Final answer:
A mutation in a gene that does not improve or reduce fitness is called a neutral mutation. Neutral mutations do not affect an organism's fitness and do not provide any advantage or disadvantage. An example of a neutral mutation is a silent mutation.
Step-by-step explanation:
A mutation in a gene that does not improve or reduce fitness is called a neutral mutation. Neutral mutations are those that do not affect an organism's fitness.
They do not provide any advantage or disadvantage to the organism in terms of survival or reproduction. An example of a neutral mutation is a silent mutation, where a change in the DNA sequence of a gene does not result in a change in the amino acid sequence of the protein it codes for.