Many people spend thousands of dollars and hundreds of hours tracking their origins through historical records or verbal accounts. This is an expensive and time consuming method that may or may not be accurate. With the human genome finally sequenced and recent advances is DNA technology using Single Nucleotide Polymorphisms (SNP) a new type of genetic test called BioGeographical Ancestry (BGA) can be generated by analyzing your DNA. In the human populations, there are some individuals of relatively pure BioGeographical Ancestry (BGA), such as sub-Saharan Africans from Nigeria, Europeans from Northern Europe, East Asians from Northern China and Native Americans from isolated regions of Southern Mexico. In other places, such as the United States, there are recently (in evolutionary time) admixed (admixture is the blending of two or more races within individuals) peoples such as African Americans (a blend of African and European BGA) and Hispanics (a blend of Native American and European BGA). Of course there are more than just four continental population groups, and a large fraction of the world population is admixed to a greater or lesser degree. SNP technology can determine your precise ancestral proportions. For example, it might reveal that you are of 80% African and 20% Indo-European, or 95% African and 5% Indo-European ancestry (or some other mix/ratio, as the case may be).
The human DNA code (genome) contains 3.1647 billion chemical nucleotide bases (A, C, T, and G). Approximately, 99.9% of these nucleotide sequences are the same in all people. This leaves about two million nucleotides (0.1%) that are unique from person to person. These sequence differences account, in part, for why we look, think, and behave differently and some of these nucleotide variations (about 2,000 or so) are dramatically different amount the various races. It so happens that by analyzing your DNA sequences using Single Nucleotide Polymorphisms (SNP) technology at some of these latter sites, it is possible to not only infer your major ancestry (which you probably already know) but your ancestral proportions (which, you probably do not know). For example, have you ever wondered whether you are of purely Indo-European origin or a blend of Indo-European and Native American (or other) ancestry? If you are of majority African heritage, have you ever wondered whether you are also of Indo-European descent, or perhaps of East Asian descent? If you know that you are a blend of ancestries, do you know what proportions you are of each? SNP technology has allowed us to precisely determine your ancestral admixture .Single Nucleotide Polymorphisms (SNPs) can be use to determine your Biological ancestry proportion by identifying Ancestry Informative Markers (AIMs) within your DNA. AIMs are located in that 0.1% of the human genome that differ in sequence between the world’s various populations and by identifying AIMs it is possible to make a strong inference of your ancestral mix. The Pennsylvania State University (PSU) has identified the world’s only comprehensive set of AIMs. This patent pending science was published in late 1999, and then again in 2001 and 2002 (See Parra et al.; Pfaff et al.; and Frudakis et al). SNPs enable the determination of individual ancestry proportions (called “admixture ratios?) from DNA. Because it uses genetic markers spread throughout all the chromosomes, with unique and specific anthropological characteristics, it is quite a distinct product from STR, Y-chromosome or mitochondrial DNA testing used in other types of anthropological settings.
If your proportions are of three or fewer ancestries, we would provide you with a graphical “shapshot? of your results called a triangle plot. This plot is provided if your ancestry is derived from three or fewer groups (otherwise, it is impossible to represent your data in 2-dimensional space). The point on this plot is called a Maximum Likelihood Estimate (MLE), and only one is shown on this plot. This MLE represents the best estimate of your ancestral proportions. To read a triangle plot, you drop a perpendicular line from the vertex (triangle point) of each triangle to the triangle edge below it. In this example, a line from the Native American vertex to the line below serves as a scale for the percentage of Native American ancestry – from 0% at the base to 100% at the vertex (or tip). This individual is about 15% Native American. A line for each of the other two vertices is created. In addition to being able to see that the person is of 15% Native American ancestry, you can see that the person is of 60% European Ancestry and 25% African ancestry as well. You will notice that the three percentages must add up to 100%. African American: In this example, individuals who described themselves as African American were plotted (NAM-Native American, EUR–Indo-European and AFR– African). It can be seen that relatively few of these individuals are of pure African descent (those whose point estimates reside relatively close to the AFR vertex). Many have significant EUR or NAM admixture (their point estimate resides away from the AFR vertex towards one or both of these). In fact some are more Indo-European origin than African (their point estimates reside further towards the EUR vertex than the AFR vertex). It is well known that the history of African Americans has been marked not only by the forced migration from Africa, but also by the admixture with the other ethnic groups they met when they arrived in North America, namely Europeans and Native Americans. However, few historical records address the issue of admixture. Additionally, there have been important factors that, in the time since the abolition of slavery until the present, have configured the present African-American population. Of special interest is the pattern of migration of African Americans within the US over the past 150 years. In this sense, the redistribution of African Americans in the Southern States during the 19th century, and the Great Migration from the rural South to the urban areas in the North beginning after World War I are of particular relevance, and have had an enormous impact in defining the present distribution of the African-American population in the US (Johnson and Campbell, 1981). The results thus appears to capture the differing levels of NAM and EUR admixture present in African American individuals. Caucasain: In this example individuals who describe themselves as “Caucasian? were plotted. You see that most are of these individuals plot in the EUR region of the triangle, but some of the individuals exhibit significant NAM or AFRancestry. Hispanic or Mexican American: Individuals that described themselves as Hispanic or Mexican American.were plotted. Mexican Americans show a high degree of NAM contribution, which agrees with what is known from the anthropological history. For example, it is known that soon after the Spanish conquest of Mexico, at the beginning of the 16th century, intermixture of the Spanish men with Amer-indian women resulted in an increasingly important mixed population (Mestizos) and this racial mixing continued through the three centuries of Spanish domination in “New Spain?, configuring both biologically and culturally the Mexican population. Thus, the distribution of ANCESTRY point estimates along the NAM – EUR axis is consistent with what is known about the anthropological history of this group. These are relatively simple examples, using only a 3-dimensional plot with 3 ancestral groups. References:
Parra, E. et al. 1998. Estimating African American Admixture Proportions by Use of Population Specific Alleles. Am. J. Hum. Genet. 63:1839-1851.
Pfaff, C. et al. 2001. Population Structure in Admixed Populations: Effect of Admixture Dynamics on the Pattern of Linkage Disequilibrium. Am. J. Hum. Genet. 68:198-207.
Parra, E. et al. 2001. Ancestral Proportions and Admixture Dynamics in Geographically Defined African Americans Living in South Carolina. American Journal of Physical Anthropology 114:18-29.
N Patil et al. 2001. Blocks of limited haplotype diversity revealed by high-resolution scanning of human chromosome 21 Science 294:1719-1723.