BRAINCAKEMutation and Genetic Variation
A mutation is a change in the base sequence of DNA. Mutations are the only source of completely new alleles, so they are the original source of all genetic variation. Meiosis and fertilisation only shuffle alleles that already exist.
There are two broad kinds. Gene mutations change the base sequence within a single gene. Chromosome mutations change the structure or number of whole chromosomes, and can affect many genes at once.
Mutations happen spontaneously and at random, mostly as copying errors during DNA replication. The natural rate is low, but it is increased by mutagens. These include ionising radiation (X-rays, gamma rays), ultraviolet light, and some chemicals such as benzene and the tar in tobacco smoke.
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More in Genetic Information
- Meiosis and Genetic Variation
- Different Types of Mutation
- Random Fertilisation
- Genetics and Inheritance
- Alleles
- Polygenic Traits
- Monohybrid Crosses
- Test Cross
All 30 lessons in Genetic Information · All Edexcel A-level Biology topics