Low copy repeats (LCRs), also known as segmental duplications (SDs), are highly homologous sequence elements within the eukaryotic genome.

Repeats

The repeats, or duplications, are typically 10–300 kb in length, and bear greater than 95% sequence identity. Though rare in most mammals, LCRs comprise a large portion of the

human genome The human genome is a complete set of nucleic acid sequences for humans, encoded as DNA within the 23 chromosome pairs in cell nuclei and in a small DNA molecule found within individual mitochondria. These are usually treated separately as the ...

owing to a significant expansion during

primate evolution The evolutionary history of the primates can be traced back 57-85/90 million years. One of the oldest known primate-like mammal species, ''Plesiadapis'', came from North America; another, '' Archicebus'', came from China. Other similar basal prim ...

. In humans, chromosomes Y and 22 have the greatest proportion of SDs: 50.4% and 11.9% respectively. Misalignment of LCRs during

non-allelic homologous recombination Non-allelic homologous recombination (NAHR) is a form of homologous recombination that occurs between two lengths of DNA that have high sequence similarity, but are not alleles. It usually occurs between sequences of DNA that have been previously ...

(NAHR) is an important mechanism underlying the chromosomal microdeletion disorders as well as their reciprocal duplication partners. Many LCRs are concentrated in "hotspots", such as the 17p11-12 region, 27% of which is composed of LCR sequence. NAHR and

non-homologous end joining Non-homologous end joining (NHEJ) is a pathway that repairs double-strand breaks in DNA. NHEJ is referred to as "non-homologous" because the break ends are directly ligated without the need for a homologous template, in contrast to homology direc ...

(NHEJ) within this region are responsible for a wide range of disorders, including Charcot–Marie–Tooth syndrome type 1A, hereditary neuropathy with liability to pressure palsies,

Smith–Magenis syndrome Smith–Magenis Syndrome (SMS), also known as 17p- syndrome, is a microdeletion syndrome characterized by an abnormality in the short (p) arm of chromosome 17. It has features including intellectual disability, facial abnormalities, difficulty s ...

, and Potocki–Lupski syndrome.

Detection

The two widely accepted methods for SD detectionGenome-wide detection of segmental duplications
/ref> are: *1. Whole-genome assembly comparison (WGAC), and *2. Whole-genome shotgun sequence detection (WSSD).

References

{{Repeated sequence Molecular genetics Mutation

Repeats

Detection

See also

References