stages of meiosis, what happens to chromosomes, spermatogenesis and oogenesis

1. Ch. 10 MeiosisCh. 10 Meiosis

2. What you need to knowWhat you need to know
and be able to doand be able to do
Essential KnowledgeEssential Knowledge
• In eukaryotes, heritable
information is passed
to the next generation
via processes that
include the cell cycle
and meiosis plus
fertilization.
• Biological systems
have multiple
processes that increase
genetic variation.
Learning ObjectiveLearning Objective
• The student is able to
compare and contrast
processes by which
genetic variation is
produced and
maintained in
organisms from
multiple domains

3. MeiosisMeiosis
• Chromosomes in aChromosomes in a diploiddiploid germgerm
cellcell segregate twice, producingsegregate twice, producing 44
haploidhaploid daughter cells calleddaughter cells called
gametesgametes
• ProducesProduces
geneticgenetic
diversitydiversity

4. Homologous chromosomesHomologous chromosomes
• The cell has two sets ofThe cell has two sets of
each chromosomeeach chromosome
– one is derived from theone is derived from the
mother and the othermother and the other
from the father.from the father.
– The maternal andThe maternal and
paternal chromosomes inpaternal chromosomes in
a homologous pair havea homologous pair have
the same genes at thethe same genes at the
same loci, but possiblysame loci, but possibly
different allelesdifferent alleles

5. MeiosisMeiosis
II

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

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

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

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

10. Draw prophase 1, diploidDraw prophase 1, diploid
number of 4number of 4

11. Prometaphase IPrometaphase I
• NuclearNuclear membrane disappearsmembrane disappears
• OneOne kinetochorekinetochore
formsforms perper
chromosomechromosome
• ChromosomesChromosomes
attached to spindleattached to spindle
fibers.fibers.
Place
where
spindle
fiber
attaches

12. 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

13. Draw metaphase 1Draw metaphase 1

14. 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

15. Draw anaphase 1Draw anaphase 1

16. 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.

17. Telophase 1 and cytokinesisTelophase 1 and cytokinesis

18. Meiosis I ReviewMeiosis I Review

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

20. 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.)

21. Prophase 2Prophase 2

22. Metaphase 2Metaphase 2

23. Anaphase 2Anaphase 2

24. Telophase 2Telophase 2

25. 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

26. 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

28. Sexual ReproductionSexual Reproduction
• Sex cells divide bySex cells divide by meiosismeiosis toto
produce haploid gametesproduce haploid gametes
• GametesGametes will join & fertilizewill join & fertilize
• Two gametes join to formTwo gametes join to form 11 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 fullIt has a full flagellaflagella
– IsIs motilemotile (can move)(can move)

32. OogenesisOogenesis

33. FertilizationFertilization
Meiosis II occurs AFTERMeiosis II occurs AFTER
sperm penetrationsperm penetration

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

35. Evolution of SexEvolution of Sex
• Evolved toEvolved to spermsperm released,released,
swimswim to female, enter andto female, enter and
fertilize; larva is released intofertilize; larva is released into
waterwater
• To eggs and sperm releasedTo eggs and sperm released
externallyexternally butbut right next toright next to
each othereach other (in a nest)(in a nest)
• ToTo internal fertilizationinternal fertilization,,
fertilized egg released intofertilized egg released into
water (water (oviparousoviparous))

36. Evolution of SexEvolution of Sex
• ToTo internal fertilizationinternal fertilization, eggs, eggs
hatch inside, juvenilehatch inside, juvenile
released into waterreleased into water
((ovoviviparousovoviviparous))
• 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 (birth (viviparousviviparous))

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

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

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

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

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

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

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