biologists have reached a similar conclusion based on analysis of Amerindian language groups and ABO blood group system distributions.[14][15][16] Contents [hide] 1 Background2 Y-DNA2.1 Haplogroup Q2.2 Haplogroup R12.3 Haplogroup C-P393 mtDNA4 AtDNA5 Overlaps between DNA types6 Old world genetic admixture7 Blood groups8 Genealogical testing9 See also10 References11 Further reading12 External links Background[edit]Further information: Timeline of human evolution and Recent African origin of modern humansA single-nucleotide polymorphism (SNP) is a change to a single nucleotide in a DNA sequence.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.[17] The Y chromosome spans about 60 million base pairs (the building blocks ofDNA) and represents about 2 percent of the total DNA in all human cells.[18] 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 newsubclade (single-nucleotide polymorphism (SNP)).[19]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.[20][21]Both females and males inherit their Mitochondrial DNA (mtDNA) only from their mother.[22] This line of biological inheritance, therefore, stops with each male.[23] Consequently, Y-DNA is more commonly used by the general public for tracing genetic heritage of a direct male line.[23][24][25]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.[2] 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 differentnucleotide.[2] 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.[26]Y-DNA[edit]For more details on individual Amerindian groups by Y-DNA, see Y-DNA haplogroups in Indigenous peoples of the Americas.The Y chromosome consortium has established a system of defining Y-DNA haplogroups by letters A through to T, with further subdivisions using numbers and lower case letters.[27]Haplogroup Q[edit]For more details on this topic, see Haplogroup Q-M242 (Y-DNA).Spread of Haplogroup Q in Indigenous populations.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[28][29] In Eurasia haplogroup Q is found among indigenousSiberian 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.[30] The Ket are thought to be the only survivors of ancient wanderers living in Siberia.[5]