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Deletion

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Deletion

en.wikipedia.org/wiki/Deletion_(genetics)

Deletions are unbalanced structural aberations (= they cause changes in the original amount of DNA) in which a part of the DNA is missing. They cause loss of genetic material.

Types of deletions:Edit

Terminal deletions: terminal deletions occur at the ends of a chromosome
Intercalary deletions: intercalary deletions occur within the chromosome - from the interior of the chromosome
microdeletions: cause loss of just a small amount of genetic material


Causes of deletions:Edit

Deletions can be caused by chromosomal breaks (generally leading to the loss of the acentric chromosome fragment), by unequal crossing-over (generation of deletions, but also duplications), as a consequence of abnormal segregation of chromosomes with balanced translocations or inversions. During pairing of chromosomes during meiosis the unpaired region generated by a deletion results in formation of a deletion/compensation loop.

08 15c-chromosome deletion-loop

http://bio3400.nicerweb.com/Locked/media/ch08/chromosome_deletion-loop.html







Genetic consequences of deletions:Edit

  • a heterozygote becomes monosomic for the part of genetic information, which is located on the corresponding fragment of normal chromosome
  • haploinsuficiency: inability of the single copy of genetic material to maintain the functions, for which two copies of DNA are necessary
  • LOH ("loss of heterozygosity"): loss of the dominant alele
  • gene deletion and contiguous gene syndrome (= syndrome caused by abnormalities of 2 or more genes, that are located next to each other on the chromosome)

Detection:Edit

Big deletions can be discovered by normal cytogenetic methods. Nowadays the most commonly used assay for deletion detection is the CGH (Comparative genome analysis).

Diseases/Syndromes:Edit

Interstitial deletions:

  • DiGeorge syndrome: microdeletion 22q11
  • Prader-Willi/ Angelman syndrome: 15q11-q13
  • Williams syndrome: 7q11

Terminal deletions:

  • Cri-du chat: del5p15

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