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Mutations
Types of Mutations | Effects of Mutations
Mutations
Learning Objectives
• Identify different changes to DNA within both genes and
chromosomes
• Evaluate effects of changes to DNA on proteins produced
and organisms’ overall survival
Gene Mutations
• Gene mutation – a mutation that only affects one gene
– Insertion – an event in which one or more nucleotides are added
within a DNA sequence for a gene
– Deletion – an event in which one or more nucleotides are
removed from a DNA sequence for a gene
– Substitution (point mutation) – an event in which a nucleotide is
replaced with a different nucleotide
Type
Definition
Example
Insertion
A new nucleotide is added
Deletion
A nucleotide is removed
Substitution
(point mutation)
A nucleotide is replaced
with a different nucleotide
…TAGCCAGATA…
…TAGCGCAGATA…
…TAGCCAGATA…
…TAGCAGATA…
…TAGCCAGATA…
…TAGCCAGTTA…
Gene Mutations
• Types of mutations can be determined by
Step 1 Write the wild-type allele above the mutated allele so that
the bases line up.
Step 2 Starting on the right, look along both strands and underline
the first base that is different in the mutated allele.
Step 3 Based on the difference between the two strands, identify
the mutation that occurred.
Step 4 If possible, use the overall lengths of the two strands to
check your answer.
Gene Mutations Example
Ex) Which of the three gene mutations occurred to change the
sequence ACTAGATAGGCAT to ACTAGATAGCAGCAT?
Step 1
up.
Write the wild-type allele above the mutated allele so that the bases line
Wild-type ACTAGATAGGCAT
Mutated ACTAGATAGCAGCAT
Step 2 Starting on the right, look along both strands and underline the first base
ACTAGATAGGCAT
that is differentWild-type
in the mutated
allele.
Mutated ACTAGATAGCAGCAT
Step 3 Based on the difference between the two strands, identify the mutation
that occurred. An insertion occurred.
Step 4 If possible, use the overall lengths of the two strands to check your
Longer mutated strands reflect an insertion.
answer.
Yes.
Chromosomal Mutations
• Chromosomal mutation – a mutation that affects multiple
genes
– Chromosomal deletion – an event in which a piece of the
chromosome is deleted
• Can remove one or more genes
from chromosome
Chromosomal Mutations
• Chromosomal mutation – a mutation that affects multiple
genes
– Amplification – an event in which a large piece of the
chromosome is repeated
• Causes two or more copies of
one or more genes
Chromosomal Mutations
• Chromosomal mutation – a mutation that affects multiple
genes
– Inversion – an event in which one or more new nucleotides
removed and flipped before being reinserted
• Reverses orientation
Chromosomal Mutations
• Segments of DNA can also move from chromosome to
chromosome
– Chromosomal insertion – an event in which a piece of the
chromosome is removed and inserted into a different
chromosome
– Translocation – an event in which two pieces of different
chromosomes are interchanged
Chromosomal Mutations
• Some mutations happen during meiosis
– Homologous chromosomes are separated
• Each one goes into a different gamete
– Non-disjunction – an event in which the homologous
chromosomes do not separate and instead both go to the same
daughter cell
Effects of Mutations
• Mutations categorized by
– Change to nucleotides
– Effect on the polypeptide made
• Each type of change to nucleotide  certain type of
effect of polypeptide
Effects of Gene Mutations
• Substitution mutations can affect genes in multiple ways
– Different codon does not always change amino acid used
– Silent mutation – a mutation in which there is no effect on the
polypeptide chain created
• No outwardly visible affect
Effects of Gene Mutations
• Substitution mutations can affect genes in multiple ways
– Different codon does not always change amino acid used
– Missense mutation – a mutation that results in the insertion of a
different amino acid
• Amino acids now different
• Can change proteins created
Effects of Gene Mutations
• Substitution mutations can affect genes in multiple ways
– Different codon does not always change amino acid used
– Nonsense mutation – a mutation in which a stop codon is
expressed early, creating a shorter polypeptide chain
• Greatly affects protein created
Effects of Gene Mutations
• Genetic code has many redundancies, which can cause
silent mutations
Effects of Gene Mutations
• Insertions and deletions cause frameshift mutations
– Frameshift mutation – a mutation in which the codon reading
frame is altered, potentially changing all codons following
• Codons are read in groups of three nucleotides
• Addition or removal of a nucleotide changes the reading frame
• Different polypeptides produced
Effects of Chromosomal Mutations
• Chromosomal mutations affect multiple genes
– Have large impact on organism
– Non-disjunction
• Creates one gamete with extra copy and one with no information
• If either fuses with normal gamete, individual formed has abnormal
number of chromosomes
– Down syndrome – a human genetic
disorder caused by having an
extra chromosome #21
– Physical and mental retardation
Effects of Chromosomal Mutations
• Overexpression – the creation of more protein than
normal from a gene
– Creates more copies of protein than normal
– If chromosome is deleted or inversed, organism might not be
able to express any of the genes
Effects of Mutations
• Mutations categorized by effect on fitness
– Beneficial mutations – a mutation that increases an organism’s
fitness
• Fur color may allow organism to better blend into the environment,
avoiding predators
– Harmful mutation – a mutation that decreases an organism’s
fitness
• May make protein used to carry oxygen less efficient
– Neutral mutation – a mutation that does not affect an organism’s
fitness
• No change in proteins
• All silent mutations are neutral mutations
Mutations
Learning Objectives
• Identify different changes to DNA within both genes and
chromosomes
• Evaluate effects of changes to DNA on proteins produced
and organisms’ overall survival