The presence of an uncomplimentary base in double-stranded DNA caused by spontaneous deamination of cytosine or adenine, mismatching during homologous recombination, or errors in DNA replication. Multiple, sequential base pair mismatches lead to formation of heteroduplex DNA; (NUCLEIC ACID HETERODUPLEXES).

Synonyms: Base Pair Mismatch, Base Pair Mismatches, Mismatch, Base Pair, Mismatches, Base Pair