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MUTATIONS
Mutations
Defined: A change in an organism’s DNA.
• Many kinds of mutations can occur, especially during replication.
• 2 Types:
• 1) Gene Mutations:
– A point mutation, substitutes one nucleotide for another.
mutated
base
Gene: Point Mutations
DNA
mRNA
Amino
acids
• May lead to amino acid change
– See animation
• May not lead to any change (Silent Mutation)
– Ex: DNA “CCC” is mutated into “CCG”
» Same amino acid is created (glycine)
Gene Mutations Continued…
– A frameshift mutation (another type of gene mutation)
inserts or deletes a nucleotide in the DNA sequence.
• Entire sequence of DNA/RNA after the mutation is
shifted (see animations)
• Much more serious to the structure/function of the
final protein
– mRNA sequence may have early or late “stop
codons”
Gene: Frame Shift Mutation (deletion)
DNA
mRNA
Amino
acids
Gene: Frame Shift Mutation (insertion)
DNA
mRNA
Amino
acids
What type of mutation would this be?
• Original: The fat cat ate the wee rat.
• Mutation: The fat hat ate the wee rat.
What about this one?
• Original: The fat cat ate the wee rat.
• Mutation: The fat caa tet hew eer at.
Which has a much large effect on the end result?
Point or frameshift mutation?
Frameshift Mutation
2) Chromosomal Mutations
• Affect many genes.
• Chromosomal mutations may occur during crossing
over
– Gene duplication results from unequal crossing
over.
- Translocation results from the exchange of DNA
segments between nonhomologous chromosomes.
Mutations May or May Not Affect Phenotype
• Some gene mutations
• Some gene mutations do
change phenotype.
not affect phenotype.
– May cause a premature
– May be silent.
stop codon.
– May occur in a noncoding
– Can change protein
region.
structure.
– May not affect protein
– May cause gene
structure.
regulation.
blockage
no blockage
Ex: Cysitc Fibrosis (mutation causes excess mucus build up in airways)
Impact on Offspring
• Somatic cell mutations
• Germ cell mutations
– Affect only the individual
– May be passed to future
generations (either
– Not passed on to future
harmful or beneficial)
generations
– Ex: Sperm cell mutation
– Ex: Muscle cell mutation
– In nature, these are often
removed from a
population (natural
selection)- as these don’t
usually survive.
Causes of Mutations
• Replication errors can
cause mutations.
• Mutagens, such as UV
ray and chemicals, can
cause mutations.
• Some cancer drugs use
mutagenic properties
to kill cancer cells.