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12.4 Mutations
Think About It!
Complete the 2 tables on the first page of your handout. Try
this without using your notes first and only refer to your
notes on transcription and translation if you are struggling.
From your tables and both translated sequences, what do
you think a mutation is?
What is a mutation? And what can
a mutation do?
 A mutation is a
permanent change in
the DNA sequence of
a gene.
 Mutations in a gene's
DNA sequence can
alter the amino acid
sequence of the
protein encoded by the
gene.
Mutations happen REGULARLY
May occur in somatic cells (aren’t passed to
offspring)
• Skin cancer and leukemia
•
• May occur in gametes (eggs & sperm) and be
passed to offspring
• Certain types of cancer: the eye tumor
retinoblastoma and Wilms tumor, a childhood
malignancy of the kidney.
•
Most mutations have no effect on gene expression
• Many mutations are repaired by enzymes
• Some mutations may improve an organism’s
survival (beneficial) and/or produce genetic variety
Mutations to control genes can
transform one body part into
another. Scientists have studied
flies carrying Hox mutations
that sprout legs on their
foreheads instead of antennae!
Polydactyly – Common
disorder with extra fingers
and/or toes
How do mutations happen?
 The DNA sequence of each gene determines the amino acid
sequence for the protein it encodes. We can think about the DNA
sequence of a gene as a sentence made up entirely of threeletter words:
Thesunwashotbuttheoldmandidnotgethishat.
 The DNA sequence is interpreted in groups of three nucleotide
bases, called codons.
The sun was hot but the old man did not get
his hat.
 Each codon or 3-letter word in this case, specifies a single amino
acid in a protein.
The sun was hot but the old man did
not get his hat.
This sentence represents a gene.
Each letter corresponds to a
each word represents a
and
.
What would happen if you shifted the three-letter "reading
frame“? You would end up with:
T hes unw ash otb utt heo ldm and idn otg eth ish at.
Or
Th esu nwa sho tbu tth eol dma ndi dno tge thi sha t.
What other types of mutations can
occur in DNA sentences?
Point mutations are single nucleotide base
changes in a gene's DNA sequence. This type of
mutation can change the gene's protein product
in the following ways:
3 Types of Point Mutations
1. Missense mutations result in a
single amino acid change within
the protein.
2. Nonsense mutations create a
premature "translation stop
signal" (or "stop" codon),
causing the protein to be
shortened.
3. Silent mutations do not cause
amino acid changes within the
protein.
 Ex’s:
 Cystic Fibrosis
 Neurofibromatosis
 Sickle Cell Anemia
 Tay-Sachs
 Color Blindness
Missense Mutation
Nonsense Mutation
Insertion mutations & deletion
mutations
 Add or remove one or more
DNA bases.
 Insertion and deletion
mutations cause frameshift
mutations, which change the
grouping of nucleotide bases
into codons. This results in a
shift of "reading frame" during
protein translation.
Insertion Mutation
Deletion Mutation
But… mutations can also be beneficial
• Lactose Tolerance
• Antibiotic Resistance
• HIV Immunity
• Malarial Resistance from
Sickle Cell Anemia
Or they could be induced
• Mutagens
• Carcinogens
• Radiation
• UV light
• Environmental
• Heavy metals
• Chemical exposure
(VOC’s)
• Bacteria and Viruses
Skin Cancer
Skin cancer occurs when errors (mutations) form the
in the DNA of healthy skin cells. The mutations cause
the cells to grow out of control and form a mass of
cancer cells
The World Health Organization’s
International Agency for
Research on Cancer (IARC)
announced that it has moved UV
tanning beds to its highest
cancer risk category -"carcinogenic to humans."
The use of tanning beds
before age 30 is associated
with a 75% increase in
melanoma risk.
Lung Cancer
Smoking causes 87% of all lung cancer
cases. Smokers have approximately one
chance in 10 of developing lung cancer over
his/her lifetime.
Videos
Sickle Cell: http://www.dnalc.org/resources/3d/17-sickle-cell.html
Mutating virus: http://video.nationalgeographic.com/video/nationalgeographic-channel/shows/naked-science/ngc-deadly-mutation/
Radiation leading to mutations and cancer:
http://www.dnai.org/lesson/go/1738/1419
Addition and deletion mutations: http://highered.mcgrawhill.com/sites/0072556781/student_view0/chapter11/animation_quiz_4.html