The answer to this is B, mutation.
mutation causes the genes or chromosomes to change permanently and these changes can be inherited to the future generations.
Those mistakes that cause mutations to occur may be either the faulty DNA replication or faulty separation of chromosomes during cell divisions.
Mutation may actually be beneficial, but it is rare. Some mutation does not bring any changes but many bring problems. One common result brought by mutation is Down's syndrome. This is because the 21st chromosomes failed to separate during meiosis.
So there you have it, the answer is B, mutation.
