1. ANNOUNCEMENTS
LAB #3 MITOSIS & MEIOSIS has been moved to FRIDAY because I’m not finished grading lab #1.
DO THE SAMPLE FREE RESPONSE QUESTIONS FOR HOMEWORK. I’ll post them on facebook and teacherweb.
Do the lab bench exercise for LAB 3 mitosis & meiosis
LAB 3 is now on FRIDAY- you will have a lab quiz
Here are other websites that will help you:
TEST #2 IS TUESDAY 10/9… YOUR BIG CHANCE TO BRING YOUR GRADE WAY UP! :)

2. Meiosis & Sexual Life Cycles
CHAPTER 13
Meiosis & Sexual Life Cycles

3. Asexual reproduction produces clones ex. Hydra sea sponge

4. ASEXUAL REPRODUCTION reproduction which does not involve meiosis, reduction, or fertilization.
Only one parent is involved in asexual reproduction.
A lack of sexual reproduction is relatively rare among multicellular organisms, for reasons that are not completely understood.
Current hypotheses suggest that asexual
reproduction may have short term benefits
when rapid population growth is
important or in stable environments,
while sexual reproduction offers a net
advantage by allowing more rapid
generation of genetic diversity, allowing
adaptation to changing environments.
Types of asexual reproduction
1.1 Binary fission
1.2 Budding
1.3 Vegetative reproduction
1.4 Spore formation
1.5 Fragmentation
1.6 Parthenogenesis
1.7 Agamogenesis

5. Figure 13.x1 SEM of sea urchin sperm fertilizing egg
Sexual reproduction
= genetic recombination
= diversity
= better chance of survival
Sexual reproduction offers
a net advantage by allowing
more rapid generation of
genetic diversity, allowing
adaptation to changing
environments.

6. WHY SEX?
Natural selection operates on populations through the phenotypic differences (traits) that individuals display; meiosis followed by fertilization provides a spectrum of possible phenotypes on which natural selection acts, and variation contributes to the long-term continuation of species.

7. Figure 13.4 The human life cycle
Fertilization involves the fusion of two gametes, increases genetic variation in populations by providing for new combinations of genetic information in the zygote, and restores the diploid number of chromosomes.
Meiosis ensures that each gamete (sperm/egg) receives one complete haploid (1n) set of chromosomes.

8. Figure 13.x3 Human female karyotype shown by bright field G-banding of chromosomes

9. Figure 13.x5 Human male karyotype shown by bright field G-banding of chromosomes

10. QUIZ: What determines whether you are genetically male or female?
What are autosomes?
What are gametes?
What is a zygote?
What is the difference between a diploid cell and haploid cell?
What is Meiosis?
Sex chromosome combo XX=female XY=male.
Non-sex chromosomes (1-22)
Sex cells- sperm or egg.
Fertilized egg.
Diploid=2n (homologous chromosomes); hapliod=1n (only one of each kind of chromosome)
Nuclear division that includes a “reduction” it reduces the chromosome number by 1/2.

11. The creation of gametes for sexual
reproduction (MEIOSIS)
Occurs in 2 stages:
MEIOSIS I- REDUCTION
separates homologous chromosomes.
2n ---> 1n
ex > 23
split up the “pairs” or TETRAD
Law of Segregation- alleles of a gene
Separate during gamete formation.
MEIOSIS II
separates sister chromatids
1n (2 chromatids) --->
2 separate x 1n chromosomes
*similar to mitosis.

12. Figure 13.7 The stages of meiotic cell division: Meiosis I

13. meiosis1 is like separating all the pairs of shoes in your closet… putting one of each kind in one room & the other in another room.
During meiosis, homologous chromosomes are paired, with one homologue originating from the maternal parent and the other from the paternal parent. Orientation of the chromosome pairs is random with respect to the cell poles.
Separation of the homologous chromosomes ensures that each gamete receives a haploid (1n) set of chromosomes composed of both maternal and paternal chromosomes.

14. Figure 13.7 The stages of meiotic cell division: Meiosis II

15. Major Differences between Mitosis & Meiosis: (2 divisions- not 1 creates 4 haploid cells- not 2 diploid)
PROPHASE IS SPECIAL…
In Prophase 1 of Meiosis 1
the homologous chromosomes
line up together.
2. SYNAPSIS is the process of
pairing homologous
chromosomes.
3. TETRAD is 4 chromatids of
a homologous pair.
4. CHIASMATA are the X shaped
regions of chromatid overlap.
5. CROSSING OVER produces
recombinant chromosomes
when pieces break off & attach.

16. During meiosis, homologous chromatids exchange genetic material via a process called “crossing over,” which increases genetic variation in the resultant gametes.
Benefit to the organism’s species because it produces genetic variation.
Recombinant chromosomes are produced.
New combinations of your parent’s genes in your gametes.
Diversity = better chances for survival of a species.
CROSSING OVER

17. Figure 13.7 The stages of meiotic cell division: Meiosis I

18. INTERPHASE I Cell grows by producing proteins (cyclin) and organelles
Chromosomes replicate
Centrosomes/centrioles replicate
Preparation for cell division

19. PROPHASE I Chromatin condenses
Homologous replicated chromosomes line up together
“SYNAPSIS”
Crossing over occurs
TETRAD consists of 4 chromatids
CHIASMA(TA)

20. METAPHASE I
Spindle microtubules from opposite poles attach to one each of a homologous pair of replicated chromosomes.
Homologous pairs poised to move to opposite poles of the cell.
Position of pairs on metaphase plate leads to variation due to independent assortment.
=Alleles of different genes assort independently during gamete formation.

21. Figure The results of alternative arrangements of two homologous chromosome pairs on the metaphase plate in meiosis I

22. Independent Assortment
means that when you separate these pairs it doesn’t matter if one side gets the left or right shoe. Each pair is split up independently.
How many ways could you split up these 12 pairs?
2 n (n=#chromosomes)
2 12 =
For humans???? =

23. ANAPHASE I Homologous pairs of chromosomes are separated.
Sister chromatids remain attached at their centromere.
Independent assortment occurs now… the separation of each chromosome pair occurs independently.

24. Figure The results of alternative arrangements of two homologous chromosome pairs on the metaphase plate in meiosis I

25. TELOPHASE I Cytokinesis occurs. 2 haploid daughter cells are formed.
Each chromosome still consists of 2 sister chromatids.
Meiosis II is next.
(INTERKINESIS)

26. Figure 13.7 The stages of meiotic cell division: Meiosis II

27. MEIOSIS II Essentially mitosis
Begins with haploid cells (unlike mitosis which starts with diploid cells)
Sister chromatids pulled apart
Results in 4 haploid cells.
Each with one set of chromosomes.

28. Figure 13.8 A comparison of mitosis and meiosis

29. SPERMATOGENESIS
Sperm are produced in the seminiferous tubules of the testes of adult males.
Each ejaculation contains million sperm cells. They live 4 days.
Each diploid stem cell (spermatogonium) produces 4 haploid sperm cells (spermatozoa)

30. OOGENESIS
DIFFERENCES BETWEEN OOGENSIS & SPERMATOGENESIS:
Cytokinesis is unequal- almost all the cytoplasm is taken by a single daughter cell SECONDARY OOCYTE. This cell can go on to form the ovum (egg).The other smaller cells are Polar bodies.
At birth, ovary already contains all the primary oocytes.
Oogenesis has long resting periods. Starting at puberty, a single primary oocyte completes meiosis I each month. The secondary oocyte completes meiosis II only if a sperm cell enters it.
* Ootid is an undifferentiated ovum.

32. THE PLANTS Alternation of Generations Sporophytes Spores Haploid
Gametophytes
Mitosis
There aren’t homologous chromosomes to separate by meiosis (already haploid)
DIPLOID
HAPLOID

33. Figure 13.8 A comparison of mitosis and meiosis: summary

34. Figure 13.5 Three sexual life cycles differing in the timing of meiosis and fertilization (syngamy)