Deletion (genetics)

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 left out during DNA replication. Any number of nucleotides can be deleted, from a single base to an entire piece of chromosome.^[1] Some chromosomes have fragile spots where breaks occur, which result in the deletion of a part of the chromosome. The breaks can be induced by heat, viruses, radiation, or chemical reactions. When a chromosome breaks, if a part of it is deleted or lost, the missing piece of chromosome is referred to as a deletion or a deficiency.^[2]

For synapsis to occur between a chromosome with a large intercalary deficiency and a normal complete homolog, the unpaired region of the normal homolog must loop out of the linear structure into a deletion or compensation loop.

The smallest single base deletion mutations occur by a single base flipping in the template DNA, followed by template DNA strand slippage, within the DNA polymerase active site.^[3][4][5]

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. Deletions are representative of eukaryotic organisms, including humans and not in prokaryotic organisms, such as bacteria.