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In This Lesson: Meiosis (Lesson 3 of 3). Today is Wednesday, November 13 th , 2013. Pre-Class: Briefly summarize the events of the five steps of mitosis/ cytokinesis : -Prophase -Metaphase -Anaphase - Telophase - Cytokinesis Expect the Bag of Evil!. Today’s Agenda.

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today is wednesday november 13 th 2013

In This Lesson:

Meiosis

(Lesson 3 of 3)

Today is Wednesday,November 13th, 2013

Pre-Class:

Briefly summarize the events of the five steps of mitosis/cytokinesis:

-Prophase

-Metaphase

-Anaphase

-Telophase

-Cytokinesis

Expect the Bag of Evil!

today s agenda
Today’s Agenda
  • Mitosis Gizmo
  • Labeling Mitosis [Quia]
  • Guided Notes?
  • Reproduction review
  • Meiosis
  • Meiosis Web Lesson
  • And maybe…I don’t know…something interesting and seemingly off-topic.
  • Where is this in my book?
    • Academic: P. 275 and following…
    • Honors: P. 137 and following…
cell division gizmo
Cell Division Gizmo
  • Now, we’re going to put our knowledge to the test with a gizmo from ExploreLearning.
    • Called Cell Division Gizmo.
    • Directions are on the accompanying Quia quiz called Cell Division Gizmo.
    • [Log-in Instructions]
  • When you are done, attempt the Quia quiz called Labeling Mitosis.
    • This one’s important!
labeling mitosis
Labeling Mitosis
  • Log-in to Quia and take the quiz entitled, “Labeling Mitosis.”
  • This is an excellent review tool and will be online for the remainder of the year.
  • Note: “Labeling Meiosis” is different, but will also be available all year long.
the transition
The Transition
  • Crash Course – Mitosis – Splitting Up is Complicated
kinds of reproduction
Kinds of Reproduction
  • Sexual
    • Calm down – it only means you need two individuals to “do it.”
  • Asexual
    • Only one individual.
    • Remember binary fission?
asexual reproduction
Asexual Reproduction
  • All DNA copied to offspring.
  • Offspring is (are) clone(s).
  • Kinds of asexual reproduction:
    • Binary Fission
    • Budding
    • Fragmentation
asexual reproduction1
Asexual Reproduction
  • The big disadvantage:
    • Little genetic diversity
      • Offspring are almost exactly like parents.
      • Problems are usually not “taken care of.”
sexual reproduction
Sexual Reproduction
  • Increases genetic diversity
    • DNA from Mom and Dad
      • (instead of just one of them)
  • Requires the use of gametes
    • In animals: sperm and ova (egg cells)
    • Different for other living things
meiosis
Meiosis
  • Meiosis is another process of cell division.
  • Sexual reproduction only.
    • Why?
  • Like Mitosis, except:
    • # of chromosomes is halved.
    • Two cell divisions.
meiosis specific names
Meiosis: Specific Names
  • Meiosis produces gametes.
  • There are specific terms for how meiosis works:
    • ♀: producing ova (eggs) from oocytes is called oogenesis.
      • Oocytes are cells that produce eggs.
    • ♂ : producing sperm from spermatocytes is called spermatogenesis.
      • Spermatocytes are cells that produce sperm.
meiosis1
Meiosis
  • Meiosis is NOT a cycle:

http://upload.wikimedia.org/wikipedia/commons/5/54/Meiosis_diagram.jpg

stages of meiosis
Stages of Meiosis
  • First stages – Meiosis I:
    • Prophase I
    • Metaphase I
    • Anaphase I
    • Telophase I
    • Cytokinesis
  • Second stages – Meiosis II
    • Prophase II
    • Metaphase II
    • Anaphase II
    • Telophase II
    • Cytokinesis
  • Important: Steps I and II are not the same!
meiosis2
Meiosis
  • Meiosis Idivides the starting diploid cell into two haploid daughter cells.
    • From 46 to 23, diploid to haploid – the reductive step.
  • Meiosis IIdivides the cells but keeps the chromosome number the same.
    • Process is just like mitosis but without the duplication beforehand.
    • From 23 to 23, haploid to haploid.
prophase i

46 Chromosomes

92 Chromatids

Prophase I
  • Chromatin condenses to X-shaped chromosomes.
  • Maternal/paternal chromosomes pair up to form tetrads (pair of X-shaped chromosomes, four chromatids).
  • Crossing over occurs.

http://www.regentsprep.org/regents/biology/units/reproduction/crossingover.gif

http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect16.htm

about crossing over
About crossing over…
  • Biology’s way of “shaking things up.”
  • Sections of chromosomes are exchanged with one another.
  • Increases genetic variability.
  • Side Notes:
    • The spot at which the chromatids cross is called the chiasma.
    • Crossing over occurs in a process called synapsis.

http://library.thinkquest.org/20465/meiosis.html

about tetrads
About tetrads…
  • A tetrad is a set of two X-shaped chromosomes next to one another.
  • Tetrads exist starting in Prophase I and are split apart in Anaphase I.

http://home.comcast.net/~mjmayhew42/Biology%20notes/meiosis%20notes_files/image005.gif

Tetrad

metaphase i

46 Chromosomes

92 Chromatids

Metaphase I
  • Tetrads line up in the middle of the cell.
    • Remember, these are pairs of X-shaped chromosomes.
    • Half the tetrad is from Mom, half is from Dad.

http://www.uic.edu/classes/bios/bios100/lecturesf04am/metaphase1m.jpg

http://www.sinauer.com/cooper/4e/micro/16/16-02_Meiosis-Metaphase1(NL-Large).jpg

compare metaphases
Compare Metaphases
  • Metaphase – Mitosis
  • Metaphase I - Meiosis
anaphase i

23 Chromosomes

46 Chromatids

on each side!

Anaphase I
  • Tetradspulled apart (stay as X-shaped chromosomes).
    • Important: The sister chromatids remain joined to one another.

http://biog-101-104.bio.cornell.edu/bioG101_104/tutorials/cell_division/lily_review_fs.html

compare anaphases
Compare Anaphases
  • Anaphase – Mitosis
  • Anaphase I - Meiosis
telophase i and cytokinesis

23 Chromosomes

46 Chromatidsin each cell!

Telophase I and Cytokinesis
  • Chromosomes gather at cell poles.
  • Cell divides.

http://biog-101-104.bio.cornell.edu/bioG101_104/tutorials/cell_division/lily_review_fs.html

summary of meiosis i in diagrams
Summary of Meiosis I in Diagrams

Prophase I

Metaphase I

Anaphase I

Telophase I

end results of meiosis i
End Results of Meiosis I
  • After meiosis I, we end up with two haploidcells.
  • Still not ready to be gametes.
    • Need one more division.
  • Time for Meiosis II
    • Booyah!
      • Not really.
meiosis ii
Meiosis II
  • Like Mitosis, except this time, we’re gonna end up getting haploid cells from haploid cells.
    • Remember, Meiosis is NOT a cycle.
  • The good news? Meiosis II is the same as Mitosis!
    • Samesies!
prophase ii

23 Chromosomes

46 Chromatidsin each cell!

Prophase II
  • [SAME AS MITOSIS]
  • Chromosomes start in the X-shape.
  • Nuclear envelope dissolves, spindle appears.

http://www.sinauer.com/cooper/4e/micro/16/16-05_Meiosis-Prophase2(NL-Large).jpg

metaphase ii

23 Chromosomes

46 Chromatidsin each cell!

Metaphase II
  • [SAME AS MITOSIS]
  • Chromosomes line up in the middle of the cell.

http://www.sinauer.com/cooper/4e/micro/16/16-06_Meiosis-Metaphase2(NL-Large).jpg

anaphase ii

23 Chromosomesin each cell!

Anaphase II
  • [SAME AS MITOSIS]
  • Chromosomes pulled apart at centromeres, move toward poles.
  • Chromosomes are no longer X-shaped.

http://www.sinauer.com/cooper/4e/micro/16/16-07_Meiosis-Anaphase2(NL-Large).jpg

telophase ii and cytokinesis

23 Chromosomes

in each cell!

TelophaseII and Cytokinesis
  • Nuclear envelope re-forms.
  • Cell divides.
  • Chromosomes return to chromatin.
  • 4 GENETICALLY DISTINCT haploid cells result!

http://www.sinauer.com/cooper/4e/micro/16/16-08_Meiosis-Telophase2(NL-Large).jpg

summary of meiosis i in diagrams1
Summary of Meiosis I in Diagrams

Prophase I

Metaphase I

Anaphase I

Telophase I

summary of meiosis ii in diagrams
Summary of Meiosis II in Diagrams

Prophase II

Metaphase II

Anaphase II

Telophase II

summary of mitosis in diagrams
Summary of Mitosis in Diagrams

Prophase

Metaphase

Anaphase

Telophase

the finished products
The Finished Products
  • After meiosis, here’s what’s left:
  • ♂: 4 sperm cells
  • ♀: 1 ovum, 3 polar bodies
    • Polar bodies are shriveled “non-eggs.”
      • In other words, meiosis in females results in only one viable egg.
    • Why polar bodies? To provide the egg enough cytoplasm to nourish the potential embryo.
    • Compare the size of sperm and egg:
      • http://learn.genetics.utah.edu/content/begin/cells/scale/
summary of mitosis
Summary of Mitosis

Start with one diploid cell that has 46 chromosomes.

End with two diploid daughter cells that each have 46 chromosomes.

46

Mitosis

(diploid to diploid)

46

46

summary of meiosis males
Summary of Meiosis (Males)

Start spermatogenesis with one diploid spermatocyte that has 46 chromosomes.

46

End with four haploid sperm cells that each have 23 chromosomes.

Meiosis I

(diploid to haploid)

23

23

Meiosis II

(haploid to haploid)

23

23

23

23

summary of meiosis females
Summary of Meiosis (Females)

Start oogenesiswith one diploid oocyte that has 46 chromosomes.

46

End with one haploid ovum with 23 chromosomes and three polar bodies.

Meiosis I

(diploid to haploid)

23

23

First polar body

Meiosis II

(haploid to haploid)

23

23

23

23

Second polar body

Second polar body

Second polar body

just like mitosis
Just like Mitosis?
  • Meiosis I is different from Mitosis:
    • Tetrads are pulled apart instead of X-shaped chromosomes.
    • Crossing over happens in Prophase I
      • Identical genes are not passed on.
  • Meiosis II is just like Mitosis except:
    • Chromosomes are not duplicated beforehand.
labeling meiosis
Labeling Meiosis
  • Visit Quia and try the quiz entitled Labeling Meiosis.
  • This is very similar to the Labeling Mitosis quiz and will also be on our Unit 4 Test.
  • We will do it as a class in a few moments…
aside reproductive strategies
Aside: Reproductive Strategies
  • In meiosis: Notice how males produce as much sperm as possible (at “low cost”), whereas females invest a lot into one cell.
  • In ecology/behavior: Notice how males (typically) attempt to pass their genes on by mating with as many individuals as possible with little parental “duties,” whereas females (as young bearers) invest their time in their single brood.
  • Sideside note: This explains why females’ menstrual cycles synchronize if they live in close proximity to one another.
time for an activity
Time for an Activity
  • The Meiosis Web Lesson!
    • Find those web lesson sheets.
  • Website is linked on my page:
    • http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meiosis.html
exit ticket
Exit Ticket
  • Which step of meiosis (I or II) reduces the number of chromosomes?
  • What is the purpose of “crossing over?”
  • You must turn this in or show me on your way out.
  • P.S. Yay the cell cycle is done!