MUTATIONS
What happens
when we
change DNA?
MUTATIONS
What do you think a
mutation is?
What happens to you
during a mutation?
MUTATIONS
Mutations are ANY
change in an
organism’s DNA.
Mutations usually
happen during if a
mistake is made
during replication
(S phase).
MUTATIONS
As we’ve discussed before, your cells have
many ways to prevent mutations from
happening.
Cells use proofreading when duplicating DNA.
If a cell detects a mistake is made in phase G2, it
self-destructs (apoptosis).
Your genetic code is degenerate. This means that
there are multiple possibilities to make most of
the amino acids.
MUTATIONS
Mutations will either change the individual
DNA sequences, or an entire chromosome.
We will look at DNA mutations first. There are
four types:
Substitution
Deletion
Insertion
Inversion
MUTATIONS
A substitution
switches one DNA
letter for another.
These are usually
point mutations –
mutations that only
affect one letter!
Example:
Original sequence:
THE FAT CAT ATE THE
RAT.
Mutant sequence:
THE FAT HAT ATE THE
RAT.
MUTATIONS
Many point mutations are also silent
mutations – they will NOT change the amino
acids that are created.
Original sequence: AUG CCA GGG UGU
Amino acids: Met – Pro – Gly - Cys
Mutant sequence: AUG CCC GGU UGU
Amino acids: Met – Pro – Gly - Cys
MUTATIONS
A deletion removes
one or more DNA
letters at once.
These are always
frameshift mutations
– mutations that
change how codons
are divided.
Example:
Original sequence:
THE FAT CAT ATE THE
RAT.
Mutant sequence:
THE FAT ATA TET HER
AT.
MUTATIONS
An insertion adds one
or more DNA letters
at once.
These are also always
frameshift mutations!
Example:
Original sequence:
THE FAT CAT ATE THE
RAT.
Mutant sequence:
THE FAT WCA TAT ETH
ERA T.
MUTATIONS
An inversion
reverses a sequence
of DNA letters.
These usually
happen during
mitosis (M phase),
as chromosomes
line up in
metaphase.
Example:
Original sequence:
THE FAT CAT ATE THE
RAT.
Mutant sequence:
THE FAT HTE TAT ACE
RAT.
MUTATIONS
Remember, point mutations leave the same
number of nucleotides.
In contrast, frameshift mutations either add
or remove nucleotides.
Point mutation:
AUG CGA UUA → AUG CUA UUA
Met – Arg – Leu → Met – Leu – Leu
Frameshift mutation:
AUG CGA UUA → AUG CGG AUU A
Met – Arg – Leu → Met – Arg - Iso
MUTATIONS
Now we will look
at chrmosomal
mutations.
Mutations that
affect ONLY ONE
chrmosome:
1. Deletion
2. Duplication
3. Inversion
MUTATIONS
Now we will look
at chrmosomal
mutations.
Mutations that
affect TWO
chrmosomes:
1. Insertion
2. Translocation
MUTATIONS: NON-DISJUNCTION
EX: TRISOMY 21 (DOWN SYNDROME)
 Sometimes, there is
an error when egg or
sperm cells divide,
resulting in too many
or too few
chromosomes.
 How do you think this
type of change would
impact an organism?