A mutant is a biological entity that has undergone a change in its genetic structure. In applied genetics, it is usual to speak of mutations as either harmful or beneficial. A harmful or deleterious mutation decreases the fitness of the organism. A beneficial or advantageous mutation increases the fitness of the organism. Changes in any structure can happen due to errors of multiple qualities. Some believe errors should be avoided at all costs, and errors are proof of failure. The future is unavoidable and will not care much about your petty ideas of right and wrong, of success or setback, of accomplishment or misfortune. In biology, a mutation is an alteration in the nucleotide sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mitosis, or meiosis or other types of damage to DNA, which then may cause an error during some forms of repair or an error during replication. Biological mutations may also result from the insertion or deletion of segments of DNA due to mobile genetic elements.