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Mutations

A mutation is a permanent change in the
DNA sequence of a gene.
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Mutations in a gene's DNA sequence can
alter the amino acid sequence of the
protein encoded by the gene.
What is a mutation?
Like words in a sentence, the DNA
sequence of each gene determines the
amino acid sequence for the protein it
encodes.
 The DNA sequence is interpreted in
groups of three nucleotide bases, called
codons.
 Each codon specifies a single amino acid
in a protein.

How do mutations happen?

We can think about the DNA sequence of
a gene as a sentence made up entirely of
three-letter words. In the sequence, each
three-letter word is a codon, specifying a
single amino acid in a protein. Have a look
at this sentence:

Thesunwashotbuttheoldmandidnotget
hishat.
Mutate a sentence

Thesunwashotbuttheoldmandidnotget
hishat.

If you were to split this sentence into
individual three-letter words, you would
probably read it like this:

The sun was hot but the old man did
not get his hat.






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This sentence represents a gene.
Each letter corresponds to a nucleotide
base, and each word represents a codon.
What 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.
Now, going back to the original sentence:
 Thesunwashotbuttheoldmandidnotget
hishat.


See how you can mutate the reading
frame of this sentence by inserting or
deleting letters within the sentence.
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:
What types of mutations can occur
in DNA sentences?



Missense mutations are point mutations
that result in a single amino acid change
within the protein.
Nonsense mutations are point mutations
that create a premature "translation stop
signal" (or "stop" codon), causing the protein
to be shortened.
Silent mutations are point mutations that
do not cause amino acid changes within the
protein.


Insertion mutations and 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.
Gene mutation: Changes or shifts in one
or more nucleotides. (Point mutations or
frameshift mutations)
 Chromosomal mutation: Changes in the
number or structure of chromosomes.

Gene mutation vs. Chromosomal
mutation
Most mutations have no effect on gene
expression.
2. Some will cause changes in protein
production and will disrupt normal
biological activities.
3. Some mutations produce genetic variety
in a species and be highly beneficial.
1.
Significance of mutations