Autosomal chromosomes DNA, the Family Finder test

The Family Finder test (FF) is capable of finding relatedness between two individuals regarding all their ancestral lines. It is based upon autosomal DNA which is inherited from all lines. Cousins can easily find themselves regardless of their gender and even when five generations separate them. The underlying technology is to identify blocks of DNA part of the 22 pairs of autosomal chromosomes which form long segments shared in common by the two tested persons. Using this approach, the team of bioinformaticians at FTDNA has developed algorithms able to estimate the degree of relationship between two persons.

Opportunities to find other related persons are multiple:
  1. Aunts and Uncles, Parents and Grandparents, half-siblings,
  2. Cousins, up to the fourth degree and possibly beyond.

After being subjected to a Family Finder test at FTDNA, your results will be compared to those of others contained in the Family Finder database. You will thus be able to:

  1. Sort your matches by degree of kinship with you;
  2. See their names and E-mail addresses and therefore be in a position to get in touch with them;
  3. Download your raw data for later use or to subject them to data-analysis softwares developed by independent third parties;

The following figure illustrates the kind results you would get in a match with a brother or a sister. Orange segments correspond to shared long segments.


The number of shared segments decreases rapidly with the diminishing of degree of relatedness between two persons. By contrast, some common segments may subsist after several generations, indicating that the compared persons share couples of ancestors, as here between two cousins of the fourth degree:


When their genealogical trees are compared, a common shared couple is found between the two tested persons, which could account for this segment of 14.88 centimorgans on chromosome 12.

Such an approach can help break impasses in documentary research and can be extremely useful for adopted persons to find relatives, and with some chance after other tests, to know who their biological parents were.

For more information on this test consult the FTDNA pages on the subject(external link)
or the ISOGG wiki(external link) on FF.

There is a similar test sold by 23andMe. However, at the French Heritage DNA project we are not in a position to handle their results for the moment.

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