1. PowerLecture: Chapter 10
Meiosis and Sexual Reproduction

2. What you should understand
The two types of reproduction.
Why each occur and how.
What is a gamete and how it is made
Difference between haploid and diploid and which type of cell they occur.
Why sexual reproduction increases variation within a species.

3. Impacts, Issues: Why Sex
Asexual reproduction is easier and faster
Sexual reproduction can be an alternative adaption in changing environments

4. Differences between types of reproduction

5. Asexual Reproduction Single parent produces offspring
All offspring are genetically identical to one another and to parent
Mitosis

6. Sexual Reproduction Involves
Meiosis
Gamete production (egg and sperm)
Fertilization
Produces genetic variation among offspring
Chromosomes are duplicated in germ cells

7. Germ cells undergo meiosis and cytoplasmic division
Cellular descendents of germ cells (sex cells) become gametes (egg and sperm)
Gametes meet at fertilization

8. Gamete Formation Gametes are sex cells Arise from germ cells
Sperm
eggs
Arise from germ cells
Some plants can have both parts
testes
ovaries
anther
ovary
Figure 10-3 Page 156

9. anther (where cells that give rise to male gametes originate)
FLOWERING PLANT
anther (where cells that give rise to male gametes originate)
ovules, inside an ovary (where cells that give rise to female gametes originate)
Fig. 10-3a, p.156

10. Recap of chromosomes

11. Homologous Chromosomes Carry Different Alleles
Cell has two of each chromosome (homologous)
One chromosome in each pair from mother, other from father
Paternal and maternal chromosomes carry different alleles
Alleles are different forms of a gene
Examples

12. Homologous Chromosomes
You get one from each parent you have 23 pairs of homologous chromosomes. They carry the same genes but not necessary the same form of the gene.
Fig. 10-2, p.156

13. Sexual Reproduction Shuffles Alleles
Through sexual reproduction, offspring inherit new combinations of alleles, which leads to variations in traits
This variation in traits is the basis for evolutionary change

14. Chromosome Number Sum total of chromosomes in a cell
Germ cells are diploid (2n)
Gametes are haploid (n)
Meiosis halves chromosome number

15. Human Karyotype Explanation1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
XX (or XY)
Human Karyotype Explanation
Fig. 10-4, p.157

16. What is meiosis?

17. Meiosis: Two Divisions overview
Two consecutive nuclear divisions
Meiosis I
Meiosis II
DNA is not duplicated between divisions
Four haploid nuclei form

18. Meiosis I Each homologue in the cell pairs with its partner,
then the partners
separate
p. 158

19. Meiosis II
The two sister chromatids of each duplicated chromosome are separated from each other
two chromosomes
(unduplicated)
one chromosome
(duplicated)
p. 158

20. What is the difference between meiosis I and meiosis II in regards to the chromosomes.

21. Meiosis I - Stages
Prophase I
Metaphase I
Anaphase I
Telophase I

22. Prophase I Each duplicated chromosome pairs with homologue
Homologues swap segments (crossing over)
Each chromosome becomes attached to spindle
Fig. 10-5, p. 158

23. Metaphase I Chromosomes are pushed and pulled into the middle of cell
The spindle is fully formed
Fig. 10-5, p. 158

24. Anaphase I Homologous chromosomes segregate
The sister chromatids remain attached
Fig. 10-5, p. 158

25. Telophase I The chromosomes arrive at opposite poles
Usually followed by cytoplasmic division
Fig. 10-5, p. 158

26. Prophase II
Microtubules attach to the kinetochores of the duplicated chromosomes
Fig. 10-5, p. 158

27. Metaphase II
Duplicated chromosomes line up at the spindle equator, midway between the poles
Fig. 10-5, p. 158

28. Anaphase II
Sister chromatids separate to become independent chromosomes
Fig. 10-5, p. 158

29. Telophase II The chromosomes arrive at opposite ends of the cell
A nuclear envelope forms around each set of chromosomes
Four haploid cells
Fig. 10-5, p. 158

30. Meiosis
Meiosis I and II

31. Meiosis
Meiosis step-by-step

32. Crossing Over Each chromosome becomes zippered to its homologue
All four chromatids are closely aligned
Non-sister chromosomes exchange segments (which contain genes)

33. Crossing Over paternal homologue maternal homologue Stepped Art
Fig. 10-6, p.160

34. Crossing Over a Both chromosomes shown here were duplicated during
interphase, before meiosis. When prophase I is under way, sister
chromatids of each chromosome are positioned so close together
that they look like a single thread.
Fig. 10-6a, p.160

35. Crossing Over
b Each chromosome becomes zippered to its homologue, so all four chromatids are tightly aligned. If the two sex chromosomes have different forms, such as X paired with Y, they still get zippered together, but only in a tiny region at their ends.
Fig. 10-6b, p.160

36. Crossing Over
c We show the pair of chromosomes as if they already condensed only to give you an idea of what goes on. They really are in a tightly aligned, threadlike form during prophase I.
d The intimate contact encourages one crossover (and usually more) to happen at various intervals along the length of nonsister chromatids.
e Nonsister chromatids exchange segments at the crossover sites. They continue to condense into thicker, rodlike forms. By the start of metaphase I, they will be unzippered from each other.
f Crossing over breaks up old combinations of alleles and puts new ones together in the cell’s pairs of homologous chromosomes.
Fig. 10-6c, p.160

37. Effect of Crossing Over
After crossing over, each chromosome contains both maternal and paternal segments
Creates new allele combinations in offspring

38. Random Alignment
During transition between prophase I and metaphase I, microtubules from spindle poles attach to kinetochores of chromosomes
Initial contacts between microtubules and chromosomes are random
What does this mean?

39. Random Alignment
Either the maternal or paternal member of a homologous pair can end up at either pole
The chromosomes in a gamete are a mix of chromosomes from the two parents

40. combinations possible
Possible Chromosome Combinations 1 2 3
combinations possible or or or
Fig. 10-7, p.161

41. combinations possible1 2 3
combinations possible
Alignment at
metaphase I or or or
Stepped Art
Fig. 10-7, p.161

42. Crossing Over
Crossing over

43. Plant Life Cycle sporophyte zygote diploid fertilization meiosis
haploid
gametes
spores
gametophytes
Fig. 10-8a, p.162

44. Animal Life Cycle multicelled body zygote diploid fertilization
meiosis
haploid
gametes
Fig. 10-8b, p.162

45. Animal Life Cycle
Random alignment

46. Oogenesis three polar bodies (haploid) first polar body (haploid)
oogonium (diploid)
primary oocyte (diploid)
secondary oocyte (haploid)
ovum (haploid)
Meiosis I,
Cytoplasmic Division
Meiosis II,
Cytoplasmic Division
Growth
Figure Page 163

47. Generalized life cycles
Oogenesis
Generalized life cycles

48. Spermatogenesis Figure 10-9 Page 163 spermato- gonium (diploid )
primary spermatocyte (diploid)
secondary spermatocytes (haploid)
sperm (mature, haploid male gametes)
spermatids
(haploid)
Spermatogenesis
Meiosis I,
Cytoplasmic Division
Meiosis II,
Cytoplasmic Division
Growth
cell differentiation, sperm formation
Figure 10-9 Page 163

49. Fig , p.163

50. Animal Egg Formation
Sperm formation

51. Animal Egg Formation
Egg formation

52. Fertilization Male and female gametes unite and nuclei fuse
Fusion of two haploid nuclei produces diploid nucleus in the zygote
Which two gametes unite is random
Adds to variation among offspring

53. Factors Contributing to Variation among Offspring
Crossing over during prophase I
Random alignment of chromosomes at metaphase I
Random combination of gametes at fertilization

54. Mitosis & Meiosis Compared
Functions
Asexual reproduction
Growth, repair
Occurs in somatic cells
Produces clones
Meiosis
Function
Sexual reproduction
Occurs in germ cells
Produces variable offspring

55. Each person of a pair take out a piece of paper and you will compare PMAT of mitosis to meiosis. Skip the T.
How many squares do you need to do this?
When you are done share with another pair.
When everyone is done we will compare answers

56. Prophase vs. Prophase I Prophase (Mitosis) Prophase I (Meiosis)
Homologous pairs do not interact with each other
Prophase I (Meiosis)
Homologous pairs become zippered together and crossing over occurs

57. Anaphase, Anaphase I, and Anaphase II
Anaphase I (Meiosis)
Homologous chromosomes separate from each other
Anaphase/Anaphase II (Mitosis/Meiosis)
Sister chromatids of a chromosome separate from each other

58. What are the over arching concepts for mitosis and meiosis?
Focus on number of cells produced, how they are produced and chromosome number.

59. Results of Mitosis and Meiosis
Two diploid cells produced
Each identical to parent
Meiosis
Four haploid cells produced
Differ from parent and one another

60. Results of Mitosis and Meiosis
Comparing mitosis and meiosis