A mutation is any heritable change in the genome of an organism. For a population, heritable mutations provide the source of genetic variation, without which evolution could not occur: If all individuals of a species were genetically identical, every subsequent generation would be identical regardless of which members of the species reproduced successfully. For an individual organism, mutations are rarely beneficial, and many cause genetic diseases, including cancer. For researchers, mutations (either spontaneous or introduced) provide important clues about gene location and function.
Functional Consequences and Inheritance Patterns.
Mutations can be classified by their functional consequences. Mutations that inactivate the resulting protein, or prevent it from being made at all, are called loss-of-function mutations. These are usually recessive, since the organism still retains one functional copy on the other chromosome. Loss-of-function mutations may be dominant if the organism cannot compensate for the loss by using the other gene copy. Gain-of-function mutations are those in which the protein takes on a new function, or loses the ability to be regulated by other proteins. These mutations are typically dominant, since the new function may be deleterious even in the presence of a normal protein, encoded by the other gene copy.
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