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. Asexual Reproduction
Single parent
All offspring genetically identical

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

6. Homologous Chromosomes Carry Different Alleles
Chromosomes in homologous pairs
One maternal, one paternal
May carry different alleles

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

8. Sexual Reproduction Shuffles Alleles
Offspring inherit new combinations of alleles, produces variations in traits
This variation is the basis for evolutionary change

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

11. Meiosis: Two Divisions
Two consecutive nuclear divisions
Meiosis I
Meiosis II
DNA not replicated between divisions
4 haploid nuclei form

12. 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

13. 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

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

15. Effect of Crossing Over
Crossing over mixes maternal and paternal segments
Creates new allele combinations

16. 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)

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

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

19. 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

20. 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

21. Fig , p.163

22. Fertilization Haploid Male and female gametes unite - nuclei fuse
Produces diploid nucleus in zygote
Which 2 gametes unite random - adding to variation

23. 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

24. Factors Contributing to Variation among Offspring
Crossing over
Random alignment of chromosomes at meiosis I
Random combination of gametes at fertilization

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

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

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

28. Crossing Over… a preview taken from Chapter 11

29. Linkage Groups Genes on one type of chromosome travel together
Degree of linkage may vary

30. Full Linkage A B a b x Parents: A B a b AB ab F1 offspring: All AaBb
meiosis, gamete formation
Equal ratios of two types of gametes: A B a b
Figure Page 178
50% AB
50% ab

31. Incomplete Linkage AC ac A C a c x Parents: A C a c F1 offspring:
All AaCc
meiosis, gamete formation A a A a
Unequal ratios of four types of gametes: C c c C
parental
genotypes
recombinant
genotypes
Figure Page 178

32. Crossover Frequency Proportional to the distance that separates genesB C D
Crossing over will disrupt linkage between A and B more often than C and D
In-text figure Page 178

33. Linkage Mapping in Humans
Linkage maps based on pedigree analysis through generations
Color blindness and hemophilia are very closely linked on X chromosome