Low copy repeats (LCRs), also known as segmental duplications (SDs), are highly
homologous
Homology may refer to:
Sciences
Biology
*Homology (biology), any characteristic of biological organisms that is derived from a common ancestor
*Sequence homology, biological homology between DNA, RNA, or protein sequences
* Homologous chrom ...
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 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 prima ...
. 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 (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 direct ...
(NHEJ) within this region are responsible for a wide range of disorders, including
Charcot–Marie–Tooth syndrome type 1A,
,
,
and
Potocki–Lupski syndrome.
Detection
The two widely accepted methods for SD detection
Genome-wide detection of segmental duplications
/ref> are:
*1. Whole-genome assembly comparison (WGAC), and
*2. Whole-genome shotgun sequence detection (WSSD).
See also
* Pseudogenes
* Molecular evolution
* Comparative genomics
* Inparanoid
* Tandem exon duplication
* 1q21.1 copy number variations
* Segmental duplication on the human Y chromosome
References
{{Repeated sequence
Molecular genetics
Mutation