Gene Mutations
Target #17- I can describe a gene
mutation
• Gene mutation: a
permanent heritable
change in the sequence
of bases in DNA
– Effect can cause a range
of consequences from no
effect to complete
protein synthesis
inactivity
– Can occur on somatic
cells and on sex cells
• Three causes of gene mutation
Target #18- I can
explain the three
causes of gene
mutation
– Errors in replication
• Rare source of mutation
• DNA polymerase is responsible for
proof-reading the new strand against
the old strand
• Usually mismatched pairs are replaced
with the correct nucleotide
• Occurs 1 in every 1 billion nucleotides
– Mutagens
• Environmental influences
– Radiation, certain organic chemicals
• Rate of mutation is usually low because
DNA repair enzymes constantly
monitor and repair damages
– Transposons
• Specific DNA sequences that
have the ability to move to
different genes
– Can either increase or
decrease the expression of the
affected gene
• Nicknamed “jumping genes”
• Example
– Indian corn has both white and
red/black kernels
» Caused by a transposon
interrupting the expression
of the gene for black
kernel pigment
Target #19- I can
describe point
mutations
• Point Mutation
– Occurs in one or more
nucleotides
– Includes the substitution,
insertion or deletion of
nucleotides
• Can alter the type of amino acid
being produced, which may
result in the wrong protein being
synthesized
– Generally occurs during DNA
replication
Target #20- I can state what occurs
during a substitution mutation
• Substitutions
– One base is changed to a different base
– Usually affect no more than a single amino acid
• May have no effect at all
• Example
– If a mutation changed one codon of mRNA from CCC to
CCA, the codon would still code for the same amino acid
(Proline)
– If a change occurs in the first base of the codon CCC,
like to ACC, then the amino acid would be different.
Target #21- I
can state how
frameshift
mutations
affect protein
activity
• Insertions & Deletions
– Point mutations in which one
base is added or subtracted
from the DNA sequence
– Also known as frameshift
mutations
• Result in a shift of the reading
frame of the genetic message
• Can result in the changing of
the whole protein
– Results in a change in, or loss
of, the protein’s function
Target #22- I can summarize why genetic mutations may be
harmful
• A harmful change caused by genetic mutations may
result in the growth of cancer cells
– Development of cancer involves a series of accumulating
mutations that can be different for each type of cancer
• Several genes are involved with the suppression of tumor
formation, but when mutated cause cancer
– Proto-oncogenes and tumor-suppressor genes
• When those genes are mutated, they do not transcribe/translate
cell cycle regulating proteins correctly
– Results in the cell cycle not being controlled, and/or apoptosis is not
occurring
– Characteristics of Cancer Cells
• Genetically unstable
• Do not correctly regulate the cell cycle
• Escape the signals for cell death
Target #23- I can summarize why genetic mutations may be
beneficial
• Some genetic mutations have beneficial effects
– Results in the production of proteins with new or altered
functions that can be useful to organisms in different or
changing environments
• Example: mutations have helped many insects resist chemical pesticides
– Also results in organisms who are more successful at surviving
and producing offspring
• The source of all changes in organisms over time via evolution start with
genetic mutations