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author:("Singh, ladji")
26.  Deep Rooting In-Situ Expansion of mtDNA Haplogroup R8 in South Asia 
PLoS ONE  2009;4(8):e6545.
The phylogeny of the indigenous Indian-specific mitochondrial DNA (mtDNA) haplogroups have been determined and refined in previous reports. Similar to mtDNA superhaplogroups M and N, a profusion of reports are also available for superhaplogroup R. However, there is a dearth of information on South Asian subhaplogroups in particular, including R8. Therefore, we ought to access the genealogy and pre-historic expansion of haplogroup R8 which is considered one of the autochthonous lineages of South Asia.
Methodology/Principal Findings
Upon screening the mtDNA of 5,836 individuals belonging to 104 distinct ethnic populations of the Indian subcontinent, we found 54 individuals with the HVS-I motif that defines the R8 haplogroup. Complete mtDNA sequencing of these 54 individuals revealed two deep-rooted subclades: R8a and R8b. Furthermore, these subclades split into several fine subclades. An isofrequency contour map detected the highest frequency of R8 in the state of Orissa. Spearman's rank correlation analysis suggests significant correlation of R8 occurrence with geography.
The coalescent age of newly-characterized subclades of R8, R8a (15.4±7.2 Kya) and R8b (25.7±10.2 Kya) indicates that the initial maternal colonization of this haplogroup occurred during the middle and upper Paleolithic period, roughly around 40 to 45 Kya. These results signify that the southern part of Orissa currently inhabited by Munda speakers is likely the origin of these autochthonous maternal deep-rooted haplogroups. Our high-resolution study on the genesis of R8 haplogroup provides ample evidence of its deep-rooted ancestry among the Orissa (Austro-Asiatic) tribes.
PMCID: PMC2718812  PMID: 19662095
27.  A common MYBPC3 (cardiac myosin binding protein C) variant associated with cardiomyopathies in South Asia 
Nature genetics  2009;41(2):187-191.
Heart failure is a leading cause of mortality in South Asians. However, its genetic etiology remains largely unknown1. Cardiomyopathies due to sarcomeric mutations are a major monogenic cause for heart failure (MIM600958). Here, we describe a deletion of 25 bp in the gene encoding cardiac myosin binding protein C (MYBPC3) that is associated with heritable cardiomyopathies and an increased risk of heart failure in Indian populations (initial study OR = 5.3 (95% CI = 2.3–13), P = 2 × 10−6; replication study OR = 8.59 (3.19–25.05), P = 3 × 10−8; combined OR = 6.99 (3.68–13.57), P = 4 × 10−11) and that disrupts cardiomyocyte structure in vitro. Its prevalence was found to be high (~4%) in populations of Indian subcontinental ancestry. The finding of a common risk factor implicated in South Asian subjects with cardiomyopathy will help in identifying and counseling individuals predisposed to cardiac diseases in this region.
PMCID: PMC2697598  PMID: 19151713
28.  A Shared Y-chromosomal Heritage between Muslims and Hindus in India 
Human genetics  2006;120(4):543-551.
Arab forces conquered the Indus Delta region in 711 A.D. and, although a Muslim state was established there, their influence was barely felt in the rest of South Asia at that time. By the end of the tenth century, Central Asian Muslims moved into India from the northwest and expanded throughout the subcontinent. Muslim communities are now the largest minority religion in India, comprising more than 138 million people in a predominantly Hindu population of over one billion. It is unclear whether the Muslim expansion in India was a purely cultural phenomenon or had a genetic impact on the local population. To address this question from a male perspective, we typed eight microsatellite loci and 16 binary markers from the Y chromosome in 246 Muslims from Andhra Pradesh, and compared them to published data on 4,204 males from China, Central Asia, other parts of India, Sri Lanka, Pakistan, Iran, the Middle East, Turkey, Egypt and Morocco. We find that the Muslim populations in general are genetically closer to their non-Muslim geographical neighbors than to other Muslims in India, and that there is a highly significant correlation between genetics and geography (but not religion). Our findings indicate that, despite the documented practice of marriage between Muslim men and Hindu women, Islamization in India did not involve large-scale replacement of Hindu Y chromosomes. The Muslim expansion in India was predominantly a cultural change and was not accompanied by significant gene flow, as seen in other places, such as China and Central Asia.
PMCID: PMC2590854  PMID: 16951948
Y-chromosomal polymorphism; India; Muslim; Hindu
29.  Y-chromosomal insights into the genetic impact of the caste system in India 
Human genetics  2006;121(1):137-144.
The caste system has persisted in Indian Hindu society for around 3,500 years. Like the Y chromosome, caste is defined at birth, and males cannot change their caste. In order to investigate the genetic consequences of this system, we have analysed male-lineage variation in a sample of 227 Indian men of known caste, 141 from the Jaunpur district of Uttar Pradesh and 86 from the rest of India. We typed 131 Y-chromosomal binary markers and 16 microsatellites. We find striking evidence for male substructure: in particular, Brahmins and Kshatriyas (but not other castes) from Jaunpur each show low diversity and the predominance of a single distinct cluster of haplotypes. These findings confirm the genetic isolation and drift within the Jaunpur upper castes, which are likely to result from founder effects and social factors. In the other castes, there may be either larger effective population sizes, or less strict isolation, or both.
PMCID: PMC2590678  PMID: 17075717
Y chromosome; haplotype; human population substructure; Indian caste system
30.  Maternal Footprints of Southeast Asians in North India 
Human heredity  2008;66(1):1-9.
We have analyzed 7137 samples from 125 different caste, tribal and religious groups of India and 99 samples from three populations of Nepal for the length variation in the COII/tRNALys region of mtDNA. Samples showing length variation were subjected to detailed phylogenetic analysis based on HVS-I and informative coding region sequence variation. The overall frequencies of the 9-bp deletion and insertion variants in South Asia were 1.8% and 0.5%, respectively. We have also defined a novel deep-rooting haplogroup M43 and identified the rare haplogroup H14 in Indian populations carrying the 9bp-deletion by complete mtDNA sequencing. Moreover, we redefined haplogroup M6 and dissected it into two well-defined subclades. The presence of haplogroups F1 and B5a in Uttar Pradesh suggests minor maternal contribution from Southeast Asia to Northern India. The occurrence of haplogroup F1 in the Nepalese sample implies that Nepal might have served as a bridge for the flow of eastern lineages to India. The presence of R6 in the Nepalese, on the other hand, suggests that the gene flow between India and Nepal has been reciprocal.
PMCID: PMC2588665  PMID: 18223312
South Asia; 9bp indel; mtDNA; Haplogroup
31.  Phylogeography of mtDNA haplogroup R7 in the Indian peninsula 
Human genetic diversity observed in Indian subcontinent is second only to that of Africa. This implies an early settlement and demographic growth soon after the first 'Out-of-Africa' dispersal of anatomically modern humans in Late Pleistocene. In contrast to this perspective, linguistic diversity in India has been thought to derive from more recent population movements and episodes of contact. With the exception of Dravidian, which origin and relatedness to other language phyla is obscure, all the language families in India can be linked to language families spoken in different regions of Eurasia. Mitochondrial DNA and Y chromosome evidence has supported largely local evolution of the genetic lineages of the majority of Dravidian and Indo-European speaking populations, but there is no consensus yet on the question of whether the Munda (Austro-Asiatic) speaking populations originated in India or derive from a relatively recent migration from further East.
Here, we report the analysis of 35 novel complete mtDNA sequences from India which refine the structure of Indian-specific varieties of haplogroup R. Detailed analysis of haplogroup R7, coupled with a survey of ~12,000 mtDNAs from caste and tribal groups over the entire Indian subcontinent, reveals that one of its more recently derived branches (R7a1), is particularly frequent among Munda-speaking tribal groups. This branch is nested within diverse R7 lineages found among Dravidian and Indo-European speakers of India. We have inferred from this that a subset of Munda-speaking groups have acquired R7 relatively recently. Furthermore, we find that the distribution of R7a1 within the Munda-speakers is largely restricted to one of the sub-branches (Kherwari) of northern Munda languages. This evidence does not support the hypothesis that the Austro-Asiatic speakers are the primary source of the R7 variation. Statistical analyses suggest a significant correlation between genetic variation and geography, rather than between genes and languages.
Our high-resolution phylogeographic study, involving diverse linguistic groups in India, suggests that the high frequency of mtDNA haplogroup R7 among Munda speaking populations of India can be explained best by gene flow from linguistically different populations of Indian subcontinent. The conclusion is based on the observation that among Indo-Europeans, and particularly in Dravidians, the haplogroup is, despite its lower frequency, phylogenetically more divergent, while among the Munda speakers only one sub-clade of R7, i.e. R7a1, can be observed. It is noteworthy that though R7 is autochthonous to India, and arises from the root of hg R, its distribution and phylogeography in India is not uniform. This suggests the more ancient establishment of an autochthonous matrilineal genetic structure, and that isolation in the Pleistocene, lineage loss through drift, and endogamy of prehistoric and historic groups have greatly inhibited genetic homogenization and geographical uniformity.
PMCID: PMC2529308  PMID: 18680585
32.  Microsatellite-based phylogeny of Indian domestic goats 
BMC Genetics  2008;9:11.
The domestic goat is one of the important livestock species of India. In the present study we assess genetic diversity of Indian goats using 17 microsatellite markers. Breeds were sampled from their natural habitat, covering different agroclimatic zones.
The mean number of alleles per locus (NA) ranged from 8.1 in Barbari to 9.7 in Jakhrana goats. The mean expected heterozygosity (He) ranged from 0.739 in Barbari to 0.783 in Jakhrana goats. Deviations from Hardy-Weinberg Equilibrium (HWE) were statistically significant (P < 0.05) for 5 loci breed combinations. The DA measure of genetic distance between pairs of breeds indicated that the lowest distance was between Marwari and Sirohi (0.135). The highest distance was between Pashmina and Black Bengal. An analysis of molecular variance indicated that 6.59% of variance exists among the Indian goat breeds. Both a phylogenetic tree and Principal Component Analysis showed the distribution of breeds in two major clusters with respect to their geographic distribution.
Our study concludes that Indian goat populations can be classified into distinct genetic groups or breeds based on the microsatellites as well as mtDNA information.
PMCID: PMC2268706  PMID: 18226239
33.  Maternal Footprints of Southeast Asians in North India 
Human Heredity  2008;66(1):1-9.
We have analyzed 7,137 samples from 125 different caste, tribal and religious groups of India and 99 samples from three populations of Nepal for the length variation in the COII/tRNALys region of mtDNA. Samples showing length variation were subjected to detailed phylogenetic analysis based on HVS-I and informative coding region sequence variation. The overall frequencies of the 9-bp deletion and insertion variants in South Asia were 1.9 and 0.6%, respectively. We have also defined a novel deep-rooting haplogroup M43 and identified the rare haplogroup H14 in Indian populations carrying the 9-bp deletion by complete mtDNA sequencing. Moreover, we redefined haplogroup M6 and dissected it into two well-defined subclades. The presence of haplogroups F1 and B5a in Uttar Pradesh suggests minor maternal contribution from Southeast Asia to Northern India. The occurrence of haplogroup F1 in the Nepalese sample implies that Nepal might have served as a bridge for the flow of eastern lineages to India. The presence of R6 in the Nepalese, on the other hand, suggests that the gene flow between India and Nepal has been reciprocal.
PMCID: PMC2588665  PMID: 18223312
South Asia; 9bp indel; mtDNA; Haplogroup
34.  Austro-Asiatic Tribes of Northeast India Provide Hitherto Missing Genetic Link between South and Southeast Asia 
PLoS ONE  2007;2(11):e1141.
Northeast India, the only region which currently forms a land bridge between the Indian subcontinent and Southeast Asia, has been proposed as an important corridor for the initial peopling of East Asia. Given that the Austro-Asiatic linguistic family is considered to be the oldest and spoken by certain tribes in India, Northeast India and entire Southeast Asia, we expect that populations of this family from Northeast India should provide the signatures of genetic link between Indian and Southeast Asian populations. In order to test this hypothesis, we analyzed mtDNA and Y-Chromosome SNP and STR data of the eight groups of the Austro-Asiatic Khasi from Northeast India and the neighboring Garo and compared with that of other relevant Asian populations. The results suggest that the Austro-Asiatic Khasi tribes of Northeast India represent a genetic continuity between the populations of South and Southeast Asia, thereby advocating that northeast India could have been a major corridor for the movement of populations from India to East/Southeast Asia.
PMCID: PMC2065843  PMID: 17989774
35.  Y-chromosome evidence suggests a common paternal heritage of Austro-Asiatic populations 
The Austro-Asiatic linguistic family, which is considered to be the oldest of all the families in India, has a substantial presence in Southeast Asia. However, the possibility of any genetic link among the linguistic sub-families of the Indian Austro-Asiatics on the one hand and between the Indian and the Southeast Asian Austro-Asiatics on the other has not been explored till now. Therefore, to trace the origin and historic expansion of Austro-Asiatic groups of India, we analysed Y-chromosome SNP and STR data of the 1222 individuals from 25 Indian populations, covering all the three branches of Austro-Asiatic tribes, viz. Mundari, Khasi-Khmuic and Mon-Khmer, along with the previously published data on 214 relevant populations from Asia and Oceania.
Our results suggest a strong paternal genetic link, not only among the subgroups of Indian Austro-Asiatic populations but also with those of Southeast Asia. However, maternal link based on mtDNA is not evident. The results also indicate that the haplogroup O-M95 had originated in the Indian Austro-Asiatic populations ~65,000 yrs BP (95% C.I. 25,442 – 132,230) and their ancestors carried it further to Southeast Asia via the Northeast Indian corridor. Subsequently, in the process of expansion, the Mon-Khmer populations from Southeast Asia seem to have migrated and colonized Andaman and Nicobar Islands at a much later point of time.
Our findings are consistent with the linguistic evidence, which suggests that the linguistic ancestors of the Austro-Asiatic populations have originated in India and then migrated to Southeast Asia.
PMCID: PMC1851701  PMID: 17389048
36.  Lack of significant association of an insertion/deletion polymorphism in the angiotensin converting enzyme (ACE) gene with tropical calcific pancreatitis 
BMC Gastroenterology  2006;6:42.
The genetic basis of tropical calcific pancreatitis (TCP) is different and is explained by mutations in the pancreatic secretory trypsin inhibitor (SPINK1) gene. However, mutated SPINK1 does not account for the disease in all the patients, neither does it explain the phenotypic heterogeneity between TCP and fibro-calculous pancreatic diabetes (FCPD). Recent studies suggest a crucial role for pancreatic renin-angiotensin system during chronic hypoxia in acute pancreatitis and for angiotensin converting enzyme (ACE) inhibitors in reducing pancreatic fibrosis in experimental models. We investigated the association of ACE gene insertion/deletion (I/D) polymorphism in TCP patients using a case-control approach. Since SPINK1 mutations are proposed a modifier role, we also investigated its interaction with the ACE gene variant.
We analyzed the I/D polymorphism in the ACE gene (g.11417_11704del287) in 171 subjects comprising 91 TCP and 80 FCPD patients and compared the allelic and genotypic frequency in them with 99 healthy ethnically matched control subjects.
We found 46% and 21% of TCP patients, 56% and 19.6% of FCPD patients and 54.5% and 19.2% of the healthy controls carrying the I/D and D/D genotypes respectively (P>0.05). No significant difference in the clinical picture was observed between patients with and without the del allele at the ACE in/del polymorphism in both categories. No association was observed with the presence or absence of N34S SPINK1 mutation in these patients.
We conclude that the ACE insertion/deletion variant does not show any significant association with the pathogenesis, fibrosis and progression of tropical calcific pancreatitis and the fibro-calculous pancreatic diabetes.
PMCID: PMC1762011  PMID: 17163998
37.  Genotyping faecal samples of Bengal tiger Panthera tigris tigris for population estimation: A pilot study 
BMC Genetics  2006;7:48.
Bengal tiger Panthera tigris tigris the National Animal of India, is an endangered species. Estimating populations for such species is the main objective for designing conservation measures and for evaluating those that are already in place. Due to the tiger's cryptic and secretive behaviour, it is not possible to enumerate and monitor its populations through direct observations; instead indirect methods have always been used for studying tigers in the wild. DNA methods based on non-invasive sampling have not been attempted so far for tiger population studies in India. We describe here a pilot study using DNA extracted from faecal samples of tigers for the purpose of population estimation.
In this study, PCR primers were developed based on tiger-specific variations in the mitochondrial cytochrome b for reliably identifying tiger faecal samples from those of sympatric carnivores. Microsatellite markers were developed for the identification of individual tigers with a sibling Probability of Identity of 0.005 that can distinguish even closely related individuals with 99.9% certainty. The effectiveness of using field-collected tiger faecal samples for DNA analysis was evaluated by sampling, identification and subsequently genotyping samples from two protected areas in southern India.
Our results demonstrate the feasibility of using tiger faecal matter as a potential source of DNA for population estimation of tigers in protected areas in India in addition to the methods currently in use.
PMCID: PMC1636336  PMID: 17044939
38.  A novel mutation in STK11 gene is associated with Peutz-Jeghers Syndrome in Indian patients 
BMC Medical Genetics  2006;7:73.
Peutz-Jeghers syndrome (PJS) is a rare multi-organ cancer syndrome and understanding its genetic basis may help comprehend the molecular mechanism of familial cancer. A number of germ line mutations in the STK11 gene, encoding a serine threonine kinase have been reported in these patients. However, STK11 mutations do not explain all PJS cases. An earlier study reported absence of STK11 mutations in two Indian families and suggested another potential locus on 19q13.4 in one of them.
We sequenced the promoter and the coding region including the splice-site junctions of the STK11 gene in 16 affected members from ten well-characterized Indian PJS families with a positive family history.
We did not observe any of the reported mutations in the STK11 gene in the index patients from these families. We identified a novel pathogenic mutation (c.790_793 delTTTG) in the STK11 gene in one index patient (10%) and three members of his family. The mutation resulted in a frame-shift leading to premature termination of the STK11 protein at 286th codon, disruption of kinase domain and complete loss of C-terminal regulatory domain. Based on these results, we could offer predictive genetic testing, prenatal diagnosis and genetic counselling to other members of the family.
Ours is the first study reporting the presence of STK11 mutation in Indian PJS patients. It also suggests that reported mutations in the STK11 gene are not responsible for the disease and novel mutations also do not account for many Indian PJS patients. Large-scale genomic deletions in the STK11 gene or another locus may be associated with the PJS phenotype in India and are worth future investigation.
PMCID: PMC1609100  PMID: 17010210
39.  Genetic affinities among the lower castes and tribal groups of India: inference from Y chromosome and mitochondrial DNA 
BMC Genetics  2006;7:42.
India is a country with enormous social and cultural diversity due to its positioning on the crossroads of many historic and pre-historic human migrations. The hierarchical caste system in the Hindu society dominates the social structure of the Indian populations. The origin of the caste system in India is a matter of debate with many linguists and anthropologists suggesting that it began with the arrival of Indo-European speakers from Central Asia about 3500 years ago. Previous genetic studies based on Indian populations failed to achieve a consensus in this regard. We analysed the Y-chromosome and mitochondrial DNA of three tribal populations of southern India, compared the results with available data from the Indian subcontinent and tried to reconstruct the evolutionary history of Indian caste and tribal populations.
No significant difference was observed in the mitochondrial DNA between Indian tribal and caste populations, except for the presence of a higher frequency of west Eurasian-specific haplogroups in the higher castes, mostly in the north western part of India. On the other hand, the study of the Indian Y lineages revealed distinct distribution patterns among caste and tribal populations. The paternal lineages of Indian lower castes showed significantly closer affinity to the tribal populations than to the upper castes. The frequencies of deep-rooted Y haplogroups such as M89, M52, and M95 were higher in the lower castes and tribes, compared to the upper castes.
The present study suggests that the vast majority (>98%) of the Indian maternal gene pool, consisting of Indio-European and Dravidian speakers, is genetically more or less uniform. Invasions after the late Pleistocene settlement might have been mostly male-mediated. However, Y-SNP data provides compelling genetic evidence for a tribal origin of the lower caste populations in the subcontinent. Lower caste groups might have originated with the hierarchical divisions that arose within the tribal groups with the spread of Neolithic agriculturalists, much earlier than the arrival of Aryan speakers. The Indo-Europeans established themselves as upper castes among this already developed caste-like class structure within the tribes.
PMCID: PMC1569435  PMID: 16893451
41.  In situ origin of deep rooting lineages of mitochondrial Macrohaplogroup 'M' in India 
BMC Genomics  2006;7:151.
Macrohaplogroups 'M' and 'N' have evolved almost in parallel from a founder haplogroup L3. Macrohaplogroup N in India has already been defined in previous studies and recently the macrohaplogroup M among the Indian populations has been characterized. In this study, we attempted to reconstruct and re-evaluate the phylogeny of Macrohaplogroup M, which harbors more than 60% of the Indian mtDNA lineage, and to shed light on the origin of its deep rooting haplogroups.
Using 11 whole mtDNA and 2231 partial coding sequence of Indian M lineage selected from 8670 HVS1 sequences across India, we have reconstructed the tree including Andamanese-specific lineage M31 and calculated the time depth of all the nodes. We defined one novel haplogroup M41, and revised the classification of haplogroups M3, M18, and M31.
Our result indicates that the Indian mtDNA pool consists of several deep rooting lineages of macrohaplogroup 'M' suggesting in-situ origin of these haplogroups in South Asia, most likely in the India. These deep rooting lineages are not language specific and spread over all the language groups in India. Moreover, our reanalysis of the Andamanese-specific lineage M31 suggests population specific two clear-cut subclades (M31a1 and M31a2). Onge and Jarwa share M31a1 branch while M31a2 clade is present in only Great Andamanese individuals. Overall our study supported the one wave, rapid dispersal theory of modern humans along the Asian coast.
PMCID: PMC1534032  PMID: 16776823
42.  Global Patterns in Human Mitochondrial DNA and Y-Chromosome Variation Caused by Spatial Instability of the Local Cultural Processes 
PLoS Genetics  2006;2(4):e53.
Because of the widespread phenomenon of patrilocality, it is hypothesized that Y-chromosome variants tend to be more localized geographically than those of mitochondrial DNA (mtDNA). Empirical evidence confirmatory to this hypothesis was subsequently provided among certain patrilocal and matrilocal groups of Thailand, which conforms to the isolation by distance mode of gene diffusion. However, we expect intuitively that the patterns of genetic variability may not be consistent with the above hypothesis among populations with different social norms governing the institution of marriage, particularly among those that adhere to strict endogamy rules. We test the universality of this hypothesis by analyzing Y-chromosome and mtDNA data in three different sets of Indian populations that follow endogamy rules to varying degrees. Our analysis of the Indian patrilocal and the matrilocal groups is not confirmatory to the sex-specific variation observed among the tribes of Thailand. Our results indicate spatial instability of the impact of different cultural processes on the genetic variability, resulting in the lack of universality of the hypothesized pattern of greater Y-chromosome variation when compared to that of mtDNA among the patrilocal populations.
In most human societies, women traditionally move to their husband's home after marriage, and these societies are thus “patrilocal,” but in a few “matrilocal” societies, men move to their wife's home. These social customs are expected to influence the patterns of genetic variation. They should lead to a localization of male-specific Y-chromosomal variants and wide dispersal of female-specific mitochondrial DNA variants in patrilocal societies and vice versa in matrilocal societies. These predicted patterns have indeed been observed in previous studies of populations from Thailand. Indian societies, however, are endogamous, so marriage should always take place within a population, and these different patterns of genetic variation should not build up. The authors have now analyzed ten patrilocal and five matrilocal Indian populations, and find that there is indeed little difference between the patrilocal and matrilocal societies. The authors therefore conclude that patterns of genetic variation in humans are not universal, but depend on local cultural practices.
PMCID: PMC1435684  PMID: 16617372
43.  SSRD: Simple Sequence Repeats Database of the Human Genome 
Simple sequence repeats are predominantly found in most organisms. They play a major role in studies of genetic diversity, and are useful as diagnostic markers for many diseases. The simple sequence repeats database (SSRD) for the human genome was created for easy access to such repeats, for analysis, and to be used to understand their biological significance. The data includes the abundance and distribution of SSRs in the coding and non-coding regions of the genome, as well as their association with the UTRs of genes. The exact locations of repeats with respect to genomic regions (such as UTRs, exons, introns or intergenic regions) and their association with STS markers are also highlighted. The resource will facilitate repeat sequence analysis in the human genome and the understanding of the functional and evolutionary significance of simple sequence repeats. SSRD is available through two websites, and
PMCID: PMC2448451  PMID: 18629286
44.  Genome-wide analysis of microsatellite repeats in humans: their abundance and density in specific genomic regions 
Genome Biology  2003;4(2):R13.
Simple sequence repeats are found in most organisms, and occupy about 3% of the human genome. The densities of simple sequence repeats across the human chromosomes were found to be relatively uniform. Tri- and hexa-nucleotide repeats are more abundant in exons, whereas other repeats are more abundant in non-coding regions.
Simple sequence repeats (SSRs) are found in most organisms, and occupy about 3% of the human genome. Although it is becoming clear that such repeats are important in genomic organization and function and may be associated with disease conditions, their systematic analysis has not been reported. This is the first report examining the distribution and density of simple sequence repeats (1-6 base-pairs (bp)) in the entire human genome.
The densities of SSRs across the human chromosomes were found to be relatively uniform. However, the overall density of SSR was found to be high in chromosome 19. Triplets and hexamers were more predominant in exonic regions compared to intronic and intergenic regions, except for chromosome Y. Comparison of densities of various SSRs revealed that whereas trimers and pentamers showed a similar pattern (500-1,000 bp/Mb) across the chromosomes, di- tetra- and hexa-nucleotide repeats showed patterns of higher (2,000-3,000 bp/Mb) density. Repeats of the same nucleotide were found to be higher than other repeat types. Repeats of A, AT, AC, AAT, AAC, AAG, AGC, AAAC, AAAT, AAAG, AAGG, AGAT predominate, whereas repeats of C, CG, ACT, ACG, AACC, AACG, AACT, AAGC, AAGT, ACCC, ACCG, ACCT, CCCG and CCGG are rare.
The overall SSR density was comparable in all chromosomes. The density of different repeats, however, showed significant variation. Tri- and hexa-nucleotide repeats are more abundant in exons, whereas other repeats are more abundant in non-coding regions.
PMCID: PMC151303  PMID: 12620123

Results 26-44 (44)