This is an accepted version of this page
121-544: Genetics and archaeogenetics of South Asia is the study of the genetics and archaeogenetics of the ethnic groups of South Asia . It aims at uncovering these groups' genetic histories . The geographic position of the Indian subcontinent makes its biodiversity important for the study of the early dispersal of anatomically modern humans across Asia . Based on mitochondrial DNA ( mtDNA ) variations, genetic unity across various South Asian subpopulations have shown that most of
242-429: A helical structure (i.e., shaped like a corkscrew). Their double-helix model had two strands of DNA with the nucleotides pointing inward, each matching a complementary nucleotide on the other strand to form what look like rungs on a twisted ladder. This structure showed that genetic information exists in the sequence of nucleotides on each strand of DNA. The structure also suggested a simple method for replication : if
363-534: A sexual process for transferring DNA from one cell to another cell (usually of the same species). Transformation requires the action of numerous bacterial gene products , and its primary adaptive function appears to be repair of DNA damages in the recipient cell. The diploid nature of chromosomes allows for genes on different chromosomes to assort independently or be separated from their homologous pair during sexual reproduction wherein haploid gametes are formed. In this way new combinations of genes can occur in
484-582: A DNA molecule. In 1983, Kary Banks Mullis developed the polymerase chain reaction , providing a quick way to isolate and amplify a specific section of DNA from a mixture. The efforts of the Human Genome Project , Department of Energy, NIH, and parallel private efforts by Celera Genomics led to the sequencing of the human genome in 2003. At its most fundamental level, inheritance in organisms occurs by passing discrete heritable units, called genes , from parents to offspring. This property
605-493: A complex trait is called heritability . Measurement of the heritability of a trait is relative—in a more variable environment, the environment has a bigger influence on the total variation of the trait. For example, human height is a trait with complex causes. It has a heritability of 89% in the United States. In Nigeria, however, where people experience a more variable access to good nutrition and health care , height has
726-483: A different parent. Many species have so-called sex chromosomes that determine the sex of each organism. In humans and many other animals, the Y chromosome contains the gene that triggers the development of the specifically male characteristics. In evolution, this chromosome has lost most of its content and also most of its genes, while the X chromosome is similar to the other chromosomes and contains many genes. This being said, Mary Frances Lyon discovered that there
847-546: A diploid cell with paired chromosomes. Diploid organisms form haploids by dividing, without replicating their DNA, to create daughter cells that randomly inherit one of each pair of chromosomes. Most animals and many plants are diploid for most of their lifespan, with the haploid form reduced to single cell gametes such as sperm or eggs . Although they do not use the haploid/diploid method of sexual reproduction, bacteria have many methods of acquiring new genetic information. Some bacteria can undergo conjugation , transferring
968-647: A distant positions, outside the main cluster. The most frequent mtDNA haplogroups in South Asia are M , R and U (where U is a descendant of R). Arguing for the longer term "rival Y-Chromosome model", Stephen Oppenheimer believes that it is highly suggestive that India is the origin of the Eurasian mtDNA haplogroups which he calls the "Eurasian Eves". According to Oppenheimer it is highly probable that nearly all human maternal lineages in Central Asia,
1089-429: A gene is used to produce a specific amino acid sequence . This process begins with the production of an RNA molecule with a sequence matching the gene's DNA sequence, a process called transcription . This messenger RNA molecule then serves to produce a corresponding amino acid sequence through a process called translation . Each group of three nucleotides in the sequence, called a codon , corresponds either to one of
1210-482: A heritability of only 62%. The molecular basis for genes is deoxyribonucleic acid (DNA). DNA is composed of deoxyribose (sugar molecule), a phosphate group, and a base (amine group). There are four types of bases: adenine (A), cytosine (C), guanine (G), and thymine (T). The phosphates make phosphodiester bonds with the sugars to make long phosphate-sugar backbones. Bases specifically pair together (T&A, C&G) between two backbones and make like rungs on
1331-435: A higher body temperature. In a low-temperature environment, however, the protein's structure is stable and produces dark-hair pigment normally. The protein remains functional in areas of skin that are colder—such as its legs, ears, tail, and face—so the cat has dark hair at its extremities. Environment plays a major role in effects of the human genetic disease phenylketonuria . The mutation that causes phenylketonuria disrupts
SECTION 10
#17327657501711452-506: A ladder. The bases, phosphates, and sugars together make a nucleotide that connects to make long chains of DNA. Genetic information exists in the sequence of these nucleotides, and genes exist as stretches of sequence along the DNA chain. These chains coil into a double a-helix structure and wrap around proteins called Histones which provide the structural support. DNA wrapped around these histones are called chromosomes. Viruses sometimes use
1573-505: A living cell or organism may increase or decrease gene transcription. A classic example is two seeds of genetically identical corn, one placed in a temperate climate and one in an arid climate (lacking sufficient waterfall or rain). While the average height the two corn stalks could grow to is genetically determined, the one in the arid climate only grows to half the height of the one in the temperate climate due to lack of water and nutrients in its environment. The word genetics stems from
1694-464: A mistaken alignment; this makes some regions in genomes more prone to mutating in this way. These errors create large structural changes in DNA sequence— duplications , inversions , deletions of entire regions—or the accidental exchange of whole parts of sequences between different chromosomes, chromosomal translocation . Ancient East Eurasians The term Ancient East Eurasian , alternatively also known as East Eurasian or Eastern Eurasian ,
1815-456: A phenotype involves studying identical and fraternal twins , or other siblings of multiple births . Identical siblings are genetically the same since they come from the same zygote. Meanwhile, fraternal twins are as genetically different from one another as normal siblings. By comparing how often a certain disorder occurs in a pair of identical twins to how often it occurs in a pair of fraternal twins, scientists can determine whether that disorder
1936-929: A population hub through a star-like expansion pattern (>45kya), and are linked to the "East Eurasian" lineage, broadly ancestral to modern populations in Eastern Eurasia, Oceania, and the Americas, notably East Asians , Southeast Asians , Indigenous Siberians , Aboriginal Australians , Papuans , Pacific Islanders , and mostly in Indigenous Americans , and partly in South Asians and Central Asians . While certain Initial Upper Paleolithic populations represented by specimens found in Central Asia and Europe , such as
2057-513: A proposed indigenous South Asian component (termed Ancient Ancestral South Indians , short "AASI") that is distantly related to the Andamanese peoples , as well as to East Asians and Aboriginal Australians , and further include additional, regionally variable East/Southeast Asians components. The proposed AASI type ancestry is closest to the non-West Eurasian part, termed S-component , extracted from South Asian samples, especially those from
2178-403: A series of genes can be combined to form a linear linkage map that roughly describes the arrangement of the genes along the chromosome. Genes express their functional effect through the production of proteins, which are molecules responsible for most functions in the cell. Proteins are made up of one or more polypeptide chains, each composed of a sequence of amino acids . The DNA sequence of
2299-457: A single parent. Offspring that are genetically identical to their parents are called clones . Eukaryotic organisms often use sexual reproduction to generate offspring that contain a mixture of genetic material inherited from two different parents. The process of sexual reproduction alternates between forms that contain single copies of the genome ( haploid ) and double copies ( diploid ). Haploid cells fuse and combine genetic material to create
2420-448: A small circular piece of DNA to another bacterium. Bacteria can also take up raw DNA fragments found in the environment and integrate them into their genomes, a phenomenon known as transformation . These processes result in horizontal gene transfer , transmitting fragments of genetic information between organisms that would be otherwise unrelated. Natural bacterial transformation occurs in many bacterial species, and can be regarded as
2541-400: A smooth blend of traits from their parents. Mendel's work provided examples where traits were definitely not blended after hybridization, showing that traits are produced by combinations of distinct genes rather than a continuous blend. Blending of traits in the progeny is now explained by the action of multiple genes with quantitative effects . Another theory that had some support at that time
SECTION 20
#17327657501712662-452: A transition of heredity from its status as myth to that of a scientific discipline, by providing a fundamental theoretical basis for genetics in the twentieth century. Other theories of inheritance preceded Mendel's work. A popular theory during the 19th century, and implied by Charles Darwin 's 1859 On the Origin of Species , was blending inheritance : the idea that individuals inherit
2783-412: A unique three-dimensional structure for that protein, and the three-dimensional structures of proteins are related to their functions. Some are simple structural molecules, like the fibers formed by the protein collagen . Proteins can bind to other proteins and simple molecules, sometimes acting as enzymes by facilitating chemical reactions within the bound molecules (without changing the structure of
2904-400: A variety of hereditary characteristics that replicate and remain active throughout generations. While haploid organisms have only one copy of each chromosome, most animals and many plants are diploid , containing two of each chromosome and thus two copies of every gene. The two alleles for a gene are located on identical loci of the two homologous chromosomes , each allele inherited from
3025-488: Is X-chromosome inactivation during reproduction to avoid passing on twice as many genes to the offspring. Lyon's discovery led to the discovery of X-linked diseases. When cells divide, their full genome is copied and each daughter cell inherits one copy. This process, called mitosis , is the simplest form of reproduction and is the basis for asexual reproduction. Asexual reproduction can also occur in multicellular organisms, producing offspring that inherit their genome from
3146-425: Is a somewhat ambiguous definition of what is referred to as a gene. Trait inheritance and molecular inheritance mechanisms of genes are still primary principles of genetics in the 21st century, but modern genetics has expanded to study the function and behavior of genes. Gene structure and function, variation, and distribution are studied within the context of the cell , the organism (e.g. dominance ), and within
3267-512: Is a sub-haplogroup of macrohaplogroup R. The distribution of haplogroup U is a mirror image of that for haplogroup M: the former has not been described so far among eastern Asians but is frequent in European populations as well as among South Asians. South Asian U lineages differ substantially from those in Europe and their coalescence to a common ancestor also dates back to about 50,000 years. It
3388-520: Is also found in SW Arabia. It is also found in Oman. The major South Asian Y-chromosome DNA haplogroups are H , J2 , L , R1a1 , R2 , which are commonly found among other West Eurasian populations, such as Middle Easterners or Europeans. Their geographical origins are listed as follows, according to the latest scholarship: H-L901 J-M172 L-M20 R- M417 R-M479 Haplogroup H (Y-DNA)
3509-482: Is caused by genetic or postnatal environmental factors. One famous example involved the study of the Genain quadruplets , who were identical quadruplets all diagnosed with schizophrenia . The genome of a given organism contains thousands of genes, but not all these genes need to be active at any given moment. A gene is expressed when it is being transcribed into mRNA and there exist many cellular methods of controlling
3630-504: Is estimated to have occurred slightly less than 50,000 years ago. In India, the major maternal lineages are various M subclades, followed by R and U sublineages. These mitochondrial haplogroups' coalescence times have been approximated to date to 50,000 BP. The major paternal lineages of South Asians are represented by the West Eurasian-affiliated haplogroups R1a1 , R2 , H , L and J2 . A minority belongs to
3751-507: Is found at a high frequency in South Asia and is considered to represent the major paternal lineage. H is today rarely found outside of South Asia, but is common among South Asian-descended populations, such as the Romanis , particularly the H-M82 subgroup. H was also found in some ancient samples of Europe and is still found today at a low frequency in certain southeastern Europeans and Arabs of
Genetics and archaeogenetics of South Asia - Misplaced Pages Continue
3872-464: Is found frequently among Burusho (approx. 12%) and Pashtuns (approx. 7%). Its highest frequency can be found in south western Balochistan province along the Makran coast (28%) to Indus River delta. L3a (PK3) is found in approximately 23% of Nuristani in northwest Pakistan . The clade is present in moderate distribution among the general Pakistani population (14% approx). In one study, 16% of
3993-630: Is of autochthonous South Asian origin. However, proposals for a Central Asian/Eurasian steppe origin for R1a1 are also quite common and supported by several more recent studies. Other minor haplogroups include subclades of Q-M242 , G-M201 , R1b , as well as Haplogroup C-M130 . Genetic studies comparing eight X chromosome based STR markers using a multidimensional scaling plot (MDS plot), revealed that modern-day South Asians like Indians, Pakistanis, Bangladeshis and Sinhalese people cluster close to each other, but also closer to Europeans . In contrast Southeast Asians, East Asians and Africans were placed at
4114-441: Is responsible for the development of structures within multicellular organisms, these patterns arise from the complex interactions between many cells. Within eukaryotes , there exist structural features of chromatin that influence the transcription of genes, often in the form of modifications to DNA and chromatin that are stably inherited by daughter cells. These features are called " epigenetic " because they exist "on top" of
4235-615: Is somewhat rarer in northern Indian castes (c. 5–6%). The presence of haplogroup L is quite rare among tribal groups (c. 5.6–7%); however, 14.6% has been observed among the Chenchus . Among regional and social groups, moderate to high frequencies have been observed in Jats (36.8%), Konkanastha Brahmins (18.6%), Lambadis (17.1%), Punjabis (12.1%) and Gujaratis (10.4%). In Pakistan, L1-M76 and L3-M357 subclades of L-M20 reach overall frequencies of 5.1% and 6.8%, respectively. Haplogroup L3 (M357)
4356-803: Is termed as the Indian Cline . The East Asian ancestry component forms the major ancestry among Tibeto-Burmese and Khasian speakers, and is generally restricted to the Himalayan foothills and Northeast India , with substantial presence also in Munda-speaking groups , as well as in some populations of northern, central and eastern South Asia. Modern South Asians are descendants of a combination of Western Eurasian ancestries (notably "Iran Neolithic Farmers" and " Western Steppe Herder " components) with an indigenous South Asian component (termed Ancient Ancestral South Indians , short "AASI") closest to
4477-497: Is the physical basis for inheritance: DNA replication duplicates the genetic information by splitting the strands and using each strand as a template for synthesis of a new partner strand. Genes are arranged linearly along long chains of DNA base-pair sequences. In bacteria , each cell usually contains a single circular genophore , while eukaryotic organisms (such as plants and animals) have their DNA arranged in multiple linear chromosomes. These DNA strands are often extremely long;
4598-694: Is the same as that which Mendel published. In his third law, he developed the basic principles of mutation (he can be considered a forerunner of Hugo de Vries ). Festetics argued that changes observed in the generation of farm animals, plants, and humans are the result of scientific laws. Festetics empirically deduced that organisms inherit their characteristics, not acquire them. He recognized recessive traits and inherent variation by postulating that traits of past generations could reappear later, and organisms could produce progeny with different attributes. These observations represent an important prelude to Mendel's theory of particulate inheritance insofar as it features
4719-601: Is the study of genes , genetic variation , and heredity in organisms . It is an important branch in biology because heredity is vital to organisms' evolution . Gregor Mendel , a Moravian Augustinian friar working in the 19th century in Brno , was the first to study genetics scientifically. Mendel studied "trait inheritance", patterns in the way traits are handed down from parents to offspring over time. He observed that organisms (pea plants) inherit traits by way of discrete "units of inheritance". This term, still used today,
4840-657: Is used in population genomics to describe the genetic ancestry and phylogenetic relationship of diverse populations primarily living in the Asia-Pacific region, belonging to the "Eastern Eurasian clade" of human genetic diversity , and which can be associated with the Initial Upper Paleolithic (IUP) wave, following the Out of Africa migration (>60kya). Modern humans of the Initial Upper Paleolithic wave (IUP) are suggested to have expanded from
4961-486: The Blue-eyed Mary ( Omphalodes verna ), for example, there exists a gene with alleles that determine the color of flowers: blue or magenta. Another gene, however, controls whether the flowers have color at all or are white. When a plant has two copies of this white allele, its flowers are white—regardless of whether the first gene has blue or magenta alleles. This interaction between genes is called epistasis , with
Genetics and archaeogenetics of South Asia - Misplaced Pages Continue
5082-675: The Eurasian Steppes or the Middle East and Caucasus region. The place of origin of these subclades plays a role in the debate about the origins of Indo-Europeans . In India , a high percentage of this haplogroup is observed in West Bengal Brahmins (72%) to the east, Gujarat Lohanas (60%) to the west, Khatris (67%) in the north, and Karnataka Medars (39%) in the south. It has also been found in several South Indian Dravidian -speaking tribals including
5203-626: The Indus Periphery Cline around ~5400–3700 BCE, which constitutes the main ancestral heritage of most modern South Asian groups. The Indus Periphery ancestry, around the 2nd millennium BCE, mixed with another West Eurasian wave, the incoming mostly male-mediated Yamnaya -Steppe component (archaeogenetically dubbed the Western Steppe Herders ) to form the Ancestral North Indians (ANI), while at
5324-611: The Indus Valley Civilisation . There are three subbranches of haplogroup L: L1-M76 (L1a1), L2-M317 (L1b) and L3-M357 (L1a2), found at varying levels in South Asia. Haplogroup L shows time of neolithic expansion. The clade is present in the Indian population at an overall frequency of c. 7–15%. Haplogroup L has a higher frequency among south Indian castes (c. 17–19%) and reaches 68% in some castes in Karnataka but
5445-602: The Irula tribe, and is generally found throughout all South Asian ethnic groups in varying degrees. The West Eurasian ancestry, which is closely related to Mesolithic hunter-gatherers and Neolithic farmers who lived on the Iranian Plateau (who are also closely related to Caucasus hunter-gatherers ), forms the major source of the South Asian genetic makeup, and combined with varying degrees of AASI ancestry, formed
5566-660: The Levant . Haplogroup H is frequently found among populations of India , Sri Lanka , Nepal , Bangladesh , Pakistan and the Maldives . All three branches of Haplogroup H (Y-DNA) are found in South Asia. Probable site of introduction; South Asia or West Asia or Southern Central Asia . It seems to represent the main Y-Chromosome haplogroup of the paleolithic inhabitants of South Asia and Europe respectively. Some individuals in South Asia have also been shown to belong to
5687-558: The Middle East , among the K-M9 descendants that migrated southwards from the Pamir Knot , and reached India c. 30,000 years ago. Other studies have proposed either a West Asian or South Asian origin for L-M20 and associated its expansion in the Indus valley (~7,000 YBP) to neolithic farmers. Genetic studies suggest that L-M20 may be one of the haplogroups of the original creators of
5808-497: The Oceania region, and may also harbor some small amounts of "xOoA" admixture from an earlier human dispersal, which did not contribute to any other human population. Alternatively, Australasians can be described as nearly equally admixture between a "Basal East Asian" source (represented by Tianyuan) and a deeper East Eurasian lineage not sampled yet. Traces of an unsampled deeply diverged East Eurasian lineage can be observed in
5929-495: The PCA compared to other South Asians. The Yamnaya or Western Steppe pastoralist component is found in higher frequency among Indo-Aryan speakers , and is distributed throughout the Indian subcontinent at lower frequency. Certain communities and caste groups from the northern Indian subcontinent display a peak of Western Steppe Herders ancestry at similar amounts as Northern Europeans. An East Asian-related ancestry component forms
6050-846: The Parsis at 38.89%, the Dravidian -speaking Brahuis at 28.18% and the Makrani Balochs at 24%. It also occurs at 18.18% in Makrani Siddis and at 3% in Karnataka Siddis . J2-M172 is found at an overall frequency of 10.3% among the Sinhalese people of Sri Lanka . In Maldives , 20.6% of Maldivian population were found to be haplogroup J2 positive. According to Dr. Spencer Wells , L-M20 originated either in India or
6171-554: The Persian Plateau . Major East Eurasian ancestry lineages which contributed to modern human populations include the following: The Australasian, Ancient Ancestral South Indian, and East and Southeast Asian lineages display a closer genetic relationship to each other than to any non-Asian lineages, and together represent the main branches of "Asian-related ancestry", which diverged from each other >40kya. The Australasian lineage however received higher archaic admixture in
SECTION 50
#17327657501716292-501: The Ust'-Ishim man , Bacho Kiro or Oase 2 , are inferred to have used inland routes, the ancestors of all modern East Eurasian populations are inferred to have used a Southern dispersal route through South Asia , where they subsequently diverged rapidly. Ancient East Eurasians diverged from Ancient West Eurasians around 46,000 years ago, and started to diversify themselves 45,000 years ago. This divergence most likely occurred in
6413-413: The ancient Greek γενετικός genetikos meaning "genitive"/"generative", which in turn derives from γένεσις genesis meaning "origin". The observation that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding . The modern science of genetics, seeking to understand this process, began with
6534-415: The neutral theory of molecular evolution through publishing the nearly neutral theory of molecular evolution . In this theory, Ohta stressed the importance of natural selection and the environment to the rate at which genetic evolution occurs. One important development was chain-termination DNA sequencing in 1977 by Frederick Sanger . This technology allows scientists to read the nucleotide sequence of
6655-603: The Austroasiatic language speaking people admixed with Indian population about 2000–3800 years ago, which may suggest arrival of Southeast Asian genetic component in the area. It has been found that the ancestral node of the phylogenetic tree of all the mtDNA types ( mitochondrial DNA haplogroups ) typically found in Central Asia, the West Asia and Europe are also to be found in South Asia at relatively high frequencies. The inferred divergence of this common ancestral node
6776-421: The DNA sequence and retain inheritance from one cell generation to the next. Because of epigenetic features, different cell types grown within the same medium can retain very different properties. Although epigenetic features are generally dynamic over the course of development, some, like the phenomenon of paramutation , have multigenerational inheritance and exist as rare exceptions to the general rule of DNA as
6897-502: The East Eurasian-affiliated Haplogroup O-M175 . O-M175 is mainly restricted to Austroasiatic and Tibeto-Burmese speakers, and also common among East and Southeast Asians, while H is largely restricted to South Asians and R1a1, J2 and L as well as a subclade of H (H2) are commonly found among European and Middle Eastern populations. Some researchers have argued that Y-DNA Haplogroup R1a1 (M17)
7018-632: The F1 offspring mate with each other, the offspring are called the "F2" (second filial) generation. One of the common diagrams used to predict the result of cross-breeding is the Punnett square . When studying human genetic diseases, geneticists often use pedigree charts to represent the inheritance of traits. These charts map the inheritance of a trait in a family tree. Organisms have thousands of genes, and in sexually reproducing organisms these genes generally assort independently of each other. This means that
7139-504: The Greek word genesis —γένεσις, "origin", predates the noun and was first used in a biological sense in 1860. Bateson both acted as a mentor and was aided significantly by the work of other scientists from Newnham College at Cambridge, specifically the work of Becky Saunders , Nora Darwin Barlow , and Muriel Wheldale Onslow . Bateson popularized the usage of the word genetics to describe
7260-555: The Johannes Gutenberg University Mainz (JGU), the main ancestry component of South Asians is derived from a population related to Neolithic farmers from the eastern Fertile Crescent and Iran . In the 2nd millennium BCE, the Indus Periphery -related ancestry mixed with the arriving Yamnaya-Steppe component forming the Ancestral North Indians (ANI), while at the same time it contributed to
7381-523: The Kotas (41%) of Tamil Nadu, Chenchu (26%) and Valmikis of Andhra Pradesh as well as the Yadav and Kallar of Tamil Nadu suggesting that M17 is widespread in these southern Indians tribes. Besides these, studies show high percentages in regionally diverse groups such as Manipuris (50%) to the extreme northeast and in among Punjabis (47%) to the extreme northwest. In Pakistan, it is found at 71% among
SECTION 60
#17327657501717502-630: The Middle East and Europe descended from only four mtDNA lines that originated in South Asia 50,000–100,000 years ago. The macrohaplogroup M , which is considered as a cluster of the proto-Asian maternal lineages, represents more than 60% of South Asian MtDNA. The M macrohaplotype in India includes many subgroups that differ profoundly from other sublineages in East Asia especially Mongoloid populations. The deep roots of M phylogeny clearly ascertain
7623-726: The Mohanna of Sindh Province to the south and 46% among the Baltis of Gilgit-Baltistan to the north. 23% of the Sinhalese people out of a sample of 87 subjects were found to be R1a1a (R-SRY1532) positive according to a 2003 research, while another research in the same year found 12.8% of 38 samples belonged to this specific haplogroup. In the Maldives , 23.8% of the Maldivian people were found to be R1a1a (M17) positive. People in Terai region, Nepal show R1a1a at 69%. In South Asia,
7744-724: The Sinhalese were found to be Haplogroup L-M20 positive. In another study 18% were found to belong to L1. In South Asia, R1a1 has been observed often with high frequency in a number of demographic groups, as well as with highest STR diversity which lead some to see it as the locus of origin. While R1a originated c. 22,000 to 25,000 years ago, its subclade M417 (R1a1a1) diversified c. 5,800 years ago. The distribution of M417-subclades R1-Z282 (including R1-Z280) in Central and Eastern Europe and R1-Z93 in Asia suggests that R1a1a diversified within
7865-533: The South Asian subtypes of haplogroup M, which indicates that no large-scale migration from the present Turkic -speaking populations of Central Asia occurred to India. The absence of haplogroup M in Europeans, compared to its equally high frequency among South Asians, East Asians and in some Central Asian populations contrasts with the Western Eurasian leanings of South Asian paternal lineages. Most of
7986-713: The South Indian hill tribe Toda at 38.46%, in the Andh tribe of Telangana at 35.19% and in the Kol tribe of Uttar Pradesh at a frequency of 33.34%. Haplogroup J-P209 was found to be more common in India's Shia Muslims , of which 28.7% belong to haplogroup J, with 13.7% in J-M410, 10.6% in J-M267 and 4.4% in J2b. In Pakistan , the highest frequencies of J2-M172 were observed among
8107-448: The ability of the body to break down the amino acid phenylalanine , causing a toxic build-up of an intermediate molecule that, in turn, causes severe symptoms of progressive intellectual disability and seizures. However, if someone with the phenylketonuria mutation follows a strict diet that avoids this amino acid, they remain normal and healthy. A common method for determining how genes and environment ("nature and nurture") contribute to
8228-444: The adaptive function of repair of DNA damages. The first cytological demonstration of crossing over was performed by Harriet Creighton and Barbara McClintock in 1931. Their research and experiments on corn provided cytological evidence for the genetic theory that linked genes on paired chromosomes do in fact exchange places from one homolog to the other. The probability of chromosomal crossover occurring between two given points on
8349-464: The ancestral nodes of the phylogenetic tree of all the mtDNA types originated in the subcontinent. Conclusions of studies based on Y chromosome variation and autosomal DNA variation have been varied. The genetic makeup of modern South Asians can be described at the deepest level as a combination of West Eurasian (related to ancient and modern people in Europe and West Asia ) ancestries with divergent East Eurasian ancestries . The latter primarily include
8470-440: The basis for inheritance. During the process of DNA replication, errors occasionally occur in the polymerization of the second strand. These errors, called mutations, can affect the phenotype of an organism, especially if they occur within the protein coding sequence of a gene. Error rates are usually very low—1 error in every 10–100 million bases—due to the "proofreading" ability of DNA polymerases . Processes that increase
8591-404: The cat plays the role of the environment. The cat's genes code for dark hair, thus the hair-producing cells in the cat make cellular proteins resulting in dark hair. But these dark hair-producing proteins are sensitive to temperature (i.e. have a mutation causing temperature-sensitivity) and denature in higher-temperature environments, failing to produce dark-hair pigment in areas where the cat has
8712-429: The cell, these genes for tryptophan synthesis are no longer needed. The presence of tryptophan directly affects the activity of the genes—tryptophan molecules bind to the tryptophan repressor (a transcription factor), changing the repressor's structure such that the repressor binds to the genes. The tryptophan repressor blocks the transcription and expression of the genes, thereby creating negative feedback regulation of
8833-421: The chromosome is related to the distance between the points. For an arbitrarily long distance, the probability of crossover is high enough that the inheritance of the genes is effectively uncorrelated. For genes that are closer together, however, the lower probability of crossover means that the genes demonstrate genetic linkage; alleles for the two genes tend to be inherited together. The amounts of linkage between
8954-422: The combined DNA sequences of all chromosomes) is called the genome . DNA is most often found in the nucleus of cells, but Ruth Sager helped in the discovery of nonchromosomal genes found outside of the nucleus. In plants, these are often found in the chloroplasts and in other organisms, in the mitochondria. These nonchromosomal genes can still be passed on by either partner in sexual reproduction and they control
9075-486: The context of a population. Genetics has given rise to a number of subfields, including molecular genetics , epigenetics , and population genetics . Organisms studied within the broad field span the domains of life ( archaea , bacteria , and eukarya ). Genetic processes work in combination with an organism's environment and experiences to influence development and behavior , often referred to as nature versus nurture . The intracellular or extracellular environment of
9196-417: The expression of genes such that proteins are produced only when needed by the cell. Transcription factors are regulatory proteins that bind to DNA, either promoting or inhibiting the transcription of a gene. Within the genome of Escherichia coli bacteria, for example, there exists a series of genes necessary for the synthesis of the amino acid tryptophan . However, when tryptophan is already available to
9317-708: The extant mtDNA boundaries in South and Southwest Asia were likely shaped during the initial settlement of Eurasia by anatomically modern humans. The macrohaplogroup R (a very large and old subdivision of macrohaplogroup N ) is also widely represented and accounts for the other 40% of South Asian MtDNA. A very old and most important subdivision of it is haplogroup U that, while also present in West Eurasia , has several subclades specific to South Asia. Most important South Asian haplogroups within R: Haplogroup U
9438-557: The formation of Ancestral South Indians (ASI) by admixture with hunter-gatherers further South having higher proportions of AASI-related ancestry. The proximity to West Eurasian populations is based on the ANI-ASI gradient, also termed the Indian Cline , with the groups harboring higher ANI-ancestry being closer to West Eurasians as compared to populations harboring higher ASI-ancestry. Tribal groups from southern India harbor mostly ASI ancestry and sits farthest from West Eurasian groups on
9559-596: The frequency of R2 and R2a lineage is around 10–15% in India and Sri Lanka and 7–8% in Pakistan. At least 90% of R-M124 individuals are located in South Asia. It is also reported in Caucasus and Central Asia at a lower frequency. A genetic study by Mondal et al. in 2017 concluded that Haplogroup R2 originated in northern India and was already present before the Steppe migration. Genetics Genetics
9680-483: The genome of ancient and modern inhabitants of the Tibetan Plateau . While modern Tibetans mostly derive their ancestry from a northern East Asian source (specifically Yellow River farmers), a minor, but significant contribution stems from a deeply diverged East Eurasian local " Ghost population " that was distinct from other deeply diverged lineages such as Ust'Ishim, Hoabinhian/Onge or Tianyuan, representing
9801-469: The information an organism uses to function, the environment plays an important role in determining the ultimate phenotypes an organism displays. The phrase " nature and nurture " refers to this complementary relationship. The phenotype of an organism depends on the interaction of genes and the environment. An interesting example is the coat coloration of the Siamese cat . In this case, the body temperature of
9922-406: The inheritance of an allele for yellow or green pea color is unrelated to the inheritance of alleles for white or purple flowers. This phenomenon, known as " Mendel's second law " or the "law of independent assortment," means that the alleles of different genes get shuffled between parents to form offspring with many different combinations. Different genes often interact to influence the same trait. In
10043-427: The largest human chromosome, for example, is about 247 million base pairs in length. The DNA of a chromosome is associated with structural proteins that organize, compact, and control access to the DNA, forming a material called chromatin ; in eukaryotes, chromatin is usually composed of nucleosomes , segments of DNA wound around cores of histone proteins. The full set of hereditary material in an organism (usually
10164-581: The local Paleolithic population of the Tibetan Plateau. Deeper IUP-associated East Eurasian lineages have been associated with the remains of the Ust'-Ishim man from Siberia, and the Oase and Bacho Kiro cave specimens in southeastern Europe, and represent early inland migrations, deeply diverged from all other East Eurasian populations. These deep East Eurasian populations did not contribute to later Eurasian populations, except small contributions to
10285-649: The main West Eurasian geneflow event happened during the Neolithic period , or already during the Holocene (pre-Neolithic period). There is also evidence that some West Eurasian like ancestry reached South Asia earlier, during the Upper Paleolithic (around 40,000–30,000 years BCe)." The Neolithic or Pre-Neolithic Iranian lineage, which may be associated with the spread of Dravidian languages , forms
10406-587: The major ancestry among Tibeto-Burmese and Khasi an speakers in the Himalayan foothills and Northeast India , and is also found in substantial presence in Mundari-speaking groups . According to Zhang et al., Austroasiatic migrations from Southeast Asia into India took place after the last Glacial maximum, circa 10,000 years ago. Arunkumar et al. suggest Austroasiatic migrations from Southeast Asia occurred into Northeast India 5.2 ± 0.6 kya and into East India 4.3 ± 0.2 kya. Tätte et al. 2019 estimated that
10527-676: The major source of the South Asian gene pool, and contributed foundational to all modern South Asians. Paired with varying degrees of AASI admixture, the Ancient Iranian lineage gave rise to the Indus Periphery Cline , which is characteristic for modern South Asians and central in the South Asian genetic heritage. Genetic data suggests that the specific Ancient Iranian-related lineage, diverged from Neolithic Iranian plateau lineages more than 10,000 years ago. According to an international research team led by palaeogeneticists of
10648-609: The much rarer subclade H3 (Z5857). Haplogroup H is by no means restricted to specific populations. For example, H is possessed by about 28.8% of Indo-Aryan castes. and in tribals about 25–35%. Haplogroup J2 has been present in South Asia mostly as J2a-M410 and J2b-M102, since neolithic times (9500 YBP). J2 clades attain peak frequencies in the North-West and South India and is found at 19% within South Indian castes, 11% in North Indian castes and 12% in Pakistan. In South India ,
10769-571: The nature of inheritance in plants. In his paper " Versuche über Pflanzenhybriden " (" Experiments on Plant Hybridization "), presented in 1865 to the Naturforschender Verein (Society for Research in Nature) in Brno , Mendel traced the inheritance patterns of certain traits in pea plants and described them mathematically. Although this pattern of inheritance could only be observed for a few traits, Mendel's work suggested that heredity
10890-491: The non-West Eurasian-related component in the " qpAdm " admixture-modelling of an IVC -related individual (labelled "I6113") because both populations "have the same phylogenetic relationship to the non-West Eurasian-related of I6113 likely due to shared ancestry deeply in time". According to Yang (2022): This distinct South Asian ancestry, denoted as the Ancient Ancestral South Indian (AASI) lineage,
11011-444: The non–West Eurasian part extracted from South Asian samples; distantly related to the Andamanese peoples , as well as to East Asians and Aboriginal Australians , as well as regional variable additional East/Southeast Asian components respectively. The proposed AASI lineage, which is hypothesized to represent the ancestry of the very first hunter-gatherers and peoples of the Indian subcontinent, formed around ~40,000 years BCe . It
11132-500: The offspring of a mating pair. Genes on the same chromosome would theoretically never recombine. However, they do, via the cellular process of chromosomal crossover . During crossover, chromosomes exchange stretches of DNA, effectively shuffling the gene alleles between the chromosomes. This process of chromosomal crossover generally occurs during meiosis , a series of cell divisions that creates haploid cells. Meiotic recombination , particularly in microbial eukaryotes , appears to serve
11253-435: The original sequence. A particularly important source of DNA damages appears to be reactive oxygen species produced by cellular aerobic respiration , and these can lead to mutations. In organisms that use chromosomal crossover to exchange DNA and recombine genes, errors in alignment during meiosis can also cause mutations. Errors in crossover are especially likely when similar sequences cause partner chromosomes to adopt
11374-470: The phenotype of the organism, while the other allele is called recessive as its qualities recede and are not observed. Some alleles do not have complete dominance and instead have incomplete dominance by expressing an intermediate phenotype, or codominance by expressing both alleles at once. When a pair of organisms reproduce sexually , their offspring randomly inherit one of the two alleles from each parent. These observations of discrete inheritance and
11495-533: The presence of J2 is higher among middle castes at 21%, followed by upper castes at 18.6% and lower castes at 14%. Among caste groups, the highest frequency of J2-M172 is observed among Tamil Vellalars of South India, at 38.7%. J2 is present in tribals too and has a frequency of 11% in Austro-Asiatic tribals. Among the Austro-Asiatic tribals, the predominant J2 occurs in the Lodha (35%). J2 is also present in
11616-543: The process of protein production . It was discovered that the cell uses DNA as a template to create matching messenger RNA , molecules with nucleotides very similar to DNA. The nucleotide sequence of a messenger RNA is used to create an amino acid sequence in protein; this translation between nucleotide sequences and amino acid sequences is known as the genetic code . With the newfound molecular understanding of inheritance came an explosion of research. A notable theory arose from Tomoko Ohta in 1973 with her amendment to
11737-435: The product rule, the sum rule, and more. Geneticists use diagrams and symbols to describe inheritance. A gene is represented by one or a few letters. Often a "+" symbol is used to mark the usual, non-mutant allele for a gene. In fertilization and breeding experiments (and especially when discussing Mendel's laws) the parents are referred to as the "P" generation and the offspring as the "F1" (first filial) generation. When
11858-519: The properties of a protein by destabilizing the structure or changing the surface of the protein in a way that changes its interaction with other proteins and molecules. For example, sickle-cell anemia is a human genetic disease that results from a single base difference within the coding region for the β-globin section of hemoglobin, causing a single amino acid change that changes hemoglobin's physical properties. Sickle-cell versions of hemoglobin stick to themselves, stacking to form fibers that distort
11979-426: The protein itself). Protein structure is dynamic; the protein hemoglobin bends into slightly different forms as it facilitates the capture, transport, and release of oxygen molecules within mammalian blood. A single nucleotide difference within DNA can cause a change in the amino acid sequence of a protein. Because protein structures are the result of their amino acid sequences, some changes can dramatically change
12100-406: The rate of changes in DNA are called mutagenic : mutagenic chemicals promote errors in DNA replication, often by interfering with the structure of base-pairing, while UV radiation induces mutations by causing damage to the DNA structure. Chemical damage to DNA occurs naturally as well and cells use DNA repair mechanisms to repair mismatches and breaks. The repair does not, however, always restore
12221-664: The relatively most closely related modern populations to the AASI component and henceforth used as an (imperfect) proxy for it, but others (Yelmen et al. 2019) note that both are deeply diverged from each other, and propose the Southern Indian tribal groups, such as Paniya and Irula as better proxies for indigenous South Asian (AASI) ancestry, although noting that these tribal groups also carry varying degrees of Ancient Iranian admixture. Shinde et al. 2019 noted that both Andamanese Onge or East Siberian groups can be used as proxy for
12342-477: The relic of South Asian lineages as compared to other M sublineages (in East Asia and elsewhere) suggesting 'in-situ' origin of these sub-haplogroups in South Asia, most likely in India. These deep-rooting lineages are not language specific and spread over all the language groups in India. Virtually all modern Central Asian MtDNA M lineages seem to belong to the Eastern Eurasian ( Mongolian ) rather than
12463-408: The same allele of a given gene are called homozygous at that gene locus , while organisms with two different alleles of a given gene are called heterozygous . The set of alleles for a given organism is called its genotype , while the observable traits of the organism are called its phenotype . When organisms are heterozygous at a gene, often one allele is called dominant as its qualities dominate
12584-501: The same time it contributed to the formation of Ancestral South Indians (ASI) by admixture with hunter-gatherers having higher proportions of AASI-related ancestry. The ANI-ASI gradient, as demonstrated by the higher proportion of ANI in traditionally upper caste and Indo-European speakers, that resulted because of the admixture between the ANI and the ASI after 2000 BCE at various proportions
12705-401: The second gene epistatic to the first. Many traits are not discrete features (e.g. purple or white flowers) but are instead continuous features (e.g. human height and skin color ). These complex traits are products of many genes. The influence of these genes is mediated, to varying degrees, by the environment an organism has experienced. The degree to which an organism's genes contribute to
12826-509: The segregation of alleles are collectively known as Mendel's first law or the Law of Segregation. However, the probability of getting one gene over the other can change due to dominant, recessive, homozygous, or heterozygous genes. For example, Mendel found that if you cross heterozygous organisms your odds of getting the dominant trait is 3:1. Real geneticist study and calculate probabilities by using theoretical probabilities, empirical probabilities,
12947-653: The shape of red blood cells carrying the protein. These sickle-shaped cells no longer flow smoothly through blood vessels , having a tendency to clog or degrade, causing the medical problems associated with this disease. Some DNA sequences are transcribed into RNA but are not translated into protein products—such RNA molecules are called non-coding RNA . In some cases, these products fold into structures which are involved in critical cell functions (e.g. ribosomal RNA and transfer RNA ). RNA can also have regulatory effects through hybridization interactions with other RNA molecules (such as microRNA ). Although genes contain all
13068-446: The similar molecule RNA instead of DNA as their genetic material. DNA normally exists as a double-stranded molecule, coiled into the shape of a double helix . Each nucleotide in DNA preferentially pairs with its partner nucleotide on the opposite strand: A pairs with T, and C pairs with G. Thus, in its two-stranded form, each strand effectively contains all necessary information, redundant with its partner strand. This structure of DNA
13189-500: The single celled alga Acetabularia . The Hershey–Chase experiment in 1952 confirmed that DNA (rather than protein) is the genetic material of the viruses that infect bacteria, providing further evidence that DNA is the molecule responsible for inheritance. James Watson and Francis Crick determined the structure of DNA in 1953, using the X-ray crystallography work of Rosalind Franklin and Maurice Wilkins that indicated DNA has
13310-441: The strands are separated, new partner strands can be reconstructed for each based on the sequence of the old strand. This property is what gives DNA its semi-conservative nature where one strand of new DNA is from an original parent strand. Although the structure of DNA showed how inheritance works, it was still not known how DNA influences the behavior of cells. In the following years, scientists tried to understand how DNA controls
13431-580: The study of inheritance in his inaugural address to the Third International Conference on Plant Hybridization in London in 1906. After the rediscovery of Mendel's work, scientists tried to determine which molecules in the cell were responsible for inheritance. In 1900, Nettie Stevens began studying the mealworm. Over the next 11 years, she discovered that females only had the X chromosome and males had both X and Y chromosomes. She
13552-536: The tryptophan synthesis process. Differences in gene expression are especially clear within multicellular organisms , where cells all contain the same genome but have very different structures and behaviors due to the expression of different sets of genes. All the cells in a multicellular organism derive from a single cell, differentiating into variant cell types in response to external and intercellular signals and gradually establishing different patterns of gene expression to create different behaviors. As no single gene
13673-482: The twenty possible amino acids in a protein or an instruction to end the amino acid sequence ; this correspondence is called the genetic code . The flow of information is unidirectional: information is transferred from nucleotide sequences into the amino acid sequence of proteins, but it never transfers from protein back into the sequence of DNA—a phenomenon Francis Crick called the central dogma of molecular biology . The specific sequence of amino acids results in
13794-545: The two is responsible for inheritance. In 1928 , Frederick Griffith discovered the phenomenon of transformation : dead bacteria could transfer genetic material to "transform" other still-living bacteria. Sixteen years later, in 1944, the Avery–MacLeod–McCarty experiment identified DNA as the molecule responsible for transformation. The role of the nucleus as the repository of genetic information in eukaryotes had been established by Hämmerling in 1943 in his work on
13915-538: The work of the Augustinian friar Gregor Mendel in the mid-19th century. Prior to Mendel, Imre Festetics , a Hungarian noble, who lived in Kőszeg before Mendel, was the first who used the word "genetic" in hereditarian context, and is considered the first geneticist. He described several rules of biological inheritance in his work The genetic laws of nature (Die genetischen Gesetze der Natur, 1819). His second law
14036-518: Was able to conclude that sex is a chromosomal factor and is determined by the male. In 1911, Thomas Hunt Morgan argued that genes are on chromosomes , based on observations of a sex-linked white eye mutation in fruit flies . In 1913, his student Alfred Sturtevant used the phenomenon of genetic linkage to show that genes are arranged linearly on the chromosome. Although genes were known to exist on chromosomes, chromosomes are composed of both protein and DNA, and scientists did not know which of
14157-591: Was first observed by Gregor Mendel, who studied the segregation of heritable traits in pea plants, showing for example that flowers on a single plant were either purple or white—but never an intermediate between the two colors. The discrete versions of the same gene controlling the inherited appearance (phenotypes) are called alleles . In the case of the pea, which is a diploid species, each individual plant has two copies of each gene, one copy inherited from each parent. Many species, including humans, have this pattern of inheritance. Diploid organisms with two copies of
14278-426: Was found that the AASI are distinct from Western Eurasian groups and have a closer genetic affinity with Ancient East Eurasians (such as Andamanese Onge or East Asian peoples). Based on this, it has been inferred that the AASI lineage diverged from other Eastern Eurasian lineages, such as 'Australasians' and ' East/Southeast Asian people ', during their dispersal using a Southern route . The Andamanese people are among
14399-517: Was only found in a small percentage of ancient and present-day South Asians. Present-day Onge from the Andamanese Islands are the best reference population to date, but Narasimhan et al. used qpGraph to show that the divergence between the AASI lineage and the ancestry found in present-day Onge was very deep. Ancestry associated with the AASI lineage was found at low levels in almost all present-day Indian populations. Genetic data shows that
14520-421: Was particulate, not acquired, and that the inheritance patterns of many traits could be explained through simple rules and ratios. The importance of Mendel's work did not gain wide understanding until 1900, after his death, when Hugo de Vries and other scientists rediscovered his research. William Bateson , a proponent of Mendel's work, coined the word genetics in 1905. The adjective genetic , derived from
14641-529: Was the inheritance of acquired characteristics : the belief that individuals inherit traits strengthened by their parents. This theory (commonly associated with Jean-Baptiste Lamarck ) is now known to be wrong—the experiences of individuals do not affect the genes they pass to their children. Other theories included Darwin's pangenesis (which had both acquired and inherited aspects) and Francis Galton 's reformulation of pangenesis as both particulate and inherited. Modern genetics started with Mendel's studies of
#170829