3.22 - 3.23 - Mutation
Explain how mutations supply the genetic variants found within populations. Interpret evidence showing that most mutations have no observable effect, some have a small effect and only rarely does one have a large effect.
3.22, 3.23 — Mutation in populations
A mutation is a change in DNA. A genetic variant is a difference in a DNA sequence; a heritable variant can be passed to offspring. A phenotype is an observable characteristic.
A population is a group of organisms of the same species living in the same area at the same time. There is usually extensive genetic variation within a population: its members carry many different alleles and combinations of alleles.
New alleles ultimately arise through mutation. When a mutation is passed to offspring, that new variant can become part of the population's inherited genetic variation. Sexual reproduction can then place existing variants into many different combinations. Mutations do not appear because an organism needs a particular characteristic; a mutation is a change in DNA, not a purposeful response.
Finding a mutation does not tell you that the organism must look or function differently. The required pattern is:
| Frequency of outcome | Effect on phenotype |
|---|---|
| Most mutations | No effect on the phenotype |
| Some mutations | A small effect on the phenotype |
| Rarely, a single mutation | A significant effect on the phenotype |
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