1. Bell Work Pick up your answer sheet for today’s benchmark
Review complex inheritance for 15 minutes
Take benchmark (ONLY do #1-24)

2. Chapter 11.4 – 11.5
Meiosis
AP Movie—Ch 09: Meiosis [100 Greatest Discoveries]

3. Cell Division / Asexual Reproduction
Mitosis
produce cells with same information
identical daughter cells
exact copies
clones
same amount of DNA
same number of chromosomes
same genetic information
Aaaargh! I’m seeing multiples!
At least
we’re not Robert…
One of him is enough! 

4. Asexual reproduction Single-celled eukaryotes reproduce asexually
yeast
Paramecium
Amoeba
Simple multicellular eukaryotes reproduce asexually
Hydra
budding
What are the advantages of asexual reproduction?
What are the disadvantages?

5. binary fission in amoeba
budding in yeast
binary fission in amoeba

6. Sexual Reproduction / Fertilization
in sexual reproduction, a gamete from each parent fuses (called fertilization)
joining of egg + sperm
Do we make egg & sperm by mitosis?
NO!
What if we did, then…. 46 + 46 92
egg
sperm
Doesn’t work!

7. How do we make sperm & eggs?
Must reduce 46 chromosomes  23
must half the number of chromosomes
diploid (2n) to haploid (n) (meiosis) 23 46 23 46
egg
meiosis 23 46 23
fertilization
sperm

8. Human female karyotype
diploid = 2 copies 2n
Human female karyotype
46 chromosomes
23 pairs XX

9. diploid = 2 copies 2n
Human male karyotype
46 chromosomes
23 pairs XY

10. Meiosis: Production of Gametes
Alternating processes, alternating stages
chromosome number must be reduced
diploid  haploid
2n  n
humans: 46  23
meiosis reduces chromosome number
fertilization restores chromosome number
haploid  diploid
n  2n
AP Link—Ch 09: HaploidvDiploid

11. Differences across Kingdoms
Not all organisms use haploid & diploid stages in same way
which one is dominant (2n or n) differs
but still alternate between haploid & diploid
have to for sexual reproduction

12. Paired Chromosomes both chromosomes of a pair carry “matching” genes
control same inherited characters
homologous = same information
diploid 2n
2n = 4
homologous chromosomes
(after S-stage of interphase) double stranded homologous chromosomes

13. Sexual Reproduction: Fertilization
from Mom
- 1 copy
- haploid
- 1n
from Dad
- 2 copies
- diploid
- 2n

14. Making Gametes for the Next Generation
- 2 copies
- diploid
- 2n
Notice that
we’re
mixing things
up over here!
- 1 copy
- haploid
- 1n

15. Meiosis = Reduction Division
special cell division in sexually reproducing organisms
reduce 2n  1n
diploid  haploid
half
makes gametes
sperm, eggs
WARNING: Meiosis evolved from mitosis, so stages & “machinery” are similar but the processes are radically different. Do not confuse the two!

16. 2 Divisions of Meiosis DNA replication
1st division of meiosis separates homologous pairs
2nd division of meiosis separates sister chromatids

17. Preparing for meiosis 1st step of meiosis Duplication of DNA
Why bother?
meiosis evolved after mitosis
convenient to use “machinery” of mitosis
DNA replicated in S phase of interphase of MEIOSIS (just like in mitosis)
2n = 6
single
stranded
2n = 6
double
stranded
M1 prophase

18. Meiosis 1 1st division of meiosis separates homologous pairs synapsis
single
stranded
1st division of meiosis separates homologous pairs
2n = 4
double
stranded
prophase1
tetrad
synapsis
2n = 4
double
stranded
metaphase1
telophase1
1n = 2
double
stranded

19. Meiosis 2 2nd division of meiosis separates sister chromatids
double
stranded
prophase2
1n = 2
double
stranded
metaphase2
1n = 2
single
stranded
telophase2

20. Steps of Meiosis Meiosis 1 Meiosis 2 interphase prophase 1 metaphase 1
anaphase 1
telophase 1
Meiosis 2
prophase 2
metaphase 2
anaphase 2
telophase 2
1st division of meiosis separates homologous pairs
(2n  1n)
AP Link—Ch 09: Stages of Meiosis
2nd division of meiosis separates sister chromatids
(1n  1n)
JUST LIKE MITOSIS

21. Check out the
animations on-line!

22. Check out the
animations on-line!

23. Bell Work
What is the main difference between Meiosis I and Meiosis II?

24. Meiosis 1

25. Meiosis 2

26. Mitosis vs. Meiosis
AP Link—Ch 09: Mitosis vs. Meiosis

27. Mitosis vs. Meiosis Mitosis Meiosis 1 division
daughter cells genetically identical to parent cell
produces 2 cells
2n  2n
produces cells for growth & repair
no crossing over
Meiosis
2 divisions
daughter cells genetically different from parent
produces 4 cells
2n  1n
produces gametes
crossing over

28. What are the steps? Division One Division Two Interphase
Phases of Meiosis I
Prophase I
Metaphase I
Anaphase I
Telophase I
Cytokinesis
Interkinesis
Phases of Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
Division One
Division Two

30. Crossing Over During prophase 1
homologous pairs swap pieces of chromosome
sister chromatids intertwine
called “crossing over”
AP Link—Ch 09: Crossing Over_A
tetrad
synapsis

31. Why is crossing over so important?
Crossing over exchanges pieces of the chromatids. This will cause a new combination of alleles
This leads to genetic variation
Because the chromatids that are passed to the offspring may have a different combination of alleles than the original chromatids
This means that if a gamete that contains the newly combined chromatid is used to fertilize a zygote, then the baby will have a different combination of traits than the parent. = Variation!

32. Example: A = Can roll tongue, and a = cannot roll tongue
B = Freckles and b = no freckles
It is now possible for baby to be able to roll tongue and have NO freckles, which was never possible for original chromosomes

33. Crossing Over Involves 3 steps New combinations of traits cross over
breakage of DNA
re-fusing of DNA
New combinations of traits

34. Using Crossing Over For Genetic Maps
If there are two gene loci that are affected by a crossover event, can we determine how far apart these loci are on a chromosome? Can we determine the distance of one gene locus from the centrosome?
YES! STAY TUNED FOR LAB 10!
Involves 3 steps
cross over
breakage of DNA
re-fusing of DNA
New combinations of traits

35. Stages of Meiosis

36. Meiosis leads to Genetic Variation
Meiosis & crossing over introduce great genetic variation to a population
drives evolution
Consider the greater variation with 23 pairs of chromosomes = mixing and matching

37. new gametes made by offspring
The Value of Meiosis
Meiosis introduces genetic variation
gametes of offspring do not have same chromosomes as gametes from parents
genetic recombination
random assortment in humans produces 223 (8,388,608) different combinations
This does not even include new combos due to crossing over!
from Mom
from Dad
new gametes made by offspring

38. Random fertilization
Any 2 parents will produce a zygote with over 70 trillion (223 x 223) diploid combinations (of chromosomes!)

39. Sources of Genetic Variability
Genetic variability in sexual reproduction!
independent assortment
homologous chromosomes in Meiosis 1
crossing over
between homologous chromosomes in prophase 1
random fertilization
random ovum fertilized by a random sperm
AP Link—Ch 09: Random Chromosome Arrangement
metaphase1

40. Sexual Reproduction Creates Variability
Sexual reproduction allows us to maintain both genetic similarity & differences.
Michael & Kirk Douglas
Baldwin brothers
Martin & Charlie Sheen, Emilio Estevez

41. What do these charts mean?
Left AP Link—Ch 09: John Kyrk Meiosis
Right AP Link—Ch 09: Meiosis (TSOB)