A Brief Introduction to Genealogical DNA

Concerns and Myths about Genealogical DNA

Since other, non-genealogical, DNA is often in the news, there is always some concern about personal safety, legal and professional matters in relation to any DNA testing. There are also some other misunderstanding about genealogical DNA. We’ll just handle these are bullets:

  • Genealogical testing does not require exhuming any body.
  • The DNA sample is not from blood, but by a swab from the mouth (inside the cheek) – simple, quick and painless.
  • The UK has The Human Tissue and Privacy Act and the US the Genetic Information and Non-Discrimination Act which protects people from their DNA information being used against them for insurance or employment reasons.
  • No medical information can be derived from these non-coding portions of the genome.

What is Genealogical DNA?

A portion of the human genome happens to be extremely useful for tracing strictly biological genealogy. The portion of the genome that is used for genealogical testing has no known use other than to fill spaces between genes. Scientists have chosen a number of positions along this portion of the genome for this purpose. First let’s look very briefly at what positions and markers are, then why the genetic researchers have chosen the ones they have.

What are Markers?

The genome can be visualized as a colorful striped shirt which father’s pass to their sons. Each stripe on the shirt is a “marker” and the color of that stripe is the marker’s “value”. Some of these stripes can have only a few different colors, others have many possible colors. There are actually many many stripes on these shirts, but scientists have chosen to use only a few of them because of their particular value for genealogy.

Why These Particular Markers?

The reason these shirts are valuable at all is because, generally speaking, they are passed unchanged to children. However, some of the stripes may change color while being passed down. These changes are called mutations and they just happen randomly – except that some stripes change much more frequently than others. Scientists have chosen several slowly mutating stripes so that they can determine what they call a “haplogroup” for the DNA sample being tested. The stripes or markers that are used to determine haplogroup mutate very infrequently and so tend to be very stable down through many generations. They can thus be used to identify whole populations of descendants and can be used to trace migrations of these haplogroups down through extended history.

Other stripes (markers) change much more frequently and some of these are included in the DNA testing to allowing matching of rather closely related cousins and thus determining how closely related they might be. These markers may mutate every 20 generations or so, and by including several of this type it is likely that one marker or another will change every few generations. It is this combination of many slow and many fast mutating markers that makes genetic genealogy possible and very useful.

Why Does My Sample Match People Who Are Not Related to Me?

Since there are actually many many stripes on these shirts, and it costs almost £3 ($4) to determine the color of just one stripe, it is simply not feasible to test them all. So it is quite possible that the particular markers being tested will match with others because most stripes on these shirts are being ignored. This is why it is important, in most every case, to only match with people who are known to be, or strongly suspected to be rather close relatives. This generally means people with the same surname for the Y-DNA (male lineage) tests.

So If Unrelated People Can Match, What Good Is DNA?

A quick example: The first three samples tested in the Pemberton DNA Project just happened to be from Pemberton lines traceable back to the Virginia Colony. It was supposed that these lines would merge there, but the DNA samples proved that their common ancestor was several generations earlier. Thus the documentary data in Virginia could now be examined in the correct light – this made a very big difference in the interpretation of the documents available.

We Can Determine the Y-DNA Profile of Ancient Pembertons

With only a few Y-DNA samples from close lines, it is possible to determine what the Y-DNA profile would have been for their common ancestor. This profile then becomes a kind of “standard” that can be used to estimate the “genetic distance” or probability of a close relationship. This then becomes valuable help to the researcher who is sorting through the documentary information.

The Autosomal Test Can Find Relatives Quickly

The autosomal test at Family Tree DNA is called the Family Finder test and for good reason.

Debunking the Myths about Genealogical DNA

We’ll just handle these are bullets:

  • Genealogical testing does not require exhuming any body.
  • The DNA sample is not from blood, but by a swab from the mouth (inside the cheek) – simple, quick and painless.
  • The UK has The Human Tissue and Privacy Act and the US the Genetic Information and Non-Discrimination Act which protects people from their DNA information being used against them for insurance or employment reasons.
  • No medical information can be derived from these non-coding portions of the genome.

If you have any concerns about DNA testing that haven’t been covered here, please contact us at DNA@pembertonfamily.com.

More Information About Genealogical DNA

You can find some links to other articles on DNA in the Utilities menu. Select the Research Links submenu.