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

Mutations

Gene: Point Mutations

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)

DNA

mRNA

Amino acids

Gene: Frame Shift Mutation (deletion)

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”

DNA

mRNA

Amino acids

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– Affect only the individual– Not passed on to future

generations– Ex: Muscle cell mutation

• Germ cell mutations– May be passed to future

generations (either harmful or beneficial)

– Ex: Sperm 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)

REview1) 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.