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Concept
Délétion
Résumé
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. 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.
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.
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.
Causes include the following:
Losses from translocation
Chromosomal crossovers within a chromosomal inversion
Unequal crossing over
Breaking without rejoining
Types of deletion include the following:
Terminal deletion – a deletion that occurs towards the end of a chromosome.
Intercalary/interstitial deletion – a deletion that occurs from the interior of a chromosome.
Microdeletion – a relatively small amount of deletion (up to 5Mb that could include a dozen genes).
Micro-deletion is usually found in children with physical abnormalities. A large amount of deletion would result in immediate abortion (miscarriage).
Source officielle
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