DNA (Gene) Mutations
What is a gene mutation?
Parts of DNA will have a base (or
more) missing, added, or
incorrect
A mistake in the genetic code
Wrong instructions  wrong building
materials  wrong structure.
How common are mutations?
Mutations occurs at a
frequency of about 1 in every
1 billion base pairs
Everybody has about 6
mutations in each cell in their
body!
If I have that many mutations,
why don’t I look weird?
Mutations are not always seen.
Every part of your DNA doesn’t
make a protein or trait.
Remember introns and exons?
Some genes are recessive and
are therefore hidden, they can
be passed to your kids but you
don’t notice them.
The most common types of
gene mutations are:
Substitution
Point mutations
Frame shift mutations (2
kinds)
Insertion
Deletion
DNA (Gene) Mutation
Normal DNA:
CGA – TGC – ATC
Mutated DNA: CGA – TGC - TTC
What happened?
DNA (Gene) Mutation
#1
Normal DNA:
CGA – TGC – ATC
Mutated DNA: CGA – TGC - TTC
*Adenine was accidentally
replaced with thymine
*What is this mutation called?
Substitution (point
mutation)
Normal DNA: CGA – TGC – ATC
Amino acids: Ala -- Thr -- stop
Mutated DNA: CGA – TGC – TTC
Amino acids: Ala -- Thr -- Lys
What will happen to the
amino acids? How many
will be affected?
DNA (Gene) Mutation #2
Normal DNA:
CGA – TGC – ATC
Mutated DNA: CGA – TAG – CAT - C
What happened?
DNA (Gene) Mutations
Normal DNA:
CGA – TGC – ATC
Mutated DNA: CGA – TAG – CAT - C
*Adenine was inserted,causing the
remaining DNA to shift to the right
*What is this mutation called?
Insertion
Normal DNA:
Amino acids:
Mutated DNA:
Amino acids:
CGA – TGC – ATC
Ala -- Thr -- stop
CGA – TAG – CAT – C
Ala -- Tyr -- Val -- …..
What will happen to the
amino acids? How many
will be affected?
DNA (Gene) Mutation
#3
Normal DNA:
CGA – TGC – ATC
Mutated DNA: CGA – TCA- TC
What happened?
DNA (Gene) Mutation
Normal DNA:
CGA – TGC – ATC
Mutated DNA: CGA – TCA- TC
*Guanine was removed, causing the
remaining DNA to shift to the left
*What is this mutation called?
Deletion
Normal DNA:
CGA – TGC – ATC
Amino acids: Ala -- Thr -- Stop
Mutated DNA: CGA – TCA- TC
Amino acids: Ala -- Ser --…….
What will happen to the
amino acids? How many
will be affected?
• What causes mutations?
 Replication errors
 Transcription errors
 Cell division errors
 Spontaneous changes
 Mutagens
•Mutagen? What’s that?
•“Stuff” that causes mutations when a
cell is exposed.
•Examples: UV light, Xrays,
chemicals, etc.
What happens to someone with a
mutation?
That all depends…..
What kind of mutation it is.
How many proteins are affected.
Where in the polypeptide chain is the mutation.
How many cells does it affect.
Mutations can be fatal, harmful, beneficial
or nuetral.
• Which mutation would
have the least effect on an
organism?
•On intron sections of DNA
•On unexpressed recessive
traits.
•Point mutations/substitutions
•Only affects 1 amino acid.
• Which mutation would
have the most effect on an
organism?
•Frame-shift mutations:
•Deletions and insertions
affect all amino acids after the
mutation.
• When would a mutation
have the most effect on
an organism?
•During Meiosis
•If gametes are produced
with mutations, those
mutations will be passed
onto the offspring…….
•Every cell of organism
will contain mutation.
Repairing DNA
Enzymes proofread the DNA and
replace incorrect nucleotides with
correct nucleotides.
The greater the exposure to a mutagen
such as UV light, the greater the
chance that a mistake will not be
corrected.