In the study of the ancient ancestry of humans, scientists focus on "haplogroups", the classification of all humans into ancient family clans based on the unique pattern of genetic markers called "SNPs" found their DNA. SNPs are small changes in the DNA which occur naturally over time. Once a SNP occurs, it becomes a unique lineage marker that is passed down to all future generations. Humans who have descended from the same ancient family clan will share the same pattern of SNPs.
Using SNPs, scientists have been able to plot the haplogroups of all humans living today into a single phylogenetic tree of mankind which shows how all humans are connected to each other in a complex worldwide tree that stems from Africa over 150,000 years ago.
Dozens of haplogroups have been discovered to date, each haplogroup representing a major branch in the phylogenetic tree of mankind.
Each haplogroup can be further refined into "subclades" (finer sub-branches of the tree). As new SNPs are discovered, the phylogenetic tree becomes increasingly detailed with finer branches and enhanced resolution. By testing individuals from around the world and analyzing their precise placement in the phylogenetic tree of mankind, scientists are attempting to piece together the intricate puzzle of ancient human connections and migrations.
How are haplogroups classified?
Haplogroups are named using capital letters of the alphabet (i.e. A, B, C..., etc.). Each haplogroup can be further subclassified into subclades. Subclades are named using numbers and lower case letters following the initial haplogroup letter (i.e. R1b1b2a2b1a is a subclade of haplogroup R).
2 types of DNA hold clues to our ancestral past
In human population genetics, the two types of haplogroups studied are Y-DNA and mtDNA haplogroups:
1. Y-DNA haplogroups (paternal ancestry)
Y-DNA is inherited solely along the paternal line (father to son). The lineage traced is the father's, father's, father's... paternal line. Learn more »
2. mtDNA haplogroups (maternal ancestry)
mtDNA is inherited solely along the matrilineal line (mother to child). The lineage traced is the mother's, mother's, mother's... maternal line. Learn more »
The DNA Ancestry Project allows people to test their DNA in order to predict or confirm which Y-DNA and mtDNA haplogroup they belong and to gain insight into their ancient ancestral origins.
The Y-DNA haplogroup can be predicted us Y-DNA STR testing, but the only way to confirm the Y-DNA haplogroup is through Y-DNA Backbone SNP testing. The mtDNA haplogroup can be predicted by testing the HVR-1 and HVR-2 regions. The mtDNA haplogroup and subclade is confirmed by testing the Coding Region in addition to HVR-1 and HVR-2.
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omparing maps of autosomal DNA with Y-DNA haplogroups
It is tempting to make analogies between the distribution of autosomal admixtures and that of Y-DNA haplogroups. While both of them represent the migrations of certain populations and may roughly correspond to the same source populations, it is essential to understand that any correspondance has its limits for a number of reasons.
Whereas Y-chromosomal lineages can be organised in a neat genealogical tree ('phylogenetic tree' is the technical word), it is much harder for autosomes due to the fact that they get mixed up ('recombined') at every generation with other autosomes. To trace back the origins of a population, the idea is to check which modern populations share the same unique mutations spread out on all 22 pairs of non-sex chromosomes. That's why they are referred to as "admixtures". The names for each admixture are arbitrary and do not necessarily refer to the source population who spread those genes, but usually the geographic region where it is most common today. For example, the Southwest Asian admixture got its name because this set of mutations is most common in the Arabian peninsula nowadays. But Arabic people descend from nomadic herders who lived around the Zagros and Taurus mountains, around northern Mesopotamia, during the Neolithic period. This is also the case of Y-haplogroup J1, with which the Southwest Asian admixture best correlates. In other words, the so-called Southwest Asian admixture found in a European individual may never have come from Southwest Asia (Arabic peninsula) at all, but rather from Anatolia.
Any admixture can be broken down into a number of more specific admixtures, splitting populations that may otherwise have looked closely related. The Northwest European admixture almost certainly comprises DNA markers from two completely different source populations. That is why it is found at high frequencies among the Finns, the Irish and the Iberians, three populations that do not share a lot in common history or phenotypes. It is also found at lower but still substantial frequencies in the Chuvash people (22%) from the Volga region, and the Adygey people (16%) from the North Caucasus, and the Uyghur people (10%) from Northwest China. In all likelihood, the Northwest European component is composed of markers belonging to the Paleolithic population of northern and western Europe (haplogroup I), as well as an Indo-European element (haplogroup R1b) that originated in the Black Sea region.
The way Y chromosomes and autosomes are transmitted is very different. Y chromosomes are strictly inherited from fathers to sons and never recombine, while autosomes are inherited at 50% through each parent. This will inevitably affect their respective geographic distribution since it is known that in most European societies through the ages male children (usually the eldest sons) were the ones who inherited the land, house, farm or even castle from their parents, and therefore stayed from generation to generation at the same place. Women, on the contrary, were married off to men from neighbouring tribes, villages or towns. They were sometimes sent quite far away, especially in royal and noble families that frequently used daughters to seal alliances with other families, or just sought a suitor of a similar social level which they could not find close to home (or at least not without risking inbreeding). This is still common practice among the high aristocracy nowadays. This explains why maternal lineages (mtDNA) and autosomal DNA is much more evenly spread out geographically than paternal lineages (Y-DNA).
Y chromosomes sometimes disappear for evolutionary reasons. Mutations in one lineage can have a negative incidence on male fertility, causing men to have more female offspring (who do not pass on Y-DNA), have less children (contraction of the Y-DNA lineage), or in extreme cases even become sterile (extinction of the Y-DNA lineage).
Y chromosomes may suffer dramatic decline in frequency due to wars, in the event men from a tribe or ethnic group are killed in large numbers by their opponents, and their women taken by the winners. Since autosomes are also passed on by women, autosomes would survive such a scenario even if all male lineages went extinct (which was probably very rare, but once in history is enough to affect a region permanently).
East European admixture
Distribution of the East European admixture in Europe, the Middle East and North Africa
Northwest European admixture
Distribution of the Northwest European admixture in Europe, the Middle East and North Africa
Distribution of the Mediterranean admixture in Europe, the Middle East and North Africa
West Asian admixture
Distribution of the West Asian admixture in Europe, the Middle East and North Africa
Southwest Asian admixture
Distribution of the Southwest Asian admixture in Europe, the Middle East and North Africa
Distribution of the African admixture in Europe, the Middle East and North Africa