Biology / Unit 6: DNA and Protein Synthesis
6.5 Mutations
Notes
A mutation is a change in the DNA sequence.
- Point mutation (substitution): one base is swapped. It may change one amino acid, or none (silent), or create an early stop codon.
- Frameshift mutation: a base is inserted or deleted, shifting the reading frame and changing every codon after it. Usually very harmful.
- Chromosomal mutations change large pieces of chromosomes: deletion, duplication, inversion, translocation.
- Mutagens like UV light, X-rays and chemicals in tobacco smoke cause mutations.
- Mutations in body cells affect only that person; mutations in gametes can be passed to offspring. Some mutations are helpful and provide variation for evolution.
Practice
Sickle cell disease is caused by one base change that swaps one amino acid in hemoglobin. This is a:
Only one base is replaced.
Why is deleting one base usually more harmful than substituting one base?
Codons are read in threes, so losing one base scrambles everything downstream.
A mutation occurs in a skin cell of an adult. Can it be passed to the person's children?
Only mutations in sex cells (gametes) are inherited.
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