Analysis Questions: Answer in complete sentences.
1. How many amino acids were affected in the point mutations?
2. How many amino acids were affected in the frameshift mutation?
3. Explain the difference between a frameshift mutation and a point mutation.
4. Which type of mutation, a frameshift or a point mutation, has more effect on the organism? Why?
5. Usually a frameshift mutation results in the synthesis of a nonfunctional protein. Why do you think
mutated proteins might not be functional?
6. Which type of point mutation would be insignificant to the organism? Why?
7. Which type of point mutation would have the greatest affect on the organism? Why?
8. Which type of point mutation would most likely cause major changes to physical structures of the
organism?
Name: _____________________________Date: _____________Period: ____
Types of Gene Mutations
Standard: 4c
Objective: Students will evaluate how mutations in the DNA sequence may or may not affect the expression of
the gene or the sequence of amino acids in the encoded protein.
2. silent point mutation: Happens when one base in a codon is changed but both code for the same
amino acid. Circle the mutated nitrogen base and amino acid.
original DNA:
Directions: There are two types of mutations, small-scale gene mutations and large-scale chromosomal
mutations. Example s of two basic types of gene mutations, frameshift (insertions and deletions), and point
(base substitution) are shown below.
TAC
CAT
TCT
C GG
T GT
AAA
A GG
G CG
ATT
mRNA:
amino acid:
A.
In frameshift mutations, an insertion or deletion of a base changes the reading frame of the
sequence since mRNA is read in groups of three nitrogen bases (codons). This causes several amino acids
to be affected unless the deletion or insertion is a group of three. There are very few examples of
frameshift mutation diseases in organisms because they are usually fatal to the organism because the
proteins do not function.
silent DNA:
substitute 9th
nucleotide TC
1. insertion frameshift:
mutated mRNA:
original DNA:
T HE
B OY
CUT
HI S
LI P
AND
ATE
H OT
DOG
mutate amino acid:
Insert a “S” after the
12th nucleotide.
amino acid:
3. nonsense point mutation: A base mutation that creates a new stop codon in place of an amino acid
causing a premature stopping of translation Circle the mutated nitrogen base and amino acid.
The insertion shifts the reading frame to the [ right / left ].
2.. deletion frameshift
original DNA
sequence:
original DNA:
T HE
B OY
CUT
HI S
LI P
AND
ATE
H OT
DOG
B.
The insertion shifts the reading frame to the [ right / left ].
CAA
ATA
GAA
CTT
nonsense DNA:
substitute 15th
nucleotide A T
mutated mRNA:
missense point mutation: Occurs when one nitrogen base is substituted for another nitrogen base
causing a different amino acid than previously to occur in the protein sequence. Circle the mutated
nitrogen base and amino acid.
original DNA:
AAT
amino acid:
In point mutations, a simple base substitution does not change the reading frame because one nitrogen
base is simply substituted with a different nitrogen base, so only one amino acid is affected unless there are
several base substitutions.
1.
G GT
mRNA:
Delete the 18th
nucleotide.
amino acid:
TAC
TAC
CAT
GCA
G AT
C TG
GCC
CAG
TTC
ATC
mutate amino acid:
C.
Complete the flow chart:
Types of gene mutations
mRNA:
amino acid:
missense DNA:
substitute 4th
nucleotide CG
mutated mRNA:
mutated amino acid:
Frameshift mutation
Point mutation
G AG
ACT