromosome pairs separate
SEGREGATION & INDEPENDENT ASSORTMENT

44. SEGREGATION & CROSSING OVER together make even more combinations

45. INDEPENDENT ASSORTMENT

46. INDEPENDENT ASSORTMENT at ANAPHASE I
Lots of different combinations are possible!
This is why you don’t look exactly like your brothers and sisters even
though you share the same parents!

47. SO WHAT MAKES MEIOSIS DIFFERENT ?
SYNAPSIS & CROSSING OVER (PROPHASE I)
2. SEGREGATION & INDEPENDENT ASSORTMENT in Anaphase I create genetic recombination
3. Skip INTERPHASE II (NO S) CELL DIVIDES TWICE, BUT… ONLY COPIES DNA ONCE

48. WHAT MAKES MEIOSIS DIFFERENT ?
3. Skip INTERPHASE II (No S)
CELL DIVIDES TWICE, BUT …
ONLY COPIES ITS DNA ONCE
MITOSIS: G1 S G2 P M A T C       
MEIOSIS:
( I ) G1 A T C S G2 P M        P M A T C
( II )    

49. Workings of Meiosis
A. Meiosis is - the formation of sex cells (eggs and sperm)
1. Gametes - another name for sex cells.
A. Gametes have haploid chromosome number

50. B. Meiosis is the making of eggs and sperm with half the number of chromosomes as the parent cell.
1. Female egg = 23
2. Male sperm = 23

51. C. Two Main Stages of Meiosis
1. Meiosis I
a. Prophase I
b. Metaphase I
c. Anaphase I
d. Telophase I

52. 2. Meiosis II
a. Prophase II
b. Metaphase II
c. Anaphase II
d. Telophase II
D. There is only one interphase

53. Cells go through two rounds of division in meiosis.
Meiosis reduces chromosome number and creates genetic diversity.

54. Meiosis I and meiosis II each have four phases, similar to those in mitosis.
Pairs of homologous chromosomes separate in meiosis I.
Homologous chromosomes are similar but not identical.
Sister chromatids divide in meiosis II.
Sister chromatids are copies of the same chromosome.
homologous chromosomes
sister
chromatids
sister
chromatids

55. Meiosis I occurs after DNA has been replicated.
Meiosis I divides homologous chromosomes in four phases.

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

57. Meiosis I A. Interphase 1. Replication of chromosomes occurs.
2. This is the only interphase.

58. B. Prophase I
1. Chromatids appear
2. Centrioles split.
3. Centrioles move to the opposite poles.
4. Spindle fibers appear

59. 5. Nucleolus disappears
6. Nuclear membrane disappears
7. Tetrads form - two pairs of homologous chromosomes joining together.

60. 8. Crossing-over occurs here - genes are exchanged between homologous chromsomes.
a. Creates variation in new offspring

61. C. Metaphase I
1. Tetrads line up at the equator.

62. D. Anaphase I
1. Tetrads separate.
2. Chromatids are pulled to the opposite poles.

63. E. Telophase I
1. Chromatids still visible.
2. Nucleolus and Nuclear Membrane reforms.
3. Centrioles replicate
4. Two new cells.

64. IV. Meiosis II A. No interphase begins this phase.
1. 2 cells with the haploid chromosome number begin this stage.
2. Meiosis II will always have two cells in each phase.

65. B. Prophase II
1. Nuclear membrane and nucleolus disappear.
2. Centrioles split
3. Centrioles move to the poles.

66. 4. Spindle fibers form.
5. Chromatids are visible and attach to spindle fibers.

67. C. Metaphase II
1. Chromatids line up on the equator.

68. D. Anaphase II
1. Centromeres separate.
2. Chromotids are pulled to opposite poles.

69. E. Telophase II
1. Centrioles replicate
2. Nuclear membrane and nucleolus reappear.
3. Spindle fibers disappear.

70. 4. 4 new cells are formed
a. Only have half the number of chromosomes as the parent cell.
b. Males - all 4 remain alive and viable.
c. Females – one egg grows rest (polar bodies) die off.

71. V. Meiosis-Mitosis Comparison
A. Mitosis
1. 4 phases
2. Produces 2 diploid cells
3. Daughter cells identical to parent

72. B. Meiosis
1. 8 phases
2. 4 haploid cells produced
3. Daughter cells not identical to parent
4. Contain tetrads and crossing-over.

73. 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.

74. Figure Meiosis
Section 11-4
Meiosis I

75. Figure Meiosis
Section 11-4
Meiosis I
Meiosis I

76. Figure Meiosis
Section 11-4
Meiosis I
Meiosis I

77. Figure Meiosis
Section 11-4
Meiosis I

78. Figure Meiosis
Section 11-4
Meiosis I

79. Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.

80. Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.

81. Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.

82. Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.

83. Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.

84. That’s All For Now Folks!