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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.〔Banavali, Nilesh K. ("Partial base flipping is sufficient for strand slippage near DNA duplex termini." ) Journal of the American Chemical Society, 2013, 135(22), 8274-8282.〕〔Banavali, Nilesh K. ("Analyzing the Relationship between Single Base Flipping and Strand Slippage near DNA Duplex Termini." ) Journal of Physical Chemistry B, 2013, 117(46), 14320-14328.〕〔Manjari, Swati R., Pata, Janice D., Banavali, Nilesh K. ("Cytosine Unstacking and Strand Slippage at an Insertion–Deletion Mutation Sequence in an Overhang-Containing DNA Duplex." ) Biochemistry, 2014, 53(23), 3807-3816.〕 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. ==Causes== Causes include the following: * Losses from translocation * Chromosomal crossovers within a chromosomal inversion * Unequal crossing over * Breaking without rejoining 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Deletion (genetics)」の詳細全文を読む スポンサード リンク
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