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Defined: any change in an organism’s DNA
• Where: Single genes or entire chromosomes
– Some gene mutations change phenotype (physical characteristics)
• Example: Can cause a premature stop codon
– Some gene mutations don’t change phenotype.
• Example: Could be silent or occur in a non-coding region
• When: Throughout the life of the cell
Gene: Point Mutations
DNA
mRNA
Amino
acids
• Defined: one nucleotide is substituted for another
• Often repaired by spellchecker enzyme
• 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)
Point Mutation and Sickle Cell Disease
• Hemoglobin (protein) is
made from 574 amino
acids
• Sickle cell disease is
caused because of 1
wrong amino acid
Gene: Frame Shift Mutation
DNA
mRNA
Amino
acids
• Defined: insertion/deletion of a nucleotide
• Entire sequence of DNA/RNA after the mutation is
shifted (see animation)
• Much more serious to the structure/function of the final
protein
– mRNA sequence may have an early or late “stop codon”
Gene: Frame Shift Mutation
DNA
mRNA
Amino
acids
Impact on Offspring
If the mutated
sperm above were
to fertilize this
egg…
• Somatic cell mutations
– Affect only the
individual
– Not passed on to
future generations
– Ex: Muscle cell
mutation
• Germ cell mutations
– Germ cells = the
diploid cells that
undergo meiosis to
make sperm & egg
– May be passed to
future generations
Mutation Causes
• Mutagen: agents in the environment that can change
DNA
– Speed up replication process
– Break apart nucleotides
• Ex: UV from sunlight breaks hydrogen bond between
thymine (T) and adenine (A)
Review
1) How are proteins affected if the DNA code is
mutated?
Example: ATTCGAGG is mutated to ATTCGTGG
2) What is the difference between a point mutation and
frame shift mutations?
3) When are mutations passed on to future
generations?
4) What are germs cells?
5) What is a mutagen and how do they cause
problems?
6) Are all mutations considered bad/dangerous?
Explain.