Which of the following correctly describes what a mutation is?
A. A change in the DNA code of an organism
B. A change to a gene of an organism
C. A change to the nucleotide sequence
D. All of the above

B. A change in the nucleotide sequence.

Mutation can be described as permanent change in the genetic material of living organisms (that is DNA, deoxyribonucleic acid).In other words, it depicts change in the sequence of nucleotide within gene (a segment of DNA that codes for particular protein). It can be caused due to error in the replication process or by the exposure to some chemical, physical or biological agents (that are known as mutagens, such as UV radiation).Mutation can result in altered protein, if change is within the coding region. There are primarily three types of mutation, which are substitution, insertion, and deletion mutation. This, option B) is the right answer.