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

Mutations

Gene: Point Mutations

• 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)

DNA

mRNA

Amino acids

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

• 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”

DNA

mRNA

Amino acids

Gene: Frame Shift Mutation

DNA

mRNA

Amino acids

Impact on Offspring• 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

If the mutated sperm above were to fertilize this egg…

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)

Review1) 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.