Non-allelic homologous recombination (NAHR) is a form of

homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may ...

that occurs between two lengths of DNA that have high sequence similarity, but are not

allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...

s. It usually occurs between sequences of DNA that have been previously duplicated through evolution, and therefore have

low copy repeats 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% seq ...

(LCRs). These repeat elements typically range from 10–300 kb in length and share 95-97% sequence identity. During

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...

, LCRs can misalign and subsequent crossing-over can result in genetic rearrangement. When non-allelic homologous recombination occurs between different LCRs, deletions or further duplications of the DNA can occur. This can give rise to rare

genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorders ...

s, caused by the loss or increased copy number of genes within the deleted or duplicated region. It can also contribute to the

copy number variation Copy number variation (CNV) is a phenomenon in which sections of the genome are repeated and the number of repeats in the genome varies between individuals. Copy number variation is a type of structural variation: specifically, it is a type of d ...

seen in some gene clusters. As LCRs are often found in "hotspots" in the human genome, some

chromosomal A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

regions are particularly prone to NAHR. Recurrent rearrangements are nucleotide sequence variations found in multiple individuals, sharing a common size and location of break points. Therefore, multiple patients may manifest with similar deletions or duplications, resulting in the description of genetic

syndrome A syndrome is a set of medical signs and symptoms which are correlated with each other and often associated with a particular disease or disorder. The word derives from the Greek σύνδρομον, meaning "concurrence". When a syndrome is paired ...

s. Examples of these include NF1 microdeletion syndrome, 17q21.3 recurrent microdeletion syndrome or 3q29 microdeletion syndrome.

References

Genetics {{genetics-stub

See also

References