Defined: a change in an organism’s DNA
• Where: DNA or Chromosomes
• When: During replication, Synapses, or Crossing-Over
• Mutations can affect a single gene or an entire chromosome:
– 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
Gene: Point Mutations
DNA
mRNA
Amino
acids
Defined: one nucleotide is substituted for another
• Often repaired by DNA Polymerase (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)
Gene: Frame Shift Mutation (deletion)
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 early or late “stop codons”
Gene: Frame Shift Mutation (insertion)
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 early or late “stop codons”
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
• Natural selection often removes mutant alleles from a population
when they are less adaptive.
Mutation Causes
• Mutagen: agents in the environment that can change DNA
– Speed up replication process
– Break apart nucleotides
• Ex: UV sunlight breaks hydrogen bond between thymine (T)
and adenine (A)
REview
1) What is a mutagen and how do they cause problems?
2) How are proteins affected if the DNA code is mutated?
Example: ATTCGAGG is mutated to ATTCGTGG
3) What is the difference between a point mutation and
frame shift mutations?
4) When are mutations passed on to future generations?
5) Are all mutations considered bad/dangerous? Explain.