Transcript mutations - TeacherWeb

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 Clto 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