Chapter 8 Cell Reproduction

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Chapter 8 Cell Reproduction
http//www.pisgahscience.com/bioonline/
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• Which of these pictures shows an organism with
  cell division taking
• place?

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I. Introduction - Cell Division

• Occurs more often in young, growing organisms or
  when damaged tissue is repaired.
• Some tissues like skin intestinal cell grow
  throughout life while some- like nerve cells, do
  not divide again after full size achieved.
• Genetic information must be divided between
  cells.
• How does this happen?

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Cell Division Reproduction

• -allows for growth reproduction of individuals
• -passes on genetic information to future
  generations.

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In this chapter

• Chromosome Structure
• Tightly coiled DNA molecules
• Cell Division-
• Mitosis (nuclear division)
• Cytokinesis (division of cytoplasm)
• Cell Reproduction-
• Meiosis- Process reduces of chromosomes to half
  of original cell to produce gametes.

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II. Chromosome Structure

• Chromosomes are rod-shaped structures made of DNA
  wrapped around a protein called HISTONE

HISTONE PROTEIN
DNA strand
http//www.firedbydesign.com/1949/cell-animation/
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Chromosome Structure

• When a cell is NOT dividing, the DNA is loosely
  coiled in the cell NUCLEUS is called CHROMATIN.

When eukaryotic cells are ready to divide, the
DNA coils tightly around proteins called
HISTONES forms CHROMOSOMES.
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Chromosomes

• Consist of 2 identical halves
• Each half is called a CHROMATID.
• Are attached to each other at the CENTROMERE.

http//www.micro.utexas.edu/courses/levin/bio304/g
enetics/chromosome.gif
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http//www.gla.ac.uk/cancerpathology/genemech/awes
t/chromatin.jpg
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Chromosome Structure
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How many Chromosomes in an Organism?

• Look at this table- Does the of chromosomes
  show how complex the organism is?..........NO!

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B. Chromosome Numbers In various species

• Adders Tongue Fern 1,262
• Carrot 18
• Cat 32
• Chimpanzee 48
• Human 46
• Dog 78
• Potato 48
• Earthworm 36
• Fruit fly 8
• Garden pea 20
• Lettuce 18
• Can different organisms can have same
  chromosomes? .. YES.
• Can any conclusion about relatedness be made
  because of this? NO.

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• Sex chromosomes or Autosomes.
• Sex Chromosomes (X, Y) - determine sex carry
  genes for other characteristics.
• Autosomes- all of the other chromosomes in an
  organism.
• Example Humans have 2 sex chromosomes
  remaining 44 are autosomes. Humans have 46
  chromosomes!

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Sex chromosomes

• Females are XX
• Males are XY
• Males determine the sex of the baby- the sperm
  may contain either an X or a Y eggs can only
  have Xs.

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Homologous Chromosomes

• Most organisms have 2 copies of each chromosome.
• These pairs are called homologous chromosomes or
  homologues.

geneticsmodules.duhs.duke.edu/Design/page.asp...
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2 copies of each gene

• On each homologue- there are a genes for the same
  traits
• For Example
• if one of the homologous chromosomes has a gene
  for eye color, so will the other.

http//course1.winona.edu/sberg/ILLUST/homolog1.gi
f
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Homologous chromosomes

• The 2 chromatids
• are exact copies of each other- theyre
  identical.
• attached by a centromere.
• The Homologous chromosomes
• ARE NOT exact copies.
• (One set is from mom, one from dad)
• They have genes for the same traits

www.emunix.emich.edu
The large red blue chromosomes are
homologous. The small purple green chromosomes
are homologous.
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Homologous chromosomes in humans
www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?bookg...
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Karyotype

• A picture (photomicrograph) of chromosomes.
• Notice that humans have 46 chromosomes
• 22 homologous pairs of autosomes
• Plus 2 sex chromosomes. (Is this person male or
  female?)

Karyotype Copied from http//homepages.uel.ac.uk/
V.K.Sieber/human.htm
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A human karyotype
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Diploid Haploid cells

• Diploid- cells having 2 sets of chromosomes.
• Haploid- have only 1 set of chromosomes
• These are Sperm cells Egg cells.
• What is the number of chromosomes in a human
  haploid cell? (23)

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• Diploid is usually abbreviated 2n
• ( where n is the number of chromosomes in that
  organism)
• (in humans, the diploid- or 2n number is 46
• Haploid is 1n.
• When an egg cell (1n) combines with a sperm cell
  (1n), the new cell will be diploid (2n)
• What would happen if haploid cells were not
  used in sexual reproduction?

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III. Cell Division

• Prokaryotic Cell Division
• Prokaryotes are bacteria that lack nuclei
  membrane bound organelles.
• Have a single circular stand of DNA
• molecule is not coiled do not form chromosomes.
• Division is much simpler than in eukaryotic cells
• Binary fission - how prokaryotic cells divide.

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• Binary fission
• - Is the division of a prokaryotic cell into 2
  identical offspring cells. (creates clones)

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Cell Reproduction Mitosis Meiosis

• B. 2 kinds of cell division in eukaryotic cells
• Mitosis occurs in cells for
• growth, development, repair
• or asexual reproduction.
• Meiosis occurs during formation of gametes for
  sexual reproduction

www.ccs.k12.in.us/.../Humanembryology.htm
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2. The Cell Cycle

• The cell cycle is the repeating set of events in
  the life of a cell. 2 main parts further
  divided
• INTERPHASE Time between cell divisions
• G1 phase
• S phase
• G2 phase
• CELL DIVISION- When chromosomes cytoplasm are
  equally divided.
• Mitosis - nuclear division
• Cytokinesis - cytoplasm division

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http//137.222.110.150/calnet/cellbio/page6.htm
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3 Stages of Interphase

• G1 phase- cell grows to mature size.
• G1 stands for the time gap
• after cell division before DNA replication.
• S phase- cells DNA is copied (synthesized).
• (S stands for synthesize, meaning to make)
• G2 phase- the cell prepares for cell division.
• G2 is the time gap between DNA synthesis cell
  division.
• Some cells Exit the cell cycle
• Go phase- state where cells do not copy DNA or
  prepare for cell division. (example- CNS cells)

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C. Mitosis

• - is division of the nucleus
• results in
• two offspring cells
• Diploid chromosomes
• genetically identical (clones) of the
  original cell.

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Stages of Mitosis

• A process divided into 4 phases
• 1. PROPHASE
• 2. METAPHASE
• 3. ANAPHASE
• TELOPHASE
• Memory aids "People Meet And Talk", or "PMAT"
• or Pro met Anna (on the)
  telophone
• or make up your own!

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What happens during each phase of mitosis?

• PROPHASE-
• - coiling of DNA into chromosomes.
• -The nucleus starts to disappear.
• -Centrosomes appear (In animal cells -centrioles
  appear also) move to opposite poles of the
  cell.
• -Spindle fibers, made of microtubules, radiate
  from the centrosomes forms the mitotic spindle
  will be used to equally divide the chromosomes
  in the next phase.

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1. Prophase

• Can you list some things that happen in prophase?
• Find the structures in
• the drawing
• Nuclear membrane
• Homologous Chromsomes
• Chromatids
• Centromere
• Centrosomes
• Spindle fibers (look in
• book for 2 types of spindle fibers.)

Drawings from www.tqnyc.org
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2. METAPHASE

• chromosomes are moved to the center of the cell
• Note how they line up.
• Chromosomes are easiest to ID under a microscope
  during metaphase -most karyotypes are made from
  cells in metaphase.

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3. ANAPHASE

• - the chromatids separate at the centromere
  move
• to opposite poles.
• - after they separate,
• each chromatid is now considered to be a
• separate chromosome.
• (Tricky question- what n is a cell in
  anaphase? 4 )

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4. TELOPHASE

• After the chromosomes reach the opposite ends of
  the cell
• the spindle fibers disassemble,
• the chromosomes return to a less tightly coiled
  state,
• the nuclear envelope reforms in each newly
  forming cell.

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http//jabberwiki.wikispaces.com/file/view/mitosis
1.gif/53565174
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D. Cytokinesis

• Division of the cytoplasm
• In animal cells- a cleavage furrow forms as the
  area of the cell membrane pinches the cell into
  2.
• In plant cells- a cell plate forms a new cell
  wall as vesicles from the golgi apparatus join
  together at the midline of the 2 dividing cells.

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E. Control of Cell Division

• A cell spends most of its time in interphase.
• What triggers a cell to leave interphase
  divide?
• feedback from Checkpoints
• 1. Cell growth checkpoint (G1)- if the cell is
  healthy grows to mature size, protiens will
  intiate DNA synthesis.
• 2. DNA synthesis checkpoint (G2) proteins check
  results of DNA replication , signal OK
• 3. Mitosis checkpoint, if ok- growth cycle
  starts.

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Cell Division Errors

• If mutations occur
• proteins may not function properly
• growth may not be controlled
• When control is lost cancer.

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IV. Meiosis

• How it is different than mitosis
• reduces the number of chromosomes in new cells to
  half the number in the original cell.
• Produces four haploid cells (gametes)
• Different than two diploid cells as in mitosis.

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Beginning meiosis

• Cells begin meiosis just like they begin mitosis,
  after interphase.
• Cells must divide twice to reduce the number of
  chromosomes so we have Meiosis I Meiosis II.
• Remember- the whole point of meiosis is to make
  gametes (which are 1N)

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A. Meiosis- 8 phases

• MEIOSIS I
• 1. PROPHASE I
• 2. METAPHASE I
• 3. ANAPHASE I
• 4. TELOPHASE I
• MEIOSIS II
• 5. PROPHASE II
• 6. METAPHASE II
• 7. ANAPHASE II
• 8. TELOPHASE II

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MEIOSIS I -what happens in each phase?

• PROPHASE I
• -Spindle fibers appear the nuclear membrane
  disappears as in mitosis.
• NOTE IN MEIOSIS I -HOMOLOGUES LINE UP NEXT TO
  EACH OTHER.
• -This pairing of homologous chromosomes, which
  does NOT occur in mitosis, is a synapsis.
• -Each pair of homologous chromosomes is a
  tetrad.

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Genetic Recombination

• During synapsis, chromatids within a pair of
  homologues may twist around each other.
• Parts of the chromatids may break off attach on
  the homologous chromosome.
• This is called crossing-over.
• Crossing over permits exchange of genetic
  materials
• genetic recombination.

• http//regentsprep.org/Regents/biology/units/evolu
  tion/crossovr.gif

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Important to understand

• Crossing-over,
• which is when portions of homologous chromosomes
  line up to form tetrads in synapsis.
• exchange genetic material,
• occurs during prophase I
• results in genetic recombination.

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• 2. METAPHASE I
• Pairs of homologous chromosomes (tetrads) line up
  on metaphase plate.
• 3. ANAPHASE I
• Tetrads split- reducing the cells to haploid
• The chromosomes have randomly separated- this is
  called Independent Assortment.
• 4. TELOPHASE I
• 2 new cells begin to split off. Cytokinesis
  occurs.

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MEIOSIS II

• Meiosis II occurs in both cells made in meiosis I
• 5. PROPHASE II- Chromosomes condense, nuclear
  membrane breaks down, spindle fibers form.  NOT
  preceded by replication or recombination.
• 6. METAPHASE II- Chromosomes line up on
  metaphase plate
• 7. ANAPHASE II- The chromosomes divide at the
  centromeres
• 8. TELOPHASE II- Chromosomes begin to uncoil,
  nuclear envelope reforms, followed by
  cytokinesis.

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Stages of Meiosis, continued
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• Pictures from http//www.agry.purdue.edu/courses/
  agry

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• The biggest differences between mitosis meiosis
  occur at
• prophase I (Meiosis I has synapsis, tetrads
  crossing-over. Mitosis does not.)
• metaphase I (Meiosis I has tetrads lining up on
  metaphase plate.)
• anaphase I (Meiosis the centromeres do not
  separate haploid number chromosomes results.

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animation

• Biologygmh.com
• http//glencoe.mcgraw-hill.com/sites/0078695104/st
  udent_view0/unit3/chapter10/concepts_in_motion.htm
  l

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B. What are Gametes?

• Gametes are 1N cells for sexual reproduction
• Meiosis -occurs to form haploid gametes for
  sexual reproduction.
• - Spermatogenesis (production of sperm)
• -occurs in humans in testes
• -forms 4 haploid spermatids (develops 4
  sperm cells)
• - Oogenesis (produces 1 egg cell, 3 polar
  bodies)
• - All of the cytoplasm goes to 1 egg cell
• - 3 useless polar bodies are formed from the
  other nuclei they eventually disintegrate.

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Meiosis in Male and Female Animals
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Sexual reproduction

• is the formation of offspring through meiosis and
  the union of a sperm and an egg.
• Offspring produced by sexual reproduction are
  genetically different from the parents

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Questions

• Which of the following statements about
  prokaryotic chromosomes is true?
• A. Prokaryotes have at least two chromosomes.
• B. Prokaryotic chromosomes consist of a circular
  DNA molecule.
• C. Prokaryotic chromosomes include histone and
  nonhistone proteins.
• D. Prokaryotic chromosomes are made of DNA
  wrapped tightly around histone proteins.

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• 2. Crossing-over occurs during which process?
• A. mitosis
• B. meiosis I
• C. meiosis II
• D. interphase

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• 3. Which type of cell division is shown in the
  diagram?
• A. mitosis
• B. meiosis
• C. binary fission
• D. sexual reproduction

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• 4. What are the differences between mitosis
  meiosis?
• 5. Explains the difference between cytokinesis
  in plant animal cells.

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Your body contains over 200 different cell types!

• Cells are specialized into different types.
• The adult human body is made up of about 60-90
  trillion cells. That's a lot of cells!!!
• If you lined up all the cells in a human body
  end-to-end, you could actually circle the earth
  41/2 times!

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Stem cells

• Tissue precursor cells that have the ability to
  self-renew and differentiate into more specific
  cell types.
• They are important because they can replace
  dying, old or damaged cells.
• These cells are found in human embryos, fetuses,
  children and adults, i.e. at all stages of
  development and in most tissues but it is the
  embryonic cells which have raised the most
  controversy.

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• Early human embryos (5 - 6 day old blastocysts)
  have an outer cell layer from which the placenta
  develops, and an inner cell mass, in the region
  of 200 cells, which gives rise to the fetus. This
  inner cell mass is the source of embryonic stem
  cells.

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Growing stem cells is making clones of those
cells.

• Mixed reactions to the prospect of cloning for
  biomedical research.
• Supported by some for its medical promise
• Opposed by others who view it as intentional
  exploitation and destruction of human life
  created specifically for research purposes.
• Bioethical problems-

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A mere speck nestled in the eye of a needle, a
five-day-old embryo (photographed using an
electron microscope) contains controversial stem
cells. Photograph by Yorgos Nikas, M.D. Stem
cell research has been living up to its
reputation for being fast-paced. In the few
weeks since the July National Geographic cover
story went to press, several important advances
were reportedalong with some significant
political milestones.gtgt See Story from National
Geographic
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Stem cell research the US politics

• 2006- The Senate opens debate on bill that
  matches H.R. 810, which would ease Bush's
  restrictions. Matching bill passed the House May
  24, 2005. Senate also opens debate on two other
  stem cell bills. One would encourage research
  into creating stem cell lines without destroying
  human embryos and the other would ban the
  creation of a fetus solely for the purpose of
  destroying it and harvesting its body parts.
  President Bush says despite divided GOP, he will
  not ease policy and if passed will likely veto.
  Post Story
• 2006- In the first veto of his presidency, Bush
  vetoes the stem cell bill at a White House
  ceremony where he was joined by children produced
  by what he called "adopted" embryos. Post Story

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Embryonic stem cell advanceUpdated 734 p.m. ET
June 6, 2007http//www.msnbc.msn.com/id/19067616/

• Reprogrammed mouse cells avoid controversial
  destruction of embryos
• NEW YORK - In a leap forward for stem cell
  research, three independent teams of scientists
  reported Wednesday that they have produced the
  equivalent of embryonic stem cells in mice using
  skin cells without the controversial destruction
  of embryos.
• If the same could be done with human skin cells
  a big if the procedure could lead to
  breakthrough medical treatments without the
  contentious ethical and political debates
  surrounding the use of embryos.
• Experts were impressed by the achievement.

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Stay Tuned-

• Remember- science is a DYNANIC field- it keeps
  changing daily.

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Stem Cells Promise Difficulty

• -Read
• -page 160 (chapter 8 in Holt Textbook)
• -answer questions 1 ,2 3 with a partner
• - See reading assignment questions in packet
  handout.