Ms. DR’s Biology 621
Name: _____________________________________________________________Block: ____________ Date: ________________
Worksheet: Mutations Practice
There are three ways that DNA can be altered when a mutation (change in DNA
sequence) occurs.
1. Substitution – one base-pairs is replaced by another:
Example: G to C or A to G
C G T C
2. Insertion – one or more base pairs is added to a sequence:
Example: CGATGG –– CGAATGG
GCTACC GCTTACC
3. Deletion – one or more base pairs is lost from a sequence:
Example: CGATGG –– CATGG
GCTACC GTACC
There are five possible results of a mutation.
1. Silent mutation: When a base pair is substituted but the change still codes for
the same amino acid in the sequence:
Example: TCT and TCC both code for the amino acid Serine
2. Substitution: When a base pair is substituted and the new codon codes for a
different amino acid:
Example: TCT codes for Serine and CCT codes for Proline
3. Premature Stop: When a substitution results in the formation of a STOP codon
before all of the codons have been read and translated by the ribosome.
Example: GTGGTCCGAAACACC –– GTGGTCTGAAACACC
Val-Val-Pro-Asn-Thr Val-Val-STOP
4. Codon Deletion or Insertion: A whole new amino acid is added, or one is
missing from the mutant proton:
Example: GTGGTCCGAAACACC –– GTGGTCTGCCGAAACACC
Val-Val-Pro-Asn-Thr Val-Val-Cys-Pro-Asn-Thr
5. Frame Shift: When a deletion or insertion results in a different base pait being
the beginning of the next codon, changing the whole sequence of amino acids
Example: GTGGTCCGAAACACCT –– GTGGTCGAAACACCT
Val-Val-Pro-Asn-Thr Val-Val-Glu-Thr-Pro
