Genetic Genealogy

We are now on the threshold of a revolution in the field of biotechnology where the sequencing of our DNA can be performed for a very affordable price. For genealogists, this opens the door to a new world: instead of relying exclusively on available records, it is possible to directly use the genetic inheritance that has been passed down over generations.

There are several genetic testing companies in the market that are dedicated to genealogy applications. Most of them determine only what is known as the "haplogroup". The most common haplogroups are the Y chromosome (Y-DNA) and the mitochondrial (mtDNA). These two haplogroups are transmitted exclusively by the paternal line (Y-DNA) and the maternal line (mtDNA), and allow to trace the evolution and migration of the human species and more specifically of our prehistoric ancestors.

However, once you are willing to do your genetic analysis, it is recommended that you carry out the tests on a company that has a vast database that allows you to compare your DNA with that of other genealogists, and find those who share significant parts with you: your distant relatives. In this way, it combines the useful with the pleasant: besides extending its known family, since this distant cousin is also interested in genealogy, both can enrich the respective trees. One of the companies conducting these tests and having a large user base is the FamilyTreeDNA (FTDNA )1. Other companies with extensive databases include Ancestry, 23andMe, and MyHeritage.

FTDNA offers 3 types of tests:

  • FamilyFinder: an autosomal test that identifies matches within all ancestor lines in the last 5 generations
  • Y-DNA: for men only, allows identification of relatives exclusively on the parental line
  • mtDNA: for both sexes, it allows the identification of relatives exclusively on the maternal line


FamilyFinder DNA transmission

This is by far the recommended test among the three types offered. In this type of test, the autosomal DNA is tested, this is transmitted by both parents with about half of our an individual's DNA coming from each parent. The exact mix differs between each person, even between siblings. However, the following approximations can be made of the percentage of genetic material we receive from our ancestors:


Generation Relationship % genes
1 Parents (2) 50.00%
2 Grandparents (4) 25.00%
3 Great-grandparents (8) 12.50%
4 Great-great-grandparents (16) 6.25%
5 Great-great-great-grandparents (32) 3.12%
6 Great-great-great-great-grandparents (64) 1.56%

Due to the declining percentage of transmitted genes, the identification of ancestors (and their descendants) from the 6th generation onwards becomes more difficult. This is why it is recommended that you start by testing older ancestors with FamilyFinder.

By performing this test, FTDNA will compare your DNA with other genealogists who did the same test, and will present you with matches with those who share a genetic block of considerable size with you. For this test, it is recommended to share your family tree so that your distant relatives can try to identify the common ancestor.


Y-DNA transmission

The Y-DNA test tests the Y chromosome that is part of the XY pair of chromosomes that determines the male sex. For this reason, this test can only be performed by men - women can always test a brother, father or another male on the paternal line. Since the mother's DNA does not participate in the gene pool on this chromosome, the Y is passed exclusively from father to son with very few changes.

FTDNA offers various levels of Y-DNA tests, depending on the number of STR markers (Short Tandem Repeat) tested. The following table shows the generations where the confidence level is 95% for genetic distance according to the number of markers tested:


  Genetic distance
  0 1 2
Y-DNA 12* ≤29 ≤47 -
Y-DNA 25* ≤13 ≤20 ≤27
Y-DNA 37 ≤7 ≤10 ≤14
Y-DNA 67 ≤7 ≤9 ≤14
Y-DNA 111 ≤5 ≤7 ≤9

* Only available as an upgrade.

FTDNA also provides the Big Y700 test, which in addition to providing circa 700 STRs, also identifies the various SNPs (Single nucleotide polymorphism), allowing a more accurate classification within the Y-DNA haplogroups. Depending on the haplogroup, the time to the common ancestor of all individuals with the same terminal SNP may be only a few centuries.


mtDNA transmission

The mtDNA test sequences DNA from the mitochondria that are part of our cells. Unlike the nuclear DNA that results from DNA recombination of both parents, our mitochondrial DNA is passed exclusively by our mother. With this test it is therefore possible to test the maternal line and discover possible relatives with common ancestors in this line of mothers' mothers. Unlike the Y-DNA test, this mtDNA can be done by both women and men.

FTDNA offers two levels of mtDNA test, the mtDNA+ and the mtFull Sequence. mtDNA + tests only the hypervariable regions 1 and 2 (HVR1 and HVR2), while mtFull Sequence tests the complete mitochondrial DNA. Note that the first test has mostly anthropological interest, since there are usually several thousand people with identical HVRs pairs. Only the complete test can be used to positively identify more recent kinship relationships.


In addition to testing, FTDNA also provides support for DNA projects. These projects are managed by teams of volunteer genealogists and serve to group individuals with common interests.

In addition to several surname projects (eg where all 'Silva' are invited to participate), there are also specific haplogroup projects and those of regional interest. In the latter type, the following projects are of particular interest:

Hic Sunt Dracones (Here be dragons)

Finally, a word of advice. For those who are not willing to receive the answer, it may be best to start by not asking the question. In this case, the genes reveal the biological parents genealogy. The parish registers tell the story of the "affective" parents.

The two do not always coincide ... There are estimates that the average NPE (non-paternity events) rate may be around 2%. That is, in every 100 individuals, the biological father of 2 of them does not correspond to the "affective" parent. In genealogical terms, this means that in a complete tree up to the 7th generation, containing 127 individuals, there are on average 2 errors in the attribution of paternity.

Note 1: is an affiliate of FamilyTreeDNA (FTDNA), a US company that sells DNA tests to the world's genealogy community. Links on this site for FTDNA contain an affiliate reference. The only information shared between us and FTDNA is this reference. When you purchase a test on FTDNA after following one of these links, a commission will be generated that helps to support the maintenance and development of this site. The commission does not change the final price of the products.

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