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Testing Modes

Regardless of the form of DNA tested (autosomal, mitochondrial or Y-chromosome), the goals of testing determine whether the testing falls into

  1. "Focused mode", or
  2. "Seek mode"
  3. "Investigative mode"

Focused Mode

Focused testing proceeds from a hypothesis that known individuals share a particular family relationship or relationships. The purpose of the testing is to confirm or refute the hypothesis. This mode was one of the earliest applications of genetic genealogy.

Each party to the relationship provides a DNA sample, which is then analyzed in accordance with the nature of relationship, e.g., Y-, mt or At. The results are compared and evaluated as to confirmation or refutation.

A focused mode example was the use of Y-DNA to investigate the question of whether Thomas Jefferson was the direct paternal ancestor of the descendants of Sally Hemmings.  (The answer was either he or his brother.)

Problems

The chief problem is that the individuals must be identified and must submit a sample for analysis. If this condition cannot be met, the focused mode is infeasible.

It should be noted that DNA testing is much more effective at refuting a hypothesis than confirming one. DNA has a low propensity to "Type 1" errors, incorrect rejection of a true hypothesis. However, it is subject to "Type 2" errors, failure to reject a false hypothesis.

The outcome may be any of these three:

  1. The hypothesis is refuted. The supposed relationship is genetically ruled out;
  2. The hypothesis is probabilistically supported to a pre-determined level of confidence. The hypothesis is more likely true than false;
  3. The data is too ambiguous to either support or refute the hypothesis.

 

Seek Mode

Sometimes called "blind testing", this mode is about finding an unknown individual who may share a family relationship. It has become the dominant mode in genetic genealogy, due to large online databases and algorithms facilitating online searches for close matches.

In this mode, one individual submits a sample and has it analyzed in accord with the nature of relationships, e.g.:

The results are entered into a database and an automated search compares to each set of results already in the database. A computer algorithm identifies and reports each set which meets predetermined criteria, i.e., "matches". Interpretation of the match may then be applied, using probability theory, genetic science, "paper trail" comparison, etc.

Problems

Problems encountered include:

Investigative mode

The purpose of the investigative mode is not to asses or find a particular relationship, but to learn about one's genetic heritage. This mode relates more to the ancient (pre-historic) past than to the genealogical time frame in which specific persons can be identified as ancestors.

For example, one may want to answer any or all of these questions: