INTRODUCTION:
Tracing about the origin and ancestral links of homo sapiens have
been the subject of curiosity for various scientists. And a number of
scholars have devoted themselves to disclose these hidden mysteries
of Human origin and dispersal on earth.
Where did we come from, and how did we get here? This is the
question which genetic anthropology field is seeking an answer for.
DNA studies indicate that all modern humans share a common
female ancestor who lived in Africa about 140,000 years ago, and all
men share a common male ancestor who lived in Africa about 60,000
years ago. These were not the only humans who lived in these eras,
and the human genome still contains many genetic traits of their
contemporaries. Humanity’s most recent common ancestors are
identifiable because their lineages have survived by chance in the
special pieces of DNA that are passed down the gender lines nearly
unaltered from one generation to the next. These ancestors are part of
a growing body of fossil and DNA evidence indicating that modern
humans arose in sub-Saharan Africa and began migrating, starting
about 65,000 years ago, to populate first southern Asia, China, Java,
and later Europe. Each of us living today has DNA that contains the
story of our ancient ancestors’ journeys.
When DNA is passed to our next generation, the processes that make
each person unique from their parents is the combination of both their
genomes. Some special pieces of DNA, however, remain virtually
unaltered as they pass from parent to offsprings. One of these pieces
are carried by Y chromosome. It is passed only from father to son.
Secondly, mitochondrial DNA (mtDNA), is passed (with few
exceptions) only from mother to child. Since the DNA in the Y
chromosome does not undergo crossing over, it is like a genetic
surname that allows scientists to trace back their paternal lineages.
Similarly, mtDNA allows both men and women to trace their
maternal lineages. Both the Y chromosome DNA and mtDNA are
subject to occasional harmless mutations that become inheritable
genetic markers. After several generations, almost all male and female
inhabitants of the region in which it arose carry a particular genetic
marker. When people leave that region, they carry the marker with
them. By studying the genes of many different indigenous
populations, scientists can trace when and where a particular marker
arose. Each marker contained in a person’s DNA represents a location
and migration pattern of that person’s ancient ancestors. For example,
roughly 70% of English men, 95% of Spanish men, and 95% of Irish
men have a distinctive Y-chromosome mutation known as M173. The
distribution of people with this mutation, in conjunction with other
DNA analysis, indicates that they moved north out of Spain into
England and Ireland at the end of the last ice age
(genomics.energy.gov).
Information about the history of our species comes from two main
sources: the paleo-anthropological record and historical inferences
based on current genetic differences observed in humans. Although
both sources of information are fragmentary, they have been
converging in recent years on the same general story (Underhill et;
al.).
Since the 1990s, it has become common to use multilocus genotypes
to distinguish different human groups and to allocate individuals to
groups (Bamshad et al. 2004). These data have led to an examination
of the biological validity of races as evolutionary lineages and the
description of races in cladistic terms. The technique of multilocus
genotyping has been used to determine patterns of human
demographic history. Thus, the concept of “race” afforded by these
techniques is synonymous with ancestry broadly understood (Berg et
al.,).
Y chromosome and mitochondrial DNA are transmitted uni-parentally
through father and mother, respectively and don’t under go any
recombination. Hence, markers present on both are useful to trace the
paternal and maternal lineages. Haplotypes can be constructed by
combining the allelic status of multiple markers, which would provide
adequate information for establishing paternal lineages. The non-
coding region (D-loop) of mtDNA, which harbors two hyper variable
regions (HVR I and HVRII), shows variation between different
populations. A large number of studies have been conducted on
various populations using Y chromosome markers and mtDNA D-
loop region to understand their origin, evolution and migration.
Indian populations reveal striking diversities in terms of language,
marriage practices as well as in their genetic architecture. The social
structure of the Indian population is governed by the hierarchical caste
system. In India, there are nearly 5,000 well-defined endogamous
populations. In addition to the native populations, there are a few
migrant populations inhabiting various parts of India. Several
important historical migrations into India caused amalgamation of
migrant populations with the local population groups. Major
demographic event like migrations, population bottlenecks and
population expansion leave genetic imprints and alter gene
frequencies. These imprints are passed onto successive generations,
thus preserving the population’s history within the population.
Therefore, we have undertaken to disclose the genetic information
about how different caste and tribal populations of India help to
construct ecognize and help to construct the evolutionary tree
(Cavalli-Sforza et al.,).
Two major routes have been proposed for the initial peopling of East
Asia; one via Central Asia to Northeast Asia, which subsequently
expanded towards Southeast Asia and beyond, and the other through
India to Southeast Asia and further to different regions of East
Asia.[1] It is pertinent in this context that the Indian subcontinent has
been considered as a major corridor for the migration of human
populations to East Asia.[2-4] Given its unique geographic position,
Northeast India is the only region which currently forms a land
bridge between the Indian subcontinent and Southeast Asia, hence
hypothesized as an important passage for the initial peopling of East
Asia. This region is inhabited by populations belonging to Indo-
European, Tibeto-Burman and Austro-Asiatic linguistic families.
‘‘BHUMIJ TRIBE’’ come under austro-asiatic linguistic
population. Austro-Asiatic speakers, hypothesized as probably the
earliest settlers in the Indian subcontinent ([5] and references their
in), are also found in other parts of India as well as in East/Southeast
Asia. Therefore, if Northeast India had served as an initial corridor, it
is likely that the Austro-Asiatic tribes of this region should provide
hitherto missing genetic link, which may reflect genetic continuity
between Indian and East/Southeast Asian populations. Based on
mitochondrial DNA (mtDNA) and Y-chromosome markers, Cordaux
et al. [6] observed genetic discontinuity between the Indian and
southeast Asian populations and inferred that Northeast India might
have acted as a barrier rather than the facilitator of the movement of
populations both into and out of India.
However, this study include only ‘‘BHUMIJ’’ Tribe of Jharkhand
region from Jamshedpur district. Further evidence is needed by way
of determining the mtDNA and Y-chromosome haplogroups/lineages
of the Austro-Asiatic tribes of the northeastern region and their
comparison with appropriate set of South and Southeast Asian
populations. Jharkhand is basically an agricultural land.
Geographically it is covered by jungles, mountains, rivers and
Chotanagpur plateau etc.
1.2 BACKGROUND :
HUMAN GENOME DIVERSITY PROJECT (HGDP) :
The HGD Project was started internationally on mid-September
of 1993 and it has 13 countries participating in it. The Human
Genome Diversity Project is an international project that seeks to
understand the diversity and unity of the entire human species.
The Human Genome Diversity Project (HGDP) aims to collect
biological samples from different population groups throughout the
world, with the aim of building up a representative database of human
genetic diversity. This seems a laudable aim, but the Project has been
enmeshed in massive controversy since it was first proposed in 1991,
with violent reactions from many of the indigenous people’s groups it
proposes to study.
The eminent geneticist Luigi Luca Cavalli-Sforza of Stanford
University first conceived by the HGDP. For many years, he and other geneticists and anthropologists have been visiting different ethnic
groups around the world, collecting samples, and trying to build up a
picture of how different human populations are related to each other.
The samples are seen as immensely valuable, but they are in
laboratories spread around the world. In 1991, Cavalli-Sforza and a
number of colleagues wrote a letter to the scientific journal, Genomics,
pointing out the need for a systematic study of the whole range of
human genetic diversity, within the context of the Human Genome
Project. They pointed to a problem: ‘The populations that can tell us
most about our evolutionary past are those that have been isolated for
some time, are likely to be linguistically and culturally distinct and are
often surrounded by geographic barriers. Such isolated populations are
being rapidly merged with their neighbours, however, destroying
irrevocably the information needed to reconstruct our evolutionary
history. It would be tragically ironic if, during the same decade that
biological tools for understanding our species were created, major
opportunities for applying them were squandered.
Major demographic events like migration, population
bottlenecks and population expansion leave genetic imprints where
gene frequency of the genome is altered (Thangaraj et, al., 1998).
These imprints are passed onto successive generations thus preserving
the population history within the population. In general, human
beings group themselves into units in such a way that members
between units rarely exchange genes due to cultural and
geographical barriers resulting in genetic divergence of population.
The Human Genome Diversity Project proposed in early nineties is a
combined effort preceded by anthropologists, geneticists, doctors,
linguists and other scholars from around the world aims at collecting
the blood samples from different ethnic populations throughout the
world aiming at building up a representative database of human genetic
diversity.
The reason lying behind selecting only tribes for sampling is that they
are believed to have been isolated during an evolutionary time,
linguistically and culturally distinct and are often isolated by
geographic barriers and thus prove to be best tools for study.
IN THIS PROJECT, THE SUBJECT OF GENETIC STUDY IS
‘‘BHUMIJ TRIBE’’ FROM JHARKHAND (CHOTANAGPUR
PLATEAU), INDIA .
1.3 STATEMENT OF PURPOSE :
How does DNA helps us to trace back?
Y chromosome and mitochondrial DNA are transmitted uni-parentally through father and mother respectively and do not undergo any
recombination. Hence, markers present on both are useful to trace the
paternal and maternal lineages. Haplotypes can be constructed by
combining the allelic status of multiple markers, which would provide
adequate information for establishing paternal lineages. The non-coding
region (D-loop) of mtDNA, which harbors two hyper variable regions
(HVR I and HVRII), shows variation between different populations. A
large number of studies have been conducted on various populations
using Y chromosome markers and mtDNA D-loop region to understand
their origin, evolution and migration.
Indian populations reveal striking diversities in terms of
language, marriage practices as well as in their genetic architecture. The
social structure of the Indian population is governed by the hierarchical
caste system. In India, there are nearly 5,000 well-defined endogamous
populations. In addition to the native populations, there are a few
migrant populations inhabiting various parts of India Several important
historical migrations into India caused amalgamation of migrant
populations with the local population groups. Major demographic event
like migrations, population bottlenecks and population expansion leave
genetic imprints and alter gene frequencies. These imprints are passed
onto successive generations, thus preserving the population’s history
within the population. Therefore, we have undertaken to disclose the
genetic information about caste and tribal populations of India to
construct ecognize and to use the ecognize data to construct the
phylogenetic tree.
In future the recorded data of mutated sites of a particular
haplogroup can help the scientists to trace the cause and solution to
many new diseases and help them to develop ne techniques of
diagnosis and design new drugs.
1.4 AIMS AND OBJECTIVES OF THE STUDY :
GOALS OF HGD PROJECT:
The Human Genome Diversity Project is a collaborative research project
that is being developed on a global basis under the auspices of the
Human Genome Organization (HUGO).
¾ The overall goal of the project is to arrive at a much more precise
definition of the origins of different world populations by integrating
genetic knowledge, derived by applying the new techniques for studying
genes, with knowledge of history, anthropology and language.
¾ To investigate the variation occurring in the human genome by
studying samples collected from populations that are representative of all
of the world’s peoples.
¾ To create a resource for the benefit of all humanity and for the
scientific community worldwide.
The resource will exist as a collection of biological samples that
represents the genetic variation in human populations worldwide and
also as an open, long-term, genetic and statistical database on variation
in the human species that will accumulate as the biological samples are
studied by scientists from around the world.
The major goals of HGDP:
¾ To identify all the approx 20,000-25,000 genes in human DNA,
determination of the sequence of the 3 billion chemical base pair that
make up human DNA.
¾ In silico storage of all DNA database. Improve tools for data analysis.
¾ Transfer related technologies to the private sector. Address the
ethical, legal and social issues (ELSI) that may arise from the project.
¾ To provide information regarding human biological relationship
among different groups and human history.
¾ To understand the cause and diagnostics of human diseases.
BENEFITS AND IMPLIFICATIONS OF HGDP:
The project will reap fantastic benefits for human kind, some that we can
anticipate and other that will surprise us. Generations of biologists and
researchers have been provided with detailed DNA information that will
be the key to understanding the structure, organization and function of
DNA in chromosome. The information from HGDP provides
information to clarify the origin and biological relationship of specific
human populations and the evolution of human being in particular. The
variations of frequencies in various populations can reveal how recently
they shared a large pool of common ancestors.
HGDP IN INDIA:
In India, Centre for Cellular and Molecular Biology [ CCMB], Hyderabad has pioneered the Human Genome Diversity Project in
collaboration with several other institutes and universities. Around
6,200 different unrelated individuals have been sampled from various
Indian populations & have been analyzed for their genetic diversity and
phylogeny.
The origins of Indian tribes, who presently constitute about 8% of total
population of India, have been subject to numerous genetic studies. India
is a land of enormous human genetic, bio-geographic, socio-economic,
cultural and linguistic diversity. More than 300 tribal groups are
recognized in India and they are densest in the central and southern
province. There are more than 800 dialects and a dozen major languages,
grouped into those of Dravidian South India and Indo-Aryan North
India. The resulting hypotheses range from referring to some tribes as
the descendents of the original Paleolithic inhabitants of India while
some are the recent immigrants. Hence, genetic diversity in India
provides important clues to the evolutionary history of human beings.
TRACING GENETIC DIVERSITY:
The past decade of advances in molecular genetic technology has
heralded a new era for all evolutionary studies, but especially the science
of human evolution. Data on various kinds of DNA variation in human
populations have rapidly accumulated. There is increasing recognition of
the importance of this variation for medicine and developmental biology
and for understanding the history of our species. Haploid markers from
mitochondrial DNA and the Y chromosome have proven invaluable for
generating a standard model for evolution of modern humans.
Conclusions from earlier research on protein polymorphisms have been
generally supported by more sophisticated DNA analysis. Co-evolution
of genes with language and some slowly evolving cultural traits, together
with the genetic evolution of commensals and parasites that have
accompanied modern humans in their expansion from Africa to the other
continents, supports and supplements the standard model of genetic
evolution. The advances in our understanding of the evolutionary history
of humans attest to the advantages of multidisciplinary research.
Although molecular genetic evidence continues to accumulate that is
consistent with a recent common African ancestry of modern humans, its
ability to illuminate regional histories remains incomplete. A set of
unique event polymorphisms associated with the non-recombining
portion of the Y-chromosome (NRY) addresses this issue by providing
evidence concerning successful migrations originating from Africa,
which can be interpreted as subsequent colonization, differentiations and
migrations overlaid upon previous population ranges. A total of 205
markers identified by denaturing high performance liquid
chromatography (DHPLC), together with 13 taken from the literature,
are used to construct a parsimonious genealogy. Ancestral allelic states
were deduced from orthologous great ape sequences. A total of 131
unique ecognize are defined which trace the micro evolutionary
trajectory of global modern human genetic diversification. The
genealogy provides a detailed phylogeographic portrait of contemporary
global population structure that is emblematic of human origins,
divergence and population history that is consistent with climatic, paleo-
anthropological and other genetic knowledge. The frequency of
occurrence of different ecognize can be used to distinguish
populations and to shed light on the sub-structures within a population,
also for inter and intra population variation studies. Population analyses
have examined allele frequencies at autosomal genetic markers (Cavalli-
Sforza As in this project, when a significant number of individuals in a
population et al., 1994). The incorporation of mitochondrial DNA during
the 1980s added a powerful tool to the geneticists’ tool kit, since mtDNA
does not recombine and is transmitted only through female germ line
(Stoneking and Soodyall, 1996). The increasing number of polymorphic
markers identified on the Y chromosome has allowed analyzing male
lineages, (Hammer and Zegura, 1997). A set of highly polymorphic
chromosome Y specific micro satellite became available for forensic,
population genetic and evolutionary studies. However, the lack of a
mutation frequency estimate for these loci prevents a reliable application.
MARKERS:
The human genome comprise of actually two genomes: a complex nuclear
genome, which account for 99.9995% of total genetic information and a
simple mitochondrial genome, which accounts for the remaining 0.0005%.
During zygote formation, a sperm cell contributes its nuclear genome, but
not its mitochondrial genome to the egg cell. Consequently, the
mitochondrial genome of the zygote is determined exclusively by that
originally found in the unfertilized egg. The mitochondrial genome is
therefore maternally inherited. As a result, it does not undergo any genetic
reshuffling and thus, is intact which makes it a unique tool for studying
human origins. Thus, everyone carries with them a more or less exact copy
of the mtDNA from their mother and their mother’s mother and so forth
for countless generations. The term “more or less exact” is the key to
scientist solving the mystery of human origins. That’s because like all
DNA, mtDNA is subject to random mutations over the eons. As these
mutations are passed on intact to next generation, they in effect become
“tracers” of family. A single type of circular double stranded molecule of
16,569 bases defines human mitochondrial genome.
MITOCHONDRIAL DNA (mtDNA) AS MARKER:
The mtDNA (Fig:1) has no repetitive DNA, spacers or introns. The
mtDNA contains 37 genes, all of which are involved in the production of
energy and its storage in ATP. It encodes 13 mRNAs, 22 tRNAs and 2
rRNAs. mtDNA has two strands, a guanine rich heavy (H) strand and a
cytosine rich light (L) strand. The heavy strand contains 12 of the 13-
polypeptide encoding genes, 14 of the 22 tRNA encoding genes and both