GENEALOGY-DNA-L ArchivesArchiver > GENEALOGY-DNA > 2004-07 > 1090412160
From: "DNA Heritage" <>
Subject: Re: [DNA] Dodson Group Issue
Date: Wed, 21 Jul 2004 13:16:00 +0100
It's necessary to add to and backup the comments made regarding the
issues around the information possible from the genetic tests that we as
genetic genealogy companies carry out.
A little intro into the Y-chromosome is first needed. As chromosomes
go, it is a lowly one. It has only 60 million bases which as
chromosomes go, is tiny. It also doesn't do a whole lot. 98% of it is
called 'junk DNA' with no known function. The rest of it does contain a
few 'genes' although it would appear that the Y-chromosome's principal
job is to act as a 'male switch', which starts a series of processes
that turns babies into males.
Genes, sections of DNA that help to produce proteins, contains a
sequence of letters a bit like a code-book. The gene that acts as the
male switch in primates is called SRY. This is a different gene to most
other mammals and in fact some mammals have dispensed with the
Y-chromosome altogether and have found other ways for throwing male
Other genes along the Y-chromosome are mainly to do with male fertility.
You'll note that females get along perfectly well without a copy and
have done for quite some time now.
The primary test for genetic genealogy is called an STR (Short Tandem
Repeat) test. We look at small sections of the junk DNA. This junk DNA
is genetic filler and the sections we look for are special repeating
structures, where the code is repeated several times.
It is this number of repeats that you will see in a result. For
example, the marker DYS393 = 13 will have the sequence
This repeat section doesn't encode for proteins and thus isn't medically
informative (it is proteins that help our body to function correctly).
Very rarely, complete sections of the Y-chromosome will be deleted
leading to infertility problems which may include one of the markers we
analyse and thus a marker may not be detected at all, but it should be
stressed that this is very rare and will be apparent to most individuals
affected prior to testing.
An mtDNA test and looks at the DNA within our mitochondria. Cells
within our body are crammed with mitochondria - anywhere between 1,000
and 10,000 per cell - if you look at the cell under a microscope they
are quite evident as small grain-like structures. In Greek, chondros
These mitochondria are very useful and provide energy to the cell. In
fact, they weren't always present. It's thought that a billion or so
years ago a bacterium was engulfed by another cell. Usually this would
have resulted in cell-death, but it appears as though the new merger was
symbiotic - one type of cell provides the energy, the other one provides
protection from the outside - a win-win situation. Over the aeons, the
relationship is much stronger and they have shared functions.
One of the interesting things about mitochondria is that they originate
from other mitochondria, which is different from other organelles
(except for chloroplasts in plants). They also have circular DNA which
is very small, about 16,500 bases long. But within this small piece of
DNA is a bunch of genes which are very important for our bodies.
Because the mitochondria provides the energy to cells, if there is a
problem with the mitochondria the cell doesn't get enough energy and
this is usually evident in the person.
However, and this is very important, there is a large section along the
mtDNA strand called the 'non-coding region'. Again, this region does
not contain genes or encode for proteins. Thus we can safely look at
this section without looking into the medical information that the rest
of the mtDNA may hold.
The comment made by Prof. Dodson "To get maximum use of the
genealogically important information in a DNA analysis, the markers
would need to be essentially the same as those used in genetic
diagnosis." is thus incorrect.
As far as privacy goes, the test lab will only see a sample code and
which test is requested. No name is given. It is only the customer and
DNA Heritage that can match a name up with a sample, although if you are
part of a Surname Project the Project Admin will also be able to do
this. We are registered under and comply with the UK Data Protection
Act which is usually stricter than US or Canadian guidelines in most
areas and about on a par with guidelines in use in other EU countries.
We can't and won't pass your details to another organisation. Samples
are destroyed after 6 months.
Different companies offer longer storage options and thus have protocols
to cover this.
However, because people are aware that the data from the tests aren't
medically informative and cannot identify them as an individual, readily
bank their data within public databases such as Ybase (at
Breaking down misconceptions is a battle but it is slowly being won. To
many, this is the first time that they have been asked for a DNA sample
and for most the first time since high-school that they've had to
understand what DNA is. Genetic tests will become more common in
doctor's surgeries in years to come and thus it is essential to provide
clear and accurate information so as not to skew the public perception
of the utility of such tests. Tests for the 'Jewish gene', Viking DNA,
British tribal association and descendants of Genghis Khan as quoted in
the press grab the reader, but often only have a loose basis in current
science and these again are only helping to maintain misconceptions of
the possibilities and limitations of DNA testing.
It is hard for lay people to dissect the hype from the reality of what
genetic genealogy tests are for and can do. It is only by providing
consistent and clear advice will an understanding by the public be
gained and these barriers of misconception be taken away.