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In the study of molecular evolution, a haplogroup (from the , haploûs, "onefold, single, simple") is a group of similar haplotypes that share a common ancestor with a single nucleotide polymorphism (SNP) mutation. Because a haplogroup consists of similar haplotypes, this is what makes it possible to predict a haplogroup from haplotypes. An SNP test confirms a haplogroup. Haplogroups are assigned letters of the alphabet, and refinements consist of additional number and letter combinations, for example R1b1. Y-chromosome and mitochondrial DNA haplogroups have different haplogroup designations. Haplogroups pertain to deep ancestral origins dating back thousands of years.

In human genetics, the haplogroups most commonly studied are Y-chromosome haplogroups and mitochondrial DNA haplogroups, both of which can be used to define genetic populations. Y-DNA is passed solely along the patrilineal line, from father to son, while mtDNA is passed down the matrilineal line, from mother to daughter. Neither recombines, and thus Y-DNA and mtDNA change only by chance mutation at each generation with no intermixture between parents' genetic material.

Haplogroup formation

Mitochondria are small organelles that lie in the cytoplasm of eucaryotic cells, such as those of humans. Their primary purpose is to provide energy to the cell. Mitochondria are thought to be the vestigial remains of symbiotic bacteria that were once free living. One indication that mitochondria were once free living is that they contain a relatively small circular segment of DNA, called mitochondrial DNA (mtDNA). The overwhelming majority of a human's DNA is contained in chromosomes in the nucleus of the cell, but mtDNA is an exception. An individual inherits their cytoplasm and the organelles it contains exclusively from their mother, as these are derived from the ovum (egg cell), sperm only carry chromosomal DNA due to the necessity of maintaining motility. When a mutation arises in mtDNA molecule, the mutation is therefore passed in a direct female line of descent. These mutations are derived from copying mistakes, when the DNA is copied it is possible that a single mistake occurs in the DNA sequence, these single mistakes are called single nucleotide polymorphisms (SNPs).

Human Y chromosomes are male-specific sex chromosomes; nearly all humans that possess a Y chromosome will be morphologically male. Y chromosomes are therefore passed from father to son; although Y chromosomes are situated in the cell nucleus, they only recombine with the X chromosome at the ends of the Y chromosome; the vast majority of the Y chromosome (95%) does not recombine. When mutations (SNPs) arise in the Y chromosome, they are passed on directly from father to son in a direct male line of descent. The Y chromosome and mtDNA therefore share specific properties.

Other chromosomes, autosomes and X chromosomes in women, share their genetic material (called crossing over leading to recombination) during meiosis (a special type of cell division that occurs for the purposes of sexual reproduction). Effectively this means that the genetic material from these chromosomes gets mixed up in every generation, and so any new mutations are passed down randomly from parents to offspring.

The special feature that both Y chromosomes and mtDNA display is that mutations can accrue along a certain segment of both molecules and these mutations remain fixed in place on the DNA. Furthermore the historical sequence of these mutations can also be inferred. For example, if a set of ten Y chromosomes (derived from ten different men) contains a mutation, A, but only five of these chromosomes contain a second mutation, B, it must be the case that mutation B occurred after mutation A. Furthermore all ten men who carry the chromosome with mutation A are the direct male line descendants of the same man who was the first person to carry this mutation. The first man to carry mutation B was also a direct male line descendant of this man, but is also the direct male line ancestor of all men carrying mutation B. Series of mutations such as this form molecular lineages. Furthermore each mutation defines a set of specific Y chromosomes called a haplogroup. All men carrying mutation A form a single haplogroup, all men carrying mutation B are part of this haplogroup, but mutation B also defines a more recent haplogroup (which is a subgroup or subclade) of its own which men carrying only mutation A do not belong to. Both mtDNA and Y chromosomes are grouped into lineages and haplogroups; these are often presented as tree like diagrams.

Haplogroup population genetics

It is usually assumed that there is little natural selection for or against a particular haplotype mutation which has survived to the present day, so apart from mutation rates (which may vary from one marker to another) the main driver of population genetics affecting the proportions of haplotypes in a population is genetic drift — random fluctuation caused by the sampling randomness of which members of the population happen to pass their DNA on to members of the next generation of the appropriate sex. This causes the prevalence of a particular marker in a population to continue to fluctuate, until it either hits 100%, or falls out of the population entirely. In a large population with efficient mixing the rate of genetic drift for common alleles is very low; however, in a very small interbreeding population the proportions can change much more quickly. The marked geographical variations and concentrations of particular haplotypes and groups of haplotypes therefore witness the distinctive effects of repeated population bottlenecks or founder events followed by population separations and increases.The lineages which can be traced back from the present will not reflect the full genetic variation of the older population: genetic drift means that some of the variants will have died out. The cost of full mtDNA sequence tests has limited the availability of data. Haplotype coalescence times and current geographical prevalences both carry considerable error uncertainties.

Human Y-chromosome DNA haplogroups

Human Y chromosome DNA (Y-DNA) haplogroups are lettered A through T, and are further subdivided using numbers and lower case letters. Y chromosome haplogroup designations are established by the Y Chromosome Consortium.

Y-chromosomal Adam is the name given by researchers to the male who is the most recent common patrilineal ancestor of all living humans.

Major Y-chromosome haplogroups, and their geographical regions of occurrence (prior tothe recent European colonization), include:



Groups without mutation M168





Groups with mutation M168

(mutation M168 occurred ~50,000 bp)

  • Haplogroup C (M130) (Oceania, North/Central/East Asia, North America and significant presence in India)
  • Haplogroup F (M89) Oceania, Europe, Asia, North- and South- America
  • YAP+ haplogroups


Groups with mutation M89

(mutation M89 occurred ~45,000 bp)

  • Haplogroup F (P14, M213) (southern India, Sri Lanka, China, Korea)


  • Haplogroup G (M201) (present among many ethnic groups in Eurasia, usually at low frequency; most common in the Caucasus, the Iranian plateau, and Anatolia; in Europe mainly in Italy, Greece, northern Spain, the Tyrol, as well as Bohemia, Moravia; Britain and Norway at only 2%)


  • Haplogroup H (M69) (India, Sri Lanka, Nepal, and at low frequency in Pakistan, Iran, Central Asia, and Arabia)




Groups with mutations L15 & L16



Groups with mutation M9

(mutation M9 occurred ~40,000 bp)



Groups with mutation rs2033003


Groups with mutation M230
  • Haplogroup S (New Guinea); formerly known as Haplogroup K5


Groups with mutation M70
  • Haplogroup T - (North Africa, Horn of Africa, Southwest Asia, the Mediterranean, South Asia); formerly known as Haplogroup K2


Human mitochondrial DNA haplogroups

Human mtDNA haplogroups are lettered:A,B,C,CZ,D,E,F,G,H,pre-HV,HV,I,J,pre-JT,JT,K,L0,L1,L2,L3,L4,L5,L6,L7,M,N,P,Q,R,S,T,U,UK,V,W,X,Y, andZ.

Mitochondrial Eve is the name given by researchers to the woman who is the most recent common matrilineal ancestor of all living humans.

Defining populations

Haplogroups can be used to define genetic populations and are often geographically oriented. For example, the following are common divisions for mtDNA haplogroups:

  • Sub-Saharan African: L0, L1, L2, L3, L4, L5, L6, L7
  • West Eurasian: H, T, U, V, X, K, I, J, W (all listed West Eurasian haplogroups are derived from macro-haplogroup N)
  • East Eurasian: A, B, C, D, E, F, G, Y (note: C, D, E, and G belong to macro-haplogroup M)
  • Native American: A, B, C, D, X
  • Australo-Melanesian: P, Q, S


The mitochondrial haplogroups are divided into3 main groups, which are designated by the 3 sequential letters L, M, N.Humanity first split within the L group between L0 and L1. L1 gave rise to other L groups, one of which, L3, split into the M and N group. The M group comprises the first wave of human migration out of Africa, following an eastward route along southern coastal areas. Descendent populations belonging to haplogroup M are found throughout East Africa, Asia, the Americas, and Melanesia, though almost none have been found in Europe. The N group may represent another migration out of Africa, heading northward instead of eastward. Shortly after the migration, the large R group split off from the N. Haplogroup R consists of two subgroups defined on the basis of their geographical distributions, one found in southeastern Asia and Oceania and the other containing almost all of the modern European populations. Haplogroup N(xR), i.e. mtDNA that belongs to the N group but not to its R subgroup, is typical of Australian aboriginal populations, while also being present at low frequencies among many populations of Eurasia and the Americas.

The L type consists of Africans, and especially Sub-Saharan Africans.

The M type consists of:

M1- Ethiopian, Somali and Indian populations. Likely due to much gene flow between the Horn of Africa and the Arabian Peninsula (Saudi Arabia, Yemen, Oman), separated only by a narrow strait between the Red Sea and the Gulf of Aden.

CZ- Many Siberians; branch C- Some Amerindian; branch Z- Many Saami, some Korean, some North Chinese, some Central Asian populations.

D- Some Amerindians, many Siberians and northern East Asians

E- Malay, Borneo, Philippines, Taiwan aborigines, Papua New Guinea

G- Many Northeast Siberians, northern East Asians, and Central Asians

Q- Melanesian, Polynesian, New Guinean populations

The N type consists of:

A- Found in some Amerindians, Japanese, and Koreans

I- 10% frequency in Northern, Eastern Europe

S- Some Australian aborigines

W- Some Eastern Europeans, South Asians, and southern East Asians

X- Some Amerindians, Southern Siberians, Southwest Asians, and Southern Europeans

Y- Ainus and Nivkhs; 1% in Southern Siberia

R- Large group found within the N type.Populations contained therein can be divided geographically into West Eurasia and East Eurasia. Almost all European populations and a large number of Middle-Eastern population today are contained within this branch. A smaller percentage is contained in other N type groups (See above). Below are subclades of R:

B- Some Chinese, Tibetans, Mongolians, Central Asians, Koreans, Amerindians, South Siberians, Japanese, Austronesians

F- Mainly found in southeastern Asia, especially Vietnammarker; 8.3% in Hvar Island in Croatia.

R0- Found in Arabia and among Ethiopians and Somalis; branch HV (branch H; branch V)- Europe, Western Asia, North Africa;

Pre-JT- Arose in the Levant (modern Lebanon area), found in 25% frequency in Bedouin poupulations; branch JT (branch J; branch T)- North, Eastern Europe, Indus, Mediterranean

U- High frequency in Scandinavia, Baltic countries, Mediterranean

Overlap between y-haplogroups and mt-haplogroups

The ranges of specific y-haplogroups and specific mt-haplogroups overlap, indicatingpopulations that have a specific combination of a y-haplogroup and an mt-haplogroup.Y mutations and mt mutations do not necessarily occur at a similar time, anddifferential rates of sexual selection between the two genders combined with founder effect and genetic drift can alter the haplogroup composition of a population, so the overlaps are only rough.

The very rough overlaps between Y-DNA haplogroups and mtDNA haplogroups are as follows:

Y-DNA haplogroup(s) mtDNA haplogroup(s) Geographical area and/or peoples
A L0 South Africa, Khoisan
B L1, L2 Pygmies and related people
E1, E2, E1b1a L3 Sub-Saharan Africa, especially the Bantus
O, N, C3 CZ/C/Z, D, G (M types); A (N type); B, F (R types) East Asia, Siberia
K, M (M9-positive, M45-negative) R, P (R types); Q (M type) as well as various Oceanian-specific M subclades Oceania
R, I, E1b1b, J HV/H/V, JT/J/T, U/K (R types) Europe, West Asia, North Africa, Horn of Africa
Q, C3 A, X, Y (N types); C, D (M types) Easternmost Siberia, the Americas


See also



References

  1. The International Society of Genetic Genealogy see Haplogroup definition in DNA-NEWBIE GLOSSARY [1]
  2. Y Chromosome Consortium
  3. http://www.familytreedna.com/pdf/DNA.RootsiHaplogroupISpread.pdf
  4. Loogvali et al., 2004


External links

General



News



all DNA haplogroups

  • http://www.scs.uiuc.edu/~mcdonald/WorldHaplogroupsMaps.pdf


Y chromosome DNA haplogroups



Mitochondrial DNA haplogroups




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