1. PowerLecture: Chapter 10
Meiosis and Sexual Reproduction

2. Why Sex
Fig. 10-1a, p.154

3. Why Sex
Fig. 10-1c, p.154

4. Germ cells undergo meiosis and cytoplasmic division
Cellular descendents of germ cells become gametes
Gametes meet at fertilization

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

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

7. 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

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

9. 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

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

11. 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

12. Chromosome Number Germ cells are diploid (2n) Gametes are haploid (n)
Meiosis halves chromosome number

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

14. PROPHASE I METAPHASE I ANAPHASE I TELOPHASE I
MEIOSIS I
newly forming microtubules in the cytoplasm
spindle equator (midway between the two poles)
one pair of homologous chromosomes
plasma membrane
PROPHASE I
METAPHASE I
ANAPHASE I
TELOPHASE I
Fig. 10-5, p.158

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

16. PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II
there is no DNA replication
between the two divisions
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II
MEIOSIS II
Fig. 10-5b, p.159

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

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

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

20. Possible Chromosome Combinations
As a result of random alignment, the number of possible combinations of chromosomes in a gamete is: 2n
(and this is without crossing over)

21. Possible Chromosome Combinations
2n for humans would be …
223 or…
8,388,608

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

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

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

25. 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

26. 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

27. Fig , p.163

28. 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 adding to variation

29. each chromosome duplicated during interphase
germ cell
germ cell
each chromosome duplicated during interphase n
MEIOSIS I
separation of homologues
MEIOSIS II
separation of sister chromatids
gametes
gametes 2n
diploid number restored at fertilization
zygote
Fig , p.166

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

31. An Ancestral Connection
Was sexual reproduction a giant evolutionary step from aseuxal reproduction?
Giardia intestinalis
Chlamydomonas