Mutations that happen
during Transcription
and Translation
What happens if there is a mistake
(mutation) in the DNA code?
• Possibly proteins won’t be made or are made improperly.
• If the mutations occur in the gametes, the offspring’s DNA will
be affected positively, negatively, or neutrally.
• What can cause a mutation?
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Replication error
Transcription/translation error
Cell division error
Chemical agents (mutagens)
Spontaneous changes
Point mutation
• A point mutation is a change in a single base
pair in DNA.
• A change in a single nitrogenous base can
change the entire structure of a protein
because a change in a single amino acid can
affect the shape of the protein.
Point mutations
• May change the amino acid code if the
mutations occurs in the right place in the
code.
mRNA
Normal
Protein
Stop
Replace G with A
mRNA
Point
mutation Protein
Stop
Frameshift mutations
• Losing or gaining a single nucleotide base
• This mutation would cause nearly every amino
acid in the protein after the deletion to be
changed
Deletion of U
mRNA
Protein
Chromosomal mutations
• When a part of a chromosome is left out, a
deletion occurs
A B C D E
F G H
A B C E
F G H
Deletion
• When part of a chromatid breaks off and
attaches to its sister chromatid, an insertion
occurs.
A B C D E
F G H
A B C B C D E
Insertion
F G H
Changes to the chromosome
• When part of a chromosome breaks off and
reattaches backwards, an inversion occurs.
A B C D E F G H
A D C B E FGH
Inversion
• When part of one chromosome breaks off and
is added to a different chromosome, a
translocation occurs.
AB C D E F GH
WX Y Z
W X AB C DE F GH
Translocation
Y
Z
nondisjunction
failure either of two homologous chromosomes to
pass to separate cells during the first meiotic division
Repairing DNA
• Enzymes proofread the DNA and replace
incorrect nucleotides with correct nucleotides.
• The greater the exposure to a mutagen such
as UV light, the more likely is the chance that
a mistake will not be corrected.