Point Mutations
Silent
Missense
Nonsense
Frameshift
Point Mutations
• A change in a single base pair within the DNA.
– Transition = a pyrimidine changing to another
pyrimidine (or purine to purine)
– Transversion = a purine changing to a pyrimidine (
or vise –versa)
Silent Mutation
• Does not alter the amino acid sequence of the
polypeptide even though the nucleotide
sequence has changed.
Missense Mutations
• Base substitutions in which an amino acid
change does occur.
– Example : sickle-cell anemia.
Nonsense Mutations
• Involves a change from a normal codon that
codes for a amino acid to a stop codon.
Frame-shift Mutations
• Involves the addition or deletion of a number
of nucleotides that is not divisible by 3. Causes
the sequence to shift to the right or left.
Table 16.1: Consequences of Point
Mutations Within the Coding
Sequence
• copy the example into your notes.