1. Meiosis
Chapter 10

2. Sexual Reproduction Chromosomes are duplicated in germ cells
Germ cells undergo meiosis and cytoplasmic division
Cellular descendents of germ cells become gametes
Gametes meet at fertilization

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

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

5. 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

6. 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

7. Gamete Formation Gametes are sex cells (sperm, eggs)
Arise from germ cells
ovaries
anther
testes
ovary
Figure 10.2a Page 164

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

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

10. Meiosis I In-text figure Page 165 Each homologue in the
cell pairs with its partner,
then the partners
separate
In-text figure Page 165

11. Meiosis II
The two sister chromatids of each duplicated chromosome are separated from each other
two chromosomes
(unduplicated)
one chromosome
(duplicated)
In-text figure Page 165

12. Meiosis I - Stages Prophase I Metaphase I Anaphase I Telophase I
Figure 10.4
Page 167

13. Prophase I Each duplicated chromosome pairs with homologue
Homologues swap segments
Each chromosome becomes attached to spindle
Figure 10.4 Page 167

14. Metaphase I Chromosomes are pushed and pulled into the middle of cell
The spindle is fully formed
Figure 10.4 Page 167

15. Anaphase I Homologous chromosomes segregate
The sister chromatids remain attached
Figure 10.4 Page 167

16. Telophase I The chromosomes arrive at opposite poles
Usually followed by cytoplasmic division
Figure 10.4 Page 167

17. Prophase II
Microtubules attach to the kinetochores of the duplicated chromosomes
Figure 10.4
Page 167

18. Metaphase II
Duplicated chromosomes line up at the spindle equator, midway between the poles
Figure 10.4
Page 167

19. Anaphase II
Sister chromatids separate to become independent chromosomes
Figure 10.4
Page 167

20. Telophase II The chromosomes arrive at opposite ends of the cell
A nuclear envelope forms around each set of chromosomes
Four haploid cells
Figure 10.4
Page 167

21. Crossing Over Each chromosome becomes zippered to its homologue
All four chromatids are closely aligned
Nonsister chromosomes exchange segments
Figure 10.5 Page 168

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

23. 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

24. 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

25. 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)

26. Possible Chromosome Combinations1 2 3
Possible Chromosome Combinations or or or
Figure 10.6 Page 169

27. multicelled sporophyte multicelled gametophytes
Plant Life Cycle
multicelled sporophyte
mitosis
zygote
Diploid
fertilization
meiosis
Haploid
gametes
spores
multicelled gametophytes
mitosis
Figure 10.7 Page 170

28. Animal Life Cycle Figure 10.7 Page 170 multicelled body mitosis zygote
Diploid
fertilization
meiosis
Haploid
gametes
Figure 10.7 Page 170

29. 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 10.8 Page 171

30. Spermatogenesis Figure 10.9 Page 171 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 171

31. 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

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

33. 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

34. 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

35. 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

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