I. The Reproduction of Cells

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I. The Reproduction of Cells
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A. Why Do Cells Divide?

1. Repair- If cells are damaged, they must be
   replaced by cell division.
2. Replacement- If cells die, they must be replaced
3. Growth- If an organism is to increase in size,
   new cells must be added
4. Asexual Reproduction- one parent simply divides
   into two daughter cells

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B. Introduction to Eukaryotic Chromosomes

• Interphase, the eukaryotic nucleus contains
  Chromatin - long thin fibers of DNA and protein.
  The DNA can function when it is uncoiled but
  cannot be transported

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DNA Packing
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Introduction to Eukaryotic Chromosomes

• 2. For mitosis, the thin DNA fibers duplicate
  themselves and coil into structures called
  Chromosomes consisting of two highly coiled,
  exactly copied DNA strands called sister
  Chromatids which are held together by a structure
  called a centromere.

Centromere
Sister Chromatids
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C. The Cell Cycle
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1. Interphase- time preparing for the next
division

1. First Gap (G1) Organelles are produced
2. Synthesis (S) DNA replication occurs
3. Second Gap (G2)- cell grows to adult size

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2. Prophase

• Chromosomes shorten and thicken
• The nucleolus disappears
• Centrioles move to opposite ends of the cell
• Spindle fibers form
• Prometaphase nuclear membrane fragments
  and spindle fibers attach to chromsomes at the
  kinetochore

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3. Metaphase

• Spindle fibers made of microtubules align the
  chromosomes in the middle of the metaphase plate

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4. Anaphase

• Chromosomes are pulled by the spindle fibers to
  opposite ends of the cell

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Mechanism of Chromosome Movement in Anaphase
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5. Telophase Cytokinesis

1. Chromosomes become long and thin again
2. New Nuclear membrane and nucleolus form
3. Actin and Myosin fibers cause the cell membrane
   to pinch in

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Mechanisms of Cytokinesis The Division of the
Cytoplasm
Arrows indicate the contraction of actin fibers
separating the two daughter cells. Green
indicates the remains of spindle fibers
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1. Animal Cell Cytokinesis

• A cleavage furrow forms a shallow groove near the
  old metaphase plate.
• A contractile ring of actin microfilaments form
  and begin contracting until the cell pinched in
  two.
• The remains of the spindle breaks and
  phospholipid membranes fuse. The cells are
  separated.

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2. Plant Cytokinesis

1. Golgi vesicles containing cellulose, lignin and
   other building materials fuse near the old
   metaphase plate producing a cell plate
2. The plate grows laterally until they fuse with
   the cell wall separating the cells.

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Cancer- Uncontrolled Growth of Cells

1. Tumors interfere with the normal functioning of
   the organ.
2. Malignant Tumor keeps getting larger and will
   spread
3. Benign Tumor tends to stop growing
4. Metastasis- Cancer cells break off and spread to
   other parts of the body

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Warning Signs of Cancer

• Change in bowel or bladder habits. Blood in
  feces or urine
• A sore that doesnt heal
• Unusual bleeding or discharge
• Thickening or lump in breast or elsewhere
• Indigestion or difficulty in swallowing
• Obvious change in a wart or mole
• Nagging cough or hoarseness

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Treatments

• Early diagnosis
• Imaging
• Biopsy
• Chemotherapy
• Radiation
• Surgery

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How Can We Protect Ourselves from Cancer?

• Choose your parents carefully
• Dont get sunburned
• Dont smoke or use tobacco products
• Get regular check ups
• Protect yourself from STDs
• Watch your weight
• Eat high fiber foods and fresh fruits and
  vegetables

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II. The Production of Human Gametes Sperm and
Egg

1. Human body cells contain 46 chromosomes. They
   are diploid they contain two sets of chromosomes
   (2n).
2. In order to produce a zygote (fertilized egg)
   with 46 chromosomes, the sperm and egg must
   contain 23 chromosomes.
3. To reduce the number of chromosomes in the
   gametes (sperm and egg cells) the body must
   carry on a process called Meiosis (My-oh-sis) or
   reduction division

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D. Meiosis is similar to mitosis except

1. The parent cell divides twice
2. Four cells are produced instead of two.
3. The daughter cells are haploid (n). they contain
   only one set of chromosomes. ½ the number of
   chromosomes as the parent cell.
4. Gametes or sex cells (sperm and egg) are produced
   in meiosis, while somatic cells (body cells) are
   produced in mitosis.

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Crossing Over in Prophase I occurs only in Meiosis
Chiasma
Enzymes repair chromotids and sometimes new
chromotids form
Synapsis Homologous chromosomes pair and twist
during prophase I
Chiasma positions where the homologs cross and
break
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Crossing Over in Prophase I
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Meiosis Reduction Division
Prophase I Synapsis and crossing over
Interphase
Metaphase I
Telophase I and Cytokinesis
Anaphase I
No 2nd Interphase
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Prophase II
Metaphase II
Anaphase II
Telophase II
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SPERMATOGENESIS Production of Human Sperm
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46
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23
chromosomes
chromosomes
46
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Interphase
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Spermatogenesis
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OOGENESIS Production of Human Eggs
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46
Chromosomes
Chromosomes
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Egg
Uneven cytokenesis
chromosomes
chromosomes
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Polar Bodies
46
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Interphase
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Physical Evidence of Crossing Over Sordaria