MUTATIONS

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					MUTATIONS
       What is a Mutation?
• A change in DNA
• Mutations are NOT
  Teenage Mutant Ninja
  Turtles or XMen!!!
• We are all mutants –
  products of the mutations
  in all of our ancestors before us
  How Do Mutations Occur?
• During DNA replication when bases are
  substituted, deleted, or added
• During mitosis and/or meiosis when
  chromosomes don’t divide properly
• During crossing over when chromatids
  “get lost” instead of being incorporated
  into its homolog’s DNA
• Aging causes mutations when segments
  of DNA are degraded (telomeres)
• Exposure to chemicals in the
  environment called mutagens (such as
  UV radiation, Xrays, some food dyes)
Somatic vs. Germ Cell Mutations
• Somatic mutations affect cells of the
  body, such as skin, muscle, etc.
• Somatic mutations can not be passed to
  offspring
• Germ cells are cells that divide to make
  gametes
• Germ cell mutations are passed to
  offspring
 Example of Germ Cell Mutation

• Queen Victoria had a germ cell mutation
  in cells that made her oocytes
• The mutation was in a gene that makes a
  protein for blood to clot
• She passed this mutation on to some of
  her children and they had hemophilia
• Gamete cells mutations can result in
  genetic disorders.
• If the parent survives with the disorder,
  it can be passed to another generation.
Example of Somatic Mutation
• UV radiation from the sun can mutate
  DNA in skin cells and cause cancer
• That cancer is not inherited
Gene vs. Chromosome Mutations

• Gene mutations affect one gene and
  therefore one protein (or polypeptide)
• Chromosome mutations affect a large
  part of a chromosome and all of the
  genes on that section of chromosome
          Gene Mutations
• Can occur during DNA replication
• They are often point mutations, which
  affect a small number of bases or
  sometimes just one base pair
    Types of Point Mutations
• Insertion (Addition)–one (or a few)
  bases is (are) inserted
• Deletion – one (or a few) base is (are)
  deleted
• Substitution – one base is substituted
  with another one
Deletion and Insertion Mutations
    Can Cause a Frameshift
Sickle Cell
• The mutation is in the gene for
  hemoglobin
• Malformed hemoglobin molecules cause
  red blood cells to “sickle”
• Red blood cells cause blood clots, which
  damage the kidneys and liver
• Severity varies from person to person
• Shortened life span (45 years is average)
• Pain due to blood clots
• Fatigue from lack of oxygen
Sickle Cell is Found in Certain
       Ancestral Groups
• Sickle cell evolved as a protection
  against malaria
• People with one sickle cell gene and one
  healthy gene don’t have sickle cell or get
  malaria!
              Tay-Sachs
• Children appear healthy at birth, but do
  not progress as other children
• Child will stop smiling, sitting up, etc.
• Blindness and eventually complete
  paralysis
• Usually results in death by age 5
• There is no cure
• Mutation in a gene for an enzyme that
  processes lipids in the brain (Hex A)
• The brain swells, crushing and killing
  parts of the brain
• Mutation occurred in central and
  eastern Europe
• Caused by a substitution mutation or a
  deletion mutation
              Cystic Fibrosis
• Deletion in a transport protein that allows Cl-
  to enter and exit cells
• Causes thick mucus to build up in lungs,
  which causes repeated lung infections
• Mucus clogs up pancreatic duct so food isn’t
  digested
• Mucus causes intestinal blockage
• Breathing treatments can loosen mucus
  in lungs to increase lung function and
  decrease chance of infection
• Treated with antibiotics for
  infections
• Use oral enzymes to digest food
   (increase in food intake to make
   up for undigested food)



The mutation is found here 
        on chromosome 7
• CF occurs in all ancestral backgrounds
  and is the most common fatal genetic
  disorder (about 1 in every 20 people
  carries the gene)
• Severity of disease varies from person to
  person and they die from a respiratory
  infection or lung failure
              Huntington’s
• Named after
   Dr. George Huntington
  who first described it
• Caused by an insertion
  mutation (CAG is
  repeated)

                             Nancy Wexler
• Causes jerky and uncontrolled
  movements
• Slurred speech
• Loss of memory
• Symptoms progress and get worse with
  time; caused by degeneration of nerve
  cells
• Symptoms usually appear between the
  ages of 35-40, but can be earlier
• Found in all major ethic groups
• Death is usually from pneumonia or
  choking
• Can live 10-20 years after the onset of
  the symptoms; some die earlier
                Albinism

• Mutation in one
of the genes for
producing melanin
which gives hair,
skin, and eyes
their color
• Albinos often
  have vision defects
   Nondisjunction Mutations
(Type of Chromosome Mutation)
• Occur when chromosomes fail
  to separate during meiosis
• Results in a cell with an extra
  chromosome or a chromosome
  missing
• The person wouldn’t have 46
  chromosomes, but 45 or 47
An Example of a Nondisjunction Mutation
                Down’s
• Named after Dr. Down that first
  described it
• Caused by 3 copies of the 21st
  chromosome (trisomy 21)
• Causes heart defects, mental
  retardation, unclear speech, rounded
  face, almond shaped eyes, poor muscle
  tone, fold in the eyelid
Notice the 3 21st chromosomes
   Another Example of Nondisjunction
             Klinefelter’s

• An extra X chromosome (XXY) in males
• Usually sterile, some have enlarged
  breasts, delayed learning, may be tall
  and thin, symptoms vary and may be
  undetectable
Notice the 3 sex chromosomes
How Klinefelter’s Occurs
And Another Example of Nondisjunction
              Turner’s
• Have 1 X chromosome (XO) - females
• About 98% of fetuses with Turner’s are
  spontaneously aborted (miscarried)
• Short, swelling of hands and feet, sterile,
  and other symptoms vary from person
  to person

				
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