POD

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POD

• Compare and contrast asexual and sexual
  reproduction.
• What do you think triggers cells to divide?
• Give reasoning for your predictions

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The structure of eukaryotic chromosomes
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The Relationship between Chromosomes, DNA and
Genes

• DNA deoxyribose nucleic acid
• macromolecule, carries genetic information
• A gene is a short section of DNA

http//www.hhmi.org/biointeractive/dna-packaging
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• DNA is tightly packed in the nucleus of every
  cell.
• DNA wraps around special proteins called histones
• which form loops of DNA called nucleosomes.
• These nucleosomes coil and stack together to form
  fibers called chromatin.
• Chromatin in turn forms larger loops and coils to
  form chromosomes.

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TERMS YOU NEED TO KNOW
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Structure of a Chromosome

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Chromosome Numbers

• Sex chromosomes - determine the sex of an
  organism
• Autosomes - All other chromosomes in an organism

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• Humans
• Somatic Cells (body cells) 46 chromosomes
• - 2 Sex chromosomes X or Y
• women have two X chromosomes, men have an X and a
  Y
• - 44 autosomes
• Gametes (Sex cells) 23 chromosomes
• - 1 sex chromosome
• - 22 autosomes

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Chromosome Numbers

• Haploid and diploid are terms referring to the
  number of sets of chromosomes in a cell.
• diploid cells (2n) - Somatic cells (body cells),
  contains two complete sets of chromosomes
• every organism has a characteristic diploid
  number
• haploid cells (n) - Gametes (sex cells) have only
  one complete set of chromosomes
• the length and number of chromosomes is unique to
  each species of organism.

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• Chromosome Number
• 18
• 32
• 48
• 78
• 36
• 94
• 18

• Organism
• Carrot
• Cat
• Chimpanzee
• Dog
• Earthworm
• Goldfish
• Lettuce

http//www.ncbi.nlm.nih.gov/mapview/
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• Mactching sets of chromosomes in a diploid cell
  are
• called homologous chromosomes. Both chromo in a
• homologous pair contain information that code the
  
• same trait (genes).
• Example of trait Eye color
• Are sex chromosomes homologous? Why or Why not?

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Cell Division and Reproduction
PBS How Cells divide http//www.pbs.org/wgbh/nov
a/baby/divide.html
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Prokaryotic chromosomes

• Lack nuclei
• DNA found in cytoplasm
• Most contain a single, circular DNA chromosome

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The Prokaryotic Cell CycleCell Division in
Prokaryotes/Asexual Reproduction

• BINARY FISSION is the division of a prokaryotic
  cell into 2 offspring cells. (asexual
  reproduction)
• The cell grows in size.
• DNA replication - The chromosome makes a copy of
  itself, resulting in two identical chromosomes
• Cytokinesis - The cell splits into two new
  cells.  Each new cell contains identical genetic
  information as the original cell

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A protozoan undergoes binary fission
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Eukaryotic Cell CycleThe stages of life of a cell

• Interphase
• Mitosis
• Cytokinesis

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Eukaryotic Cell Cycle
http//highered.mheducation.com/sites/9834092339/s
tudent_view0/chapter10/control_of_the_cell_cycle.h
tml
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Cell Division in Eukaryotes

• A cell typically goes through stages during its
  life, growing and developing before it divides
  into new cells.
• The cell cycle is the repeating events that make
  up the life of a cell

http//www.biologie.uni-hamburg.de/b-online/librar
y/cat-removed/u4aos1p2.htmlChromosomes
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Interphase

• Period of normal metabolic activity
• Carries on all usual functions
• Increases in size
• Synthesizes new proteins and organelles
• DNA Replication DNA is duplicated (copied)
• Reminder DNA exist as chromatin within the
  nucleus. Chromatin are thin uncoiled strands of
  DNA wrapped around a protein
• allows each new cell will have a complete copy of
  each chromosomes

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• The actual dividing of the cell consists of two
  steps
• Mitosis
• cytokinesis

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Mitosis

• The division of the Nucleus
• Process by which a nucleus divides into 2
  identical nuclei
• Mitosis produces two daughter cells that are
  identical to the parent cell.  If the parent cell
  is haploid (N), then the daughter cells will be
  haploid.   If the parent cell is diploid, the
  daughter cells will also be diploid. 
• N N
• 2N 2N
• This type of cell division allows multicellular
  organisms to grow and repair damaged tissue.

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4 phases of Mitosis
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Prophase

• the chromatin coils (condenses) to form visible
  chromosomes
• nucleolus and the nuclear membrane begin to
  disappear
• centrosomes (centrioles) appear
• Spindle fibers start to form
• Centrioles begin to move to opposite ends

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• The chromatin condensed into chromosomes
• each chromosome contains two identical halves
  called sister chromatids
• The constricted area of each chromatid is called
  a centromere

Centromere
Sister chromatids
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Metaphase

• chromosomes are moved to the center of the cell
  (equator) by the spindle fibers attached to the
  centromeres
• The two sister chromatids of each chromosome are
  attached to spindle fibers from opposite ends of
  the cell

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Anaphase

• The sister chromatids are separated from each
  other now considered to be individual
  chromosomes
• The centromeres of each chromosome are pulled by
  the spindle fibers toward the opposite ends
  (poles) of the cell

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Telophase

• after the chromosomes reach opposite ends of the
  cell, the spindle fibers breakdown
• the chromosomes return to less tightly coiled
  Chromatin
• new nuclear envelope begins to form around the
  chromosomes at each end of the cell
• End of mitosis

Nuclear envelopes reappear
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Cytokinesis

• The cell membrane begins to pinch the cell in two
  as cytokinesis begins
• the cytoplasm of a cell and its organelles are
  equally separated into two daughter cells
• Completes the process of cell division
• the new cells are now in interphase

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• Cytokinesis differs between plants and animals
• Plant cells have a rigid cell wall, so the plasma
  membrane does not pinch in.
• the material for the new cell wall is called the
  cell plate
• The cell plate and membranes gather and fuse
  along the equator, between two two nuclei forming
  two identical cells

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Results

• unicellular organisms remain as single cells
• in multicellular organisms, cell growth and
  reproduction result in groups of cells that work
  together as tissue to perform a specific function
• http//www.sumanasinc.com/webcontent/anisamples/ma
  jorsbiology/mitosis.html
• http//www.johnkyrk.com/mitosis.html
• http//www.biology.arizona.edu/Cell_bio/tutorials/
  cell_cycle/cells3.html
• http//biology.about.com/library/blmitosisanim.htm
  

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Normal Control of the Cell Cycle

• Proteins regulate the progress of cell division
• Occasionally, cells lose control of the cell
  cycle.
• uncontrolled dividing of cells can result from
  proteins not functioning properly
• cancer is a malignant growth resulting from
  uncontrolled cell division