1. Meiosis and Sexual Reproduction
Chapter 10
Meiosis and Sexual Reproduction

2. Bozeman Video—Cell Cycle, Mitosis, & Meiosis

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

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

5. Sexual Reproduction Involves
Meiosis
Gamete production
Fertilization
Produces genetic variation among offspring

6. SOMATIC VS GAMETE CELLS

7. AUTOSOMES VS. SEX CHROMOSOMES

8. Homologous Chromosomes Carry Different Alleles
Cell has two of each chromosome
One chromosome in each pair from mother, other from father
Paternal and maternal chromosomes carry different alleles

9. Homologous Chromosomes
Fig. 10-2, p.156

10. 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

11. Gamete Formation Gametes are sex cells (sperm, eggs)
Arise from germ cells
ovaries
anther
testes
ovary
Figure 10-3 Page 156

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

13. Human Karyotype 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
XX (or XY)
Fig. 10-4, p.157

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

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

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

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

18. Prophase I Each duplicated chromosome pairs with homologue
Homologues swap segments(THIS IS KNOWN AS CROSSING OVER WHICH OCCURS AT A SITE CALLED THE CHIASMATA)
Each chromosome becomes attached to spindle
Longest phase of meiosis
Fig. 10-5, p. 158

19. Metaphase I Tetrads are aligned on the metaphase plate
Chromosomes are pushed and pulled into the middle of cell
The spindle is fully formed
Fig. 10-5, p. 158

20. Anaphase I Homologous chromosomes segregate to opposite poles
The sister chromatids remain attached
Fig. 10-5, p. 158

21. Telophase I The chromosomes arrive at opposite poles
Usually followed by cytoplasmic division
Interkinesis (reforming of the nuclear membrane)may occur before Meiosis II but no more DNA duplication
Fig. 10-5, p. 158

22. Prophase II
Microtubules attach to the kinetochores of the duplicated chromosomes
If interkinesis happened, the nuclear membrane redisappears
Fig. 10-5, p. 158

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

24. Anaphase II
Sister chromatids and their centromeres separate to become independent chromosomes at opposite poles of each cell
Fig. 10-5, p. 158

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

26. Metaphase I Prophase I Anaphase I Telophase I
spindle equator
one pair of homologous chromosomes
newly forming microtubules
Prophase I
Anaphase I
Telophase I
Meiosis I
Stepped Art
Fig. 10-5a, p.158

27. Anaphase II Telophase II Prophase II Metaphase II
Meiosis II
Stepped Art
Fig. 10-5b, p.159

28. Crossing Over Each chromosome becomes zippered to its homologue
All four chromatids are closely aligned
Nonsister chromosomes exchange segments

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

30. 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

31. Possible Chromosome Combinations
As a result of random alignment, the number of possible combinations of chromosomes in a gamete is: 2n (n is number of chromosome types)

32. Bozeman Video--Meiosis

33. ROLES OF MITOSIS/MEIOSIS IN LIFE CYCLES

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

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

36. FUNGAL AND ALGAL LIFE CYCLE

37. 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

38. Factors Contributing to Variation among Offspring
Crossing over during prophase I
Random alignment of chromosomes at metaphase I (AKA Law of Independent Assortment of Chromosomes)
Random combination of gametes at fertilization (1 in 8 million possible egg combinations x 1 in 8 million posssible sperm combinations = 1 in 64 trillion possible zygote
Natural Selection-increases frequency of reproductively favorable traits

39. 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

40. Bozeman –Mitosis/Meiosis Bead Simulation

41. 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

42. 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

43. Comparison of Mitosis and Meiosis

44. Meiosis Square Dance Video