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Types of Mutations
Knowing a few basic types of mutations can help you understand why some
mutations have major effects and some may have no effect at all.
Substitution
A substitution is
a mutation that
exchanges one base for
another (i.e., a change in a single “chemical letter” such as switching
an A to a G). Such a substitution could:
- change a codon to one that encodes a different amino acid and cause a
small change in the protein produced. For example, sickle
cell anemia is caused by a substitution in the beta-hemoglobin gene,
which alters a single amino
acid in the protein produced.
- change a codon to one that encodes the same amino acid and causes no
change in the protein produced. These are called silent mutations.
- change an amino-acid-coding codon to a single “stop” codon
and cause an incomplete protein. This can have serious effects since the
incomplete protein probably won’t function.
Insertion
Insertions are
mutations in which extra base pairs are inserted into a new place in
the DNA.
Deletion
Deletions are mutations
in which a section of DNA is lost, or deleted.
Frameshift
Since protein-coding DNA is divided into codons three bases long, insertions and deletions can alter a gene so
that its message is no longer correctly parsed. These changes are called frameshifts.
For example, consider the sentence, “The fat cat sat.” Each word represents
a codon. If we delete the first letter and parse the sentence in the same way, it doesn’t make sense.
In frameshifts, a similar error occurs at the DNA level, causing the codons to be parsed incorrectly.
This usually generates proteins that are as useless as “hef atc ats at” is uninformative.
There are other types of mutations as well, but this short list should give you an idea of the possibilities. |
Find out more about the details of mutation.
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