1. Get 4 pipe cleaners in 4 different colors, with one pair being partners and the other pair being partners. 2. The document discusses cell division, including the two types of cell division - mitosis and meiosis. It provides details on the key stages and events of each. 3. Examples are given of mitosis (healing a wound) versus meiosis (fertilizing a lily). A practice with pipe cleaners to model chromosomes and cell division is described.

1. Please get
4 pipe cleaners
 in 4 different colors
One pair are partners
The other pair are partners

2. Cell DivisionCell Division

3. Cell DivisionCell Division
• 2 types:2 types:
• MitosisMitosis –– 1 body cell divides to1 body cell divides to
make 2 genetically identical bodymake 2 genetically identical body
cellscells

4. Cell DivisionCell Division
• MeiosisMeiosis –– 1 germ cell (in testes or1 germ cell (in testes or
ovaries) divides twice to make 4ovaries) divides twice to make 4
genetically different sex cellsgenetically different sex cells
• Sex cells =Sex cells = gametesgametes; sperm and; sperm and
ovaova

5. Quick CheckQuick Check
• A lily produces pollen that canA lily produces pollen that can
fertilize the ovule of another lily tofertilize the ovule of another lily to
make new lily plantsmake new lily plants
• What kind of cell division is this?What kind of cell division is this?

6. Quick CheckQuick Check
• Marcus got a paper cut in 1Marcus got a paper cut in 1stst
periodperiod
• By 5By 5thth
period he noticed that theperiod he noticed that the
wound had started to heal.wound had started to heal.
• What kind of cell division is this?What kind of cell division is this?

7. Homologous chromosomesHomologous chromosomes
• Each person has 2 of everyEach person has 2 of every
chromosomechromosome
– 1 from mom1 from mom
– 1 from dad1 from dad
• Together they are calledTogether they are called
homologous chromosomeshomologous chromosomes
– Same genes on themSame genes on them

8. MeiosisMeiosis
• Produces genetic diversityProduces genetic diversity
https://www.youtube.com/watch?v=JIUK2KSbvvI&t=22s

9. Key events in MeiosisKey events in Meiosis
1.1. Homologous chromosomesHomologous chromosomes
cross over each other andcross over each other and
swap piecesswap pieces

10. Key events in MeiosisKey events in Meiosis
2. Homologous chromosomes2. Homologous chromosomes
pair uppair up –– then separate to go tothen separate to go to
different cellsdifferent cells

11. Key events in MeiosisKey events in Meiosis
3. Each cell at the end of3. Each cell at the end of
meiosis contains only ½ themeiosis contains only ½ the
normal number ofnormal number of
chromosomes and each cell ischromosomes and each cell is
genetically uniquegenetically unique

12. Pipe Cleaner Chromosome
Practice

13. Directions
Cut each pipe cleaner in ½
Which two colors are going to be homologues?
Remember: homologous chromosomes are partner
chromosomes – not identical but nearly so.

14. One chromosome, that shows that the
DNA has been copied already.

15. A homologous pair of chromosomes

16. One sister chromatid

17. Centromere on a chromosome

18. 4 chromosomes after the DNA has been
copied

19. Step 1 of meiosis
Crossing over
between homologous
chromosomes occurs
Model it by cutting
your chromosomes

20. Let’s Practice with our pipe cleaners!
Set up Prophase 1
This is when crossing over will happen
Carefully cut off the end of one chromosome and
attach it to its homologous pair

21. Step 2 of Meiosis
Homologous chromosomes pair
up in the middle of the cell

22. Stage 3 of meiosis
Homologous chromosomes move to opposite ends of
the cell

23. Stage 4 of Meiosis
2 different cells

24. 2 different cells

25. 2 different cells

26. 4 different cells

27. Sexual ReproductionSexual Reproduction
• Sex cells divide by meiosisSex cells divide by meiosis toto
produceproduce haploid (n)haploid (n) gametesgametes

28. Sexual ReproductionSexual Reproduction
• Gametes will join & fertilizeGametes will join & fertilize
• Two gametes join to form aTwo gametes join to form a zygotezygote

29. SpermatogenesisSpermatogenesis
• Takes 8-9 weeks to completeTakes 8-9 weeks to complete

30. Sperm FormationSperm Formation

31. • A sperm is not a sperm UNTIL….A sperm is not a sperm UNTIL….
– It has a full flagellaIt has a full flagella
– Is motile (can move)Is motile (can move)

32. OogenesisOogenesis

33. Model with pipe cleanersModel with pipe cleaners
• Partner A: show the germ cell,Partner A: show the germ cell,
diploid number 4 in the first stagediploid number 4 in the first stage
of meiosisof meiosis
• Partner B: show the 4 haploid cellsPartner B: show the 4 haploid cells
(2 chromosomes) at the end of(2 chromosomes) at the end of
meiosismeiosis

34. Evolution of SexEvolution of Sex
• FromFrom asexualasexual --->--->
sexualsexual
• From externalFrom external
fertilization ---> internalfertilization ---> internal
fertilizationfertilization
• Simplest = “Simplest = “broadcastbroadcast
fertilization,fertilization,”” eggs andeggs and
sperm sent into thesperm sent into the
water, chance meetingwater, chance meeting

35. Evolution of SexEvolution of Sex
• Evolved to sperm released,Evolved to sperm released,
swim to female, enter andswim to female, enter and
fertilize; larva is released intofertilize; larva is released into
waterwater
• To eggs and sperm releasedTo eggs and sperm released
externally but right next toexternally but right next to
each other (in a nest)each other (in a nest)
• To internal fertilization,To internal fertilization,
fertilized egg released intofertilized egg released into
water (oviparous)water (oviparous)

36. Evolution of SexEvolution of Sex
• To internal fertilization, eggsTo internal fertilization, eggs
hatch inside, juvenilehatch inside, juvenile
released into waterreleased into water
(ovoviviparous)(ovoviviparous)
• Some newly-hatched sharksSome newly-hatched sharks
eat their unhatched siblingseat their unhatched siblings
in the womb:in the womb: “intrauterine“intrauterine
cannibalism”cannibalism”
• To internal fertilization, liveTo internal fertilization, live
birth (viviparous)birth (viviparous)

37. Evolution of SexEvolution of Sex
• Marsupials = bornMarsupials = born
undeveloped (as embryos),undeveloped (as embryos),
crawl into a pouch tocrawl into a pouch to
complete developmentcomplete development
• Placental mammals = heldPlacental mammals = held
full-term within the uterus.full-term within the uterus.
• From no care of young ---->From no care of young ---->
increased parental careincreased parental care
• From eggs ----> placentaFrom eggs ----> placenta
(embryo more protected in(embryo more protected in
mother)mother)

38. MeiosisMeiosis
II

39. Prophase IProphase I
• DNA replicationDNA replication
has alreadyhas already
occurredoccurred
• HomologousHomologous
chromosomeschromosomes
pairpair and formand form
tetradstetrads, joined, joined
at aat a chiasmatachiasmata

40. DNA Wrapping AroundDNA Wrapping Around
Proteins to Condense IntoProteins to Condense Into
ChromosomesChromosomes

41. tetradstetrads crosscross
over andover and
separate intoseparate into
individualindividual
chromosomeschromosomes
TetradTetrad

42. Prophase IProphase I
Each tetradEach tetrad
has twohas two
chromo-chromo-
somes &somes &
fourfour
chromatidschromatids

43. Metaphase IMetaphase I
• TetradsTetrads line upline up at metaphase plate.at metaphase plate.
• Orientation isOrientation is randomrandom
• 50-50 chance50-50 chance forfor
daughter cells to getdaughter cells to get
either mother's oreither mother's or
father's homologuefather's homologue

44. Anaphase IAnaphase I
• ChiasmataChiasmata separateseparate..
• Chromosomes moveChromosomes move to separateto separate
polespoles
• Daughter cells nowDaughter cells now
haploid (haploid (2323
chromosomes), butchromosomes), but
each chromosomeeach chromosome
hashas two chromatidstwo chromatids..
Crossed over X-
shaped chromosomes

45. Telophase ITelophase I
• Nuclear envelopes mayNuclear envelopes may reformreform, or, or
the cell may quickly start meiosis IIthe cell may quickly start meiosis II
• CytokinesisCytokinesis
– Analogous to mitosisAnalogous to mitosis
where two completewhere two complete
daughter cells form.daughter cells form.

46. Meiosis I ReviewMeiosis I Review

47. Meiosis IIMeiosis II
• Similar to mitosis:Similar to mitosis: no "S" phaseno "S" phase..

48. Meiosis IIMeiosis II
• ChromatidsChromatids no longer identicalno longer identical
• Meiosis II separates chromatidsMeiosis II separates chromatids
producingproducing two daughter cellstwo daughter cells eacheach
withwith 2323 chromosomes (haploid.)chromosomes (haploid.)

49. Comparing Meiosis & MitosisComparing Meiosis & Mitosis
MitosisMitosis
• HomologousHomologous
chromosomeschromosomes
independent ofindependent of
each othereach other
• identicalidentical daughterdaughter
cellscells
MeiosisMeiosis
• HomologousHomologous
chromosomeschromosomes pair,pair,
forming tetrads untilforming tetrads until
anaphase Ianaphase I
• daughter cellsdaughter cells
haploid, uniquehaploid, unique

50. Comparing Meiosis & MitosisComparing Meiosis & Mitosis
Genetic identity of progenyGenetic identity of progeny
MitosisMitosis
• IdenticalIdentical
daughter cellsdaughter cells
MeiosisMeiosis
• Daughter cells haveDaughter cells have
new assortment ofnew assortment of
parental chromosomesparental chromosomes
• ChromatidsChromatids notnot
identical; crossingidentical; crossing
overover

52. Meiosis ReviewMeiosis Review
What stage is this?
How can you tell?
A B

53. Meiosis ReviewMeiosis Review
What stage is this?
How can you tell?
A B

54. Meiosis ReviewMeiosis Review
What stage is this?
How can you tell?
A B

55. Meiosis ReviewMeiosis Review
What stage is this?
How can you tell?
A B

56. Meiosis ReviewMeiosis Review
What stage is this?
How can you tell?
A B

57. Meiosis ReviewMeiosis Review
What stage is this?
How can you tell?
A B