Mutations Worksheet Name ________________ Per__________
Types of Mutations:
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).
Silent mutations
Most amino acids are encoded by several different codons. For example, if the third base in the
TCT codon for serine is changed to any one of the other three bases, serine will still be encoded.
Such mutations are said to be silent because they cause no change in their product and cannot be
detected without sequencing the gene (or its mRNA).
Nonsense mutations
With a nonsense mutation, the new nucleotide changes a codon that specified an amino acid to
one of the STOP codons (TAA, TAG, or TGA). Therefore, translation of the messenger RNA
transcribed from this mutant gene will stop prematurely. The earlier in the gene that this occurs,
the more truncated the protein product and the more likely that it will be
unable to 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 read and
translated. These changes are called frameshifts.
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There are three main types of mutations: point missense mutations, point nonsense mutations, and
frameshift mutations. In each of the following DNA sequences, you will use the mRNA and amino acid
sequences to identify the mutation that occurred and the effects of each on, if any. Look and analyze
carefully!
Original DNA Sequence:
T A C A C C T T G G C G A C G A C T
mRNA Sequence:
Amino Acid Sequence:
Mutated DNA Sequence #1:
T A C A T C T T G G C G A C G A C T
What’s the mRNA sequence? (Circle the change)
What will be the amino acid sequence?
Will there likely be effects?
What kind of mutation is this?
Mutated DNA Sequence #2:
T A C G A C C T T G G C G A C G A C T
What’s the mRNA sequence? (Circle the change)
What will be the amino acid sequence?
Will there likely be effects?
What kind of mutation is this?
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Mutated DNA Sequence #3:
T A C A C C T T A G C G A C G A C T
What’s the mRNA sequence? (Circle the change)
What will be the amino acid sequence?
Will there likely be effects?
What kind of mutation is this?
Mutated DNA Sequence #4:
T A C A C C T T G G C G A C T A C T
What’s the mRNA sequence? (Circle the change)
What will be the amino acid sequence?
Will there likely be effects?
What kind of mutation is this?
mRNA Codon Table
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