Genetic Ancestry Inference
Sampling, Analysis, Interpretation, & Uses
GENETIC ANCESTRY ANALYSES
In our project, we are conducting three kinds of analyses: maternal, paternal, and biparental genetic ancestry.
We will trace your maternal ancestry by analyzing DNA from your cells' mitochondria (small cellular components) and, if you are male, your paternal ancestry from your Y-chromosome. We will also provide ancestry information from both sides of your family ("biparental") by analyzing chromosomal DNA from the cell nucleus, not including the sex chromosomes.
Your cells contain mitochondria, specialized cell subunits that provide most of the cell's energy needs. Mitochondria contain their own DNA (mtDNA) that is transmitted from mother to children of both sexes. We will scan your mtDNA for informative markers that define a genetic lineage that informs individuals about their maternal ancestry. Depending on the lineage, a mtDNA lineage could reflect an antiquity of 1,000 to 100,000 years.
A large portion of the male Y-chromosome is transmitted from father to sons with few to no changes. We will scan your Y-chromosome for informative DNA markers that define a genetic lineage that can inform individuals about paternal ancestry. Depending on the linage, a paternal Y lineage could reflect an antiquity of 1,000 to 100,000 years.
Whereas the maternal and paternal analyses each provide lineage information about no more then two branches of your family tree, a biparental analysis (a.k.a. "autosomal" or "genomic ancestry" analysis) provides biogeographic ancestry estimates for ancestors from all branches of your family tree. Depending on your specific results, the estimates could reflect an antiquity of up to 10,000 years.
MATERNAL ANCESTRY
PATERNAL ANCESTRY
BIPARENTAL ANCESTRY
ANCESTRY INFERENCE: BASIS
Genetic ancestry inference is just that - inference - and therefore not definitive. Genetic ancestry inference relies on individual samples from around the world. These individual samples are compiled into reference databases, which can vary from one testing laboratory to another.
The better the laboratory's reference database, the more potentially accurate the inference estimate. A reference database should consist of individuals with geneaological relationships to ancestral populations from the same area. Because reference databases are often incomplete or lacking in individual samples from particular geographical areas, the usefulness of a reference database for biogeographic estimation can vary both by global locale and on the laboratory conducting the genetic ancestry inference analysis.
This is a recently-taken screenshot from the AncestryDNA.com website. AncestryDNA is a large genetic ancestry testing company in the United States that uses many of the same individual samples used by other companies and academic researchers to compile their reference database.
This map demonstrates that currently, several areas of the world are more densely sampled than others. Poorly sampled global regions will yield low resolution biogeographic estimates, whereas better sampled regions have the potential to provide greater biogeographic resolution.
For example, if an individual's genome shows strong affinities with individual samples from the American continent, the biogeographic ancestry estimate will simply figure as "Americas" for that person. If instead, her genome shows affinities with individual samples scattered throughout Europe, it might be possible to further refine her biogeographic estimate to particular subregions, such as "northern Europe" or "Iberian peninsula."
Because genetic ancestry inference heavily depends on reference databases, a genetic ancestry estimate could differ depending on the reference database. A genetic ancestry inference is also likely to change along with additions to the reference database in the coming years. However, given that major global regions are currently represented in global datasets, it is unlikely that individuals would experience large-scale changes, such as a change in estimate from"Europe" to "Oceania." Finer-scale refinements are more likely, such as from "East Asia/Americas" to simply "Americas" or even "South America."
HOW SHOULD GENETIC ANCESTRY TESTS BE USED ?
Genetic ancestry tests can be used in myriad ways, for example to infer your own ancestry/ies as well as familial relationships between you and others. Researchers will also often use genetic ancestry tests to better understand affiliations among populations.
Ancestry estimates should be considered as preliminary or supplementary tools rather than as conclusive outcomes. As detailed above, ancestry estimates carry a certain degree of uncertainty, and absence of evidence should not constitute evidence of absence. For example, if via your family oral history, you have knowledge of ancestors from a particular geographical area, but a genetic ancestry inference analysis does not confirm it, a simple reason for this may be the use of an inadequate reference database in the analysis.
For this reason, genetic ancestry tests should not be used as the basis for establishing your individual (or group) ancestry affiliation to obtain particular social benefits or entitlements, for example in terms of employment or university admittance.