In
genetics, a
deletion (also called
gene deletion,
deficiency, or
deletion mutation) (sign:
Δ) is a
mutation (a genetic aberration) in which a part of a
chromosome or a sequence of
DNA is lost during DNA replication. Any number of
nucleotides can be deleted, from a single base to an entire piece of chromosome. The smallest single base deletion mutations are believed occur by a single base flipping in the template DNA, followed by template DNA strand slippage, within the DNA polymerase active site. Deletions can be caused by errors in
chromosomal crossover during
meiosis, which causes several serious
genetic diseases. Deletions that do not occur in multiples of three bases can cause a
frameshift by changing the 3-nucleotide protein reading frame of the genetic sequence.