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Y-DNA Matching Process

This page describes the processes and tools used by the administrator of the Taylor Family Genes DNA project in 2013 to assign project members to genetic families. Other admins may use other tools and methods.

Basic principles

These factors determine the way in which we proceed and imply certain realities of the task. Among these is that we are forced rely more on objective DNA data than documentary genealogy.

Purposes of Matching

The general purpose of the matching process is to answer the question as to whether haplotypes are sufficiently similar to indicate that two or more possessors share a common biological paternal lineage.

Matching may have different purposes and methodologies, depending on whether an individual or a project administrator is doing it. The individual is interested in finding his own family history; the administrator in which of his project members "fit together" into a genetic family

Both share an interest in determining whether two or more persons share a common ancestor. Given the long time view of DNA though, a project's time frame may be longer than an individual genealogist's time frame.

Individual Purposes

Project Purposes

First Step -- Criteria

The first step in matching begins without a single result from the laboratory. To apply the scientific method, we must define the criteria for deciding a match exists before obtaining the data for comparison. To get the data, then define criteria, invites subjectivity and bias.

The overall criterion for declaring a genealogically significant match within Taylor Family Genes is this:

Y-DNA indicates a high probability of sharing a common male ancestor who lived since 1350 AD.

This plain-English statement relates the DNA evidence to genealogy and is then translated into quantitative criteria, based on the number of markers compared and the number which agree (or the genetic distance):

  • High probability means equal to or greater than 80%.
  • It has been approximately 660 years since 1350. At an average generation length of 27.5 years, this is about 24 generations.
  • 1350 AD represents the usual earliest beginning of the Genealogic Time Frame in England, a time period for which it is possible to identify ancestors by name, date, place and other characteristics. For specific families, the genealogic time frame may extend further into the past. For others, it may be more recent.
  • In terms of quantification, the take-away from the above is that matches >= 80% CMA at <= 24 generations are considered to be genealogically significant. They indicate the existence of a common paternal ancestor within a time when it is theoretically possible to identify him by name, dates, places and other characteristics.

    Other projects and individuals may, and should, adopt criteria appropriate to their needs.

    Methods

    We use a variety of methods to find matches qualifying for inclusion in a genetic family. What they all have in common is that they assess the similarity of a pair of haplotypes, some better than others.

    1. FTDNA match & results notices

      Family Tree DNA sends, if project admins sign up, notices when its computers find close matches between a member and another person in the database. We've found these to be generally reliable at 37 or more markers; reliable enough to be worth investigating further. Typical notice:
      A Y-DNA37 match has been found between kit ######, {forenames} {surname}, a member of your Family Tree DNA 'Taylor' Project and another person(s) in the Family Tree DNA database.
      Typical results notice:
      Y-DNA26-37 results have been uploaded for kit ######, {forenames} {surname}, a member of your Family Tree DNA 'Taylor' Project. If additional tests (of a different type or higher resolution) were ordered, you will be notified separately when those tests are complete.
    2. Members' match search feature

      A project administrator can log in to any member's "My FTDNA" pages and search for matches as if the admin were the member. This provides both a backup in case of a breakdown in notices and a means of obtaining more information than given in the notice.

    3. Y-DNA TiP

      "Close matches" reported by FTDNA are usually significant in a genealogical sense. However, they are not the only genealogically-significant matches to be found. The Y-DNA TiP available to project admins via the GAP permits computation of TiP scores between any two members of a project. TiP, Time Predictor, is a proprietary TMRCA calculator by FTDNA. Its advantage over other TMRCA calculators is use of mutation-rate adjusted individual marker probabilities. Read more about TiP here.

      We use the cumulative probability at 24 generations, comparing 37 or more markers, without adjusting for paper-trail information.

    4. Y-DNA Genetic Distance

      Another GAP tool is handy. It permits comparing each project member to each other on the basis of genetic distance. After selecting one member, the others are ranked in order of genetic distance from  closest to furthest. The TiP tool can then be used to  more precisely assess similarity of haplotypes.
    5. "Eyeballing" results

      Less satisfactory
    6. Spreadsheets

      Data can be downloaded for analysis in a computer spreadsheet, such as Excel.
    7. Other

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    Caveat

    There are such things as "coincidental matches", which tend to occur most often among the more common haplotypes. The patterns of marker/allele values may be similar, but they don't spring from a common source. The similarity is more likely due to "convergent evolution", in which organisms of different ancestral heritage evolve to like forms.

    For example, you might see that you have hundreds of reported close matches at 37 markers. Not only are these too many ofor follow up, you are probably unrelated in genealogic time to most of them.

    In such instances, SNP testing is recommended to eliminate matches of obviously different DNA inheritance. SNP testing in some depth can tell you who you are less related to.