Introduction

The basic question that comes in our brain is where do we come from and how did we get where we are today? Geneticists and researcher have now discovered the human lineages of the world descended from 10 sons of a genetic Adam and 18 daughters of Eve. DNA studies point out that all modern humans share a common female ancestor who resided in Africa about 140,000 years ago, and all men share a common male ancestor who lived in Africa about 60,000 years ago. The mtDNA based studies suggest that all modern era humans descend from a group of African ancestors who near about 60,000 to 65,000 years ago initiated their astonishing journey (1). Cavalli-Sforza group by analysis of chromosome 21 markers and Y- chromosome also support the African dispersal theory (2), and in particular, other nuclear and mtDNA markers indicate eastern Africa as the origin of both African and Eurasian expansions (3).

Indian Social Groups

The story of ancestry of Indians is fascinating. The caste system in India is very old and its emergence is generally correlated with the appearance of the Aryans. Rigveda the Aryan religious book mentions of four varnas, viz Brahman, Rajanya, Vaisya and Sudra. This division was based on individual’s profession and duties, Brahmins, the priests or spiritual class, Rajanya (later mentioned as Kshatriya), the ruling class, Vaishya, the merchants and farmers; and Shudras, the servants. India, the mother of a billion people consists of 4693 communities with numerous of endogamous groups, 325 functioning languages among that fifteen are present on its paper bill and 25 scripts. We know it very well that India has served as a major corridor for the dispersal of human beings that started from Africa (4).

In India the first systematic survey of human variation was conducted by professor DN Majumdar of Lucknow University in united province present day Uttar Pradesh and later in Bengal (5).
Santachiara and his team from Italy by using RFLP of mtDNA showed that people of Punjab are more closer to caucasoid than south or Andhra Pradesh people (6).

Recently Bamshad’s group used five different set of data i.e. mtDNA HVR1 (hyper variable region 1) sequence, mtDNA RSPs, Y-chromosome STRs (Short-Tandem Repeats), Y-chromosome biallelic polymorphisms, and autosomal Alu polymorphisms to support that how Indian castes are related to European populations as one moves from lower to middle to upper caste populations. They showed that Y-chromosome STR data do not exhibit a closer affinity to Asians for each caste group. Upper castes are pretty close to Europeans than to Asians, middle castes are evenly far from the European and Asian while lower castes are closer to Asians. Y-chromosome biallelic polymorphism data suggest that upper castes are more close to European than lower caste (7). Bamshad’s group concluded that contemporary Hindu Indians are of proto-Asian origin with West Eurasian admixture. The main limitation of Bamshad’s study is that the study area was restricted to one geographical region namely Vizag in Andhra Pradesh.
More recently Reich and Lalji group have examined 560,132 autosomal SNPs in 132 Indian samples from 25 groups. These groups reside in fourteen states and one union territory (Andaman and Nicobar) of India from Kashmir to Kerala. Among 25 groups five belong to upper caste, six groups belong to lower castes, one group belongs to middle caste, ten groups belong to tribal and remaining two belong to hunter gatherer. Most of the groups fall to Indo-European or Dravidian language family. The research shows that most Indian populations are genetic admixtures of two ancient but genetically divergent groups, which each contributing around 39-71% of the DNA to most present day Indians (8). By principal component analysis (PCA) David and his team showed that siddi are an outlying group which is closely related with west Africans (YRI). Nyshi and Ao Naga who generally speak a tibeto-burman language are closely related to East Asians while Andamani did not show any closeness with Asian or Europeans. With the help of f3 and f4 ancestry estimation they developed a model which correlates the history of Indian and non Indian groups. In this model pathan, vaishya, meghawal and bhil are modeled as mixture of hypothetical Ancestral North Indian (ANI) and Ancestral South Indian (ASI). They also showed that ANI form a clade with Europeans (CEU) while Onge form a calde with ASI. Lalji singh group has already shown that Onge tribe doesn’t show any ancestry with population outside India within last 50,000 year but it shares some ancestry with Indian tribal population. They also suggested that founder effects are responsible for an even burden of recessive diseases in Indian population than consanguinity. That’s why recessive hereditary disease like The Madras pattern of Motor Neuron Disease (MMND), which is prevalent in the Chittor-Tirupati area and MYBPC3 mutation is only present in Indian population (9. In concise way we can say that modern day India is mixture of two group whom Reich et al term as “Ancestral North Indian” (ANI) population that is genetically close to Central Asians, Europeans, and Middle Easterners, and an “Ancestral South Indian” (ASI) population that is not close to any large contemporary group outside the Indian subcontinent.

Closing Remarks

The present day genetic diversity of India is maintained by caste system that follows endogamy (marriage within the group) which is common among Indians. Perhaps endogamy is one of the reason why recessive diseases are prevalent in Indian social group. Autosomal recessive disease means that the both the recessive gene is located on one of the autosomes. This means that males and females have equal probability to affect from this disease. Recessive hereditary diseases are seen among Indians who have descended from a small group of founder individuals. Promotion of inter caste marriages could helps us to abolish these diseases. The future study may also require more data set from a much wider array of populations, including a large sampling of tribal populations and Tibeto-Burman speakers to understand their specific contributions who are more closer to Han Chinese group (CHB) of China. We can also predict, there will be a lot of recessive diseases in India that will be different in each social group further future research also require to identify these diseases and its genetic mapping.

References

1. Doron M. Behar, Saharon Rosset, Jason Blue-Smith, Oleg Balanovsky, Shay Tzur, David Comas, R. John Mitchell, Lluis Quintana-Murci, Chris Tyler-Smith, R. Spencer Wells (2007) The Genographic Project public participation mitochondrial DNA database.PLoS Genet 3:e104

2. Jin L., Underhill P.A., Doctor V., Davis R.W., Shen P., Cavalli-Sforza L.L. and. Oefner P.J (1999) Distribution of haplotypes from a chromosome 21 region distinguishes multiple prehistoric human migrations, Proc. Natl. Acad. Sci. U.S.A. 96 pp. 3796–3800.

3. Watson E., Forster P., Richards M. and Bandelt H.-J., (1997) Mitochondrial footprints of human expansions in Africa, American Journal of Human Genetics 61 pp. 691–704

4. Cann RL (2001) Genetic clues to dispersal in human populations: retracing the past from the present. Science 291:1742–1748.

5. Majumdar, D. N. & Rao, C. R. (1960) Race Elements in Bengal: a Quantitative Study (Asia Publishing House).

6. Passarino G, Semino O, Bernini LF, Santachiara Benerecetti AS Pre-Caucasoid and (1996) Caucasoid genetic features of the Indian population, revealed by mtDNA polymorphisms. Am J Hum Genet 59:927–934

7. Bamshad M., Kivisild T., Watkins W.S., Dixon M.E., Ricker C.E., Rao B.B., Naidu J.M., Prasad B.V.R., Reddy P.G., Rasanayagam A., Papiha S.S., Villems R., Redd AJ, Hammer M.F., Nguyen S.V., Carroll M.L., Batzer M.A. and Jorde L.B., (2001) Genetic evidence on the origins of indian caste populations, Genome Res 11 pp. 994–1004.

8. Reich D., Thangaraj K., Patterson N., Price A. L. and Singh L. (2009)Reconstructing Indian population history Nature p489-494

9. Dhandapany, P. S., Sadayappan, S., Xue, Y., Powell, G. T., Rani, D. S., Nallari, P., Rai, T. S., Khullar, M., Soares, P., Bahl, A., Tharkan, J. M., Vaideeswar, P., Rathinavel, A., Narasimhan, C., Ayapati, D. R., Ayub, Q., Mehdi, S. Q., Oppenheimer, S., Richards, M. B., Price, A. L., Patterson, N., Reich, D., Singh, L., Tyler-Smith, C., and Thangaraj, K. (2009) A common Cardiac Myosin Binding Protein C variant associated with cardiomyopathies in South Asia. Nature Genet. 41, 187–191