Mutations
Biology: Cambridge International A Level, topic 6.2.4
Mutations
Mutations are changes to the base sequence in the DNA. Mutations can be caused by addition, deletion and substitution of bases.
Mutations
- Mutations are changes to the DNA sequence.
- Mutations are almost always harmful because they interrupt the normal functioning of a protein.
- E.g. Cystic fibrosis is a genetic disorder caused by a mutation in the gene for a transmembrane protein.
Addition mutations
- Addition mutations are where one or more bases are added to the DNA sequence.
- E.g. ATCGTT → ATCCGTT
- In this example, a C is added in the middle of the DNA sequence.
Deletion mutations
- Deletion mutations are where one or more bases are removed from the DNA sequence.
- E.g. ATCGTT → ATCTT
- In this example, the G is deleted from the middle of the DNA sequence.
Substitution mutations
- Substitution mutations are where one or more bases are changed in the DNA sequence.
- E.g. ATCGTT → ACCGTT
- In this example, the first T is substituted for a C.
Causes of Mutation
Changes to the DNA sequence are known as gene mutations. Causes of mutation include:
DNA replication
- When DNA is replicated, the bases in the DNA sequence are read and copied.
- There can be errors in the replication process. These errors cause mutations.
- Mutations caused in DNA replication are spontaneous.
Mutagenic agents
- Mutagenic agents can also increase the rate at which mutations occur.
- Mutagenic agents include:
- Chemicals (e.g. bromine and benzene).
- Exposure to ionising radiation and ultraviolet radiation.
Chromosome mutations
- Chromosome mutations can also arise spontaneously during meiosis.
- Chromosome mutations can affect the number of chromosomes in a developing zygote. This is called aneuploidy.
- Meiosis is the production of haploid gametes. During meiosis, pairs of chromosomes are separated.
- Non-disjunction is when chromosome pairs do not separate properly.
Test yourself on Mutations
Which of the following statements about mutations are true?
Which of these is an addition mutation?
Which of these is NOT a cause of mutations?
Which of the following statements about mutations are true?