The Y chromosome is passed down directly from father to son; all male humans (Y chromosomes) today trace back to a single prehistoric father termed "Y chromosomal Adam" originating in Africa. The Y chromosome spans about 60 million base pairs (the building blocks of DNA) and represents about 2 percent of the total DNA in all human cells. The original "Y chromosomal Adam"-DNA sequencing has mutated rarely over the 20,000 generations, but each time a new mutation occurs, there is a new branch in a haplogroup, resulting in a new subclade (single-nucleotide polymorphism (SNP)).
MtDNA mutations are also passed down relatively unchanged from generation to generation, so all humans share the same mtDNA-types. The logical extension of this is that all humans ultimately trace back to one woman, who is commonly referred to as Mitochondrial Eve. Both females and males inherit their Mitochondrial DNA (mtDNA) only from their mother. This line of biological inheritance, therefore, stops with each male. Consequently, Y-DNA is more commonly used by the general public for tracing genetic heritage of a direct male line.
An autosome (atDNA) is a chromosome that is not a sex chromosome – that is to say, there are an equal number of copies of the chromosome in males and females. Autosomal DNA testing is generally used to determine the "genetic percentages" of a person's ancestry from particular continents/regions or to identify the countries and "tribes" of origin on an overall basis. Genetic admixture tests arrive at these percentages by examining (SNP), which are locations on the DNA where one nucleotide has "mutated" or "switched" to a different nucleotide. One way to examine the support for particular colonization routes within the American landmass is to determine if a closer relationship between zygosity and geography is observed when “effective” geographic distances are computed along these routes, rather than along shortest-distance paths.
Q-M242 (mutational name) is the defining (SNP) of Haplogroup Q (Y-DNA) (phylogenetic name). Within the Q clade, there are 14 haplogroups marked by 17 SNPs.2009 In Eurasia haplogroup Q is found among indigenous Siberian populations, such as the modern Chukchi and Koryak peoples. In particular, two groups exhibit large concentrations of the Q-M242 mutation, the Ket (93.8%) and the Selkup (66.4%) peoples. The Ket are thought to be the only survivors of ancient wanderers living in Siberia. Their population size is very small; there are fewer than 1,500 Ket in Russia.2002 The Selkup have a slightly larger population size than the Ket, with approximately 4,250 individuals.
Haplogroup Q-M3 (Y-DNA) is defined by the presence of the rs3894 (M3) (SNP). The Q-M3 mutation is roughly 15,000 years old as that is when the initial migration of Paleo-Indians into the Americas occurred. Q-M3 is the predominant haplotype in the Americas, at a rate of 83% in South American populations, 50% in the Na-Dené populations, and in North American Eskimo-Aleut populations at about 46%. With minimal back-migration of Q-M3 in Eurasia, the mutation likely evolved in east-Beringia, or more specifically the Seward Peninsula or western Alaskan interior. The Beringia land mass began submerging, cutting off land routes.
Since the discovery of Q-M3, several subclades of M3-bearing populations have been discovered. An example is in South America, where some populations have a high prevalence of (SNP) M19 which defines subclade Q-M19. M19 has been detected in (59%) of Amazonian Ticuna men and in (10%) of Wayuu men. Subclade M19 appears to be unique to South American Indigenous peoples, arising 5,000 to 10,000 years ago. This suggests that population isolation and perhaps even the establishment of tribal groups began soon after migration into the South American areas. Other American subclades include Q-L54, Q-Z780, Q-MEH2, Q-SA01, and Q-M346 lineages. In Canada, two other lineages have been found. These are Q-P89.1 and Q-NWT01.
Haplogroup R1 (Y-DNA) (specially R1b) is the second most predominant Y haplotype found among indigenous Amerindians after Q (Y-DNA). The distribution of R1 is believed to be associated with the re-settlement of Eurasia following the last glacial maximum. One theory put forth is that it entered the Americas with the initial founding population. A second theory is that it was introduced during European colonization. R1 is very common throughout all of Eurasia except East Asia and Southeast Asia. R1 (M137) is found predominantly in North American groups like the Ojibwe (79%), Chipewyan (62%), Seminole (50%), Cherokee (47%), Dogrib (40%) and Papago (38%).
Spread of Haplogroup C-M217 in Indigenous populations.
Haplogroup C-M217 is mainly found in indigenous Siberians, Mongolians and Oceanic populations. Haplogroup C-M217 is the most widespread and frequently occurring branch of the greater (Y-DNA) haplogroup C-M130. Haplogroup C-M217 descendant C-P39 is commonly found in today's Na-Dené speakers, with the highest frequency found among the Athabaskans at 42%. This distinct and isolated branch C-P39 includes almost all the Haplogroup C-M217 Y-chromosomes found among all indigenous peoples of the Americas. The Na-Dené groups are also unusual among indigenous peoples of the Americas in having a relatively high frequency of Q-M242 (25%).
Schematic illustration of maternal (mtDNA) gene-flow in and out of Beringia, from 25,000 years ago to present.
When studying human mitochondrial DNA (mtDNA) haplogroups, the results indicate that Indigenous Amerindian haplogroups, including haplogroup X, are part of a single founding east Asian population. It also indicates that the distribution of mtDNA haplogroups and the levels of sequence divergence among linguistically similar groups were the result of multiple preceding migrations from Bering Straits populations. All Indigenous Amerindian mtDNA can be traced back to five haplogroups, A, B, C, D and X. More specifically, indigenous Amerindian mtDNA belongs to sub-haplogroups that are unique to the Americas and not found in Asia or Europe: A2, B2, C1, D1, and X2a (with minor groups C4c, D2, D3, and D4h3). This suggests that 95% of Indigenous Amerindian mtDNA is descended from a minimal genetic founding female population, comprising sub-haplogroups A2, B2, C1b, C1c, C1d, and D1. The remaining 5% is composed of the X2a, D2, D3, C4, and D4h3 sub-haplogroups.
X is one of the five mtDNA haplogroups found in Indigenous Amerindian peoples. Unlike the four main American mtDNA haplogroups (A, B, C and D), X is not at all strongly associated with east Asia. Haplogroup X genetic sequences diverged about 20,000 to 30,000 years ago to give two sub-groups, X1 and X2. X2's subclade X2a occurs only at a frequency of about 3% for the total current indigenous population of the Americas. However, X2a is a major mtDNA subclade in North America; among the Algonquian peoples, it comprises up to 25% of mtDNA types. It is also present in lower percentages to the west and south of this area — among the Sioux (15%), the Nuu-chah-nulth (11%–13%), the Navajo (7%), and the Yakama (5%). Haplogroup X is more strongly present in the Near East, the Caucasus, and Mediterranean Europe. The predominant theory for sub-haplogroup X2a's appearance in North America is migration along with A, B, C, and D mtDNA groups, from a source in the Altai Mountains of central Asia.
Sequencing of the mitochondrial genome from Paleo-Eskimo remains (3,500 years old) are distinct from modern Amerindians, falling within sub-haplogroup D2a1, a group observed among today's Aleutian Islanders, the Aleut and Siberian Yupik populations. This suggests that the colonizers of the far north and subsequently Greenland originated from later coastal populations. Then a genetic exchange in the northern extremes introduced by the Thule people (proto-Inuit) approximately 800–1,000 years ago began. These final Pre-Columbian migrants introduced haplogroups A2a and A2b to the existing Paleo-Eskimo populations of Canada and Greenland, culminating in the modern Inuit.
Genetic diversity and population structure in the American landmass is also done using autosomal (atDNA) micro-satellite markers genotyped; sampled from North, Central, and South America and analyzed against similar data available from other indigenous populations worldwide. The Amerindian populations show a lower genetic diversity than populations from other continental regions. Observed is a decreasing genetic diversity as geographic distance from the Bering Strait occurs as well as a decreasing genetic similarity to Siberian populations from Alaska (the genetic entry point).
Also observed is evidence of a higher level of diversity and lower level of population structure in western South America compared to eastern South America. There is a relative lack of differentiation between Mesoamerican and Andean populations, a scenario that implies that coastal routes were easier for migrating peoples (more genetic contributors) to traverse in comparison with inland routes.
The over-all pattern that is emerging suggests that the Americas were recently colonized by a small number of individuals (effective size of about 70), which grew by a factor of 10 over 800 – 1000 years. The data also shows that there have been genetic exchanges between Asia, the Arctic and Greenland since the initial peopling of the Americas.
"Las castas" - Painting containing complete set of 16 casta combinations. An 18th century socio-racial classification system used in the Spanish American colonies.
Interracial marriage and interracial sex and, more generally, the process of racial admixture, has its origins in prehistory. Racial mixing became widespread during European colonialism in the Age of Discovery. Genetic exchange between two populations reduces the genetic distance between the populations and is measurable in DNA patterns. During the Age of Discovery, beginning in the late 1400s, European explorers sailed the oceans, eventually reaching all the major continents. During this time Europeans contacted many populations, some of which had been relatively isolated for millennia. The genetic demographic composition of the Eastern Hemisphere has not changed significantly since the age of discovery. However, genetic demographics in the Western Hemisphere were radically altered by events following the voyages of Christopher Columbus. The European colonization of the Americas brought contact between peoples of Europe, Africa and Asia and the Amerindian populations. As a result, the Americas today have significant and complex multiracial populations. Many individuals who self-identify as one race exhibit genetic evidence of a multiracial ancestry.
Research by Ludwik and Hanka Herschfeld during World War I found that the frequencies of blood groups A,B and O differed greatly from region to region. The "O" blood type (usually resulting from the absence of both A and B alleles) is very common around the world, with a rate of 63% in all human populations. Type "O" is the primary blood type among the indigenous populations of the Americas, in-particular within Central and South America populations, with a frequency of nearly 100%. In indigenous North American populations the frequency of type "A" ranges from 16% to 82%. This suggests again that the initial Amerindians evolved from an isolated population with a minimal number of individuals.
Distribution of ABO blood types in various modern Indigenous Amerindian populations Test results as of 2008
A genealogical DNA test examines the nucleotides at specific locations on a person's DNA for genetic genealogy purposes. The test results are not meant to have any medical value; they are intended only to give genealogical information. Genealogical DNA tests generally involve comparing the results of living individuals to historic populations. The general procedure for taking a genealogical DNA test involves taking a painless cheek-scraping (also known as a buccal swab) at home and mailing the sample to a genetic genealogy laboratory for testing. Genetic testing results showing specific sub-Haplogroups of Q, R1 and C3b implies that the individuals ancestry is, in whole or in-part, indigenous to the Americas. If one's mtDNA belonged to specific sub-Haplogroups of, A, B, C, D or X2a, the implication would be that the individual's ancestry is, in whole or part, indigenous to the Americas.
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