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HOW
GEOGENE DOES THE ANALYSIS
This
explanation is for analysis of paternal ancestry (GeoFather™).
The analysis of maternal ancestry (GeoMother™) is similar,
with the exception that mitochondrial DNA is examined rather
than the Y chromosome.
In order to unravel the historical roots of your DNA, GeoGene
first needs a sample of your DNA. To do this, we provide you
with a sample kit containing a mouth swab that allows you
to collect loose cells from the inside of your mouth and transfer
these to a special card, which you can then return to us in
the envelope provided
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To
preserve anonymity, each mouth swab sent to the testing laboratory
is identified by a unique serial number rather than the person’s
name.
In the testing lab at the University
of London we extract your DNA from this card. This involves
breaking up the cells to release tiny quantities of DNA. We
separate this DNA from the rest of the cell contents, then
wash it several times to ensure it contains no contaminants
(such as proteins, carbohydrates or lipids) which might hinder
further work. Once DNA has been isolated it is kept in tubes
at -20°C.
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GeoGene’s
goal is to sequence a specific section of your DNA to determine
what base you have at a particular position. Your genome (your
complete set of genes) is extremely large: 3 billion bases
grouped onto 46 chromosomes. We could sequence directly from
the raw DNA but to make the process much more efficient we
amplify the small region (200-400 bases) whose sequence we
wish to obtain employing a technique known as ‘polymerase
chain reaction’ (PCR). PCR is at the core of much molecular
biological work and its inventor, Dr. Cary Mullis, received
the Nobel Prize in recognition of this. PCR allows a scientist
to ‘zoom in’ on a short, specific stretch of DNA
and then make many copies of this region.
GeoGene takes a small quantity of your DNA and adds it to
a tube containing reagents for a PCR reaction. These include
small pieces of DNA called primers, and copies of the nucleotide
sequences located each side of the site we are interested
in, together with individual nucleotides (A, T, C and G) plus
an enzyme known as taq polymerase. This mix is then loaded
onto a machine where it is alternately heated and cooled 20-40
times, helping the reaction to take place and allowing multiple
copies of the relevant sequence to be completed. Once the
process has been completed, the tube will contain millions
of copies of the stretch of DNA we are interested in.
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The
next step in the process is to determine the sequence of this
amplified region. GeoGene does this using a technique known
as automated fluorescent DNA sequencing, which uses differently
coloured dyes for each of the four DNA bases, within the Sanger
chain termination sequencing method. (The Sanger sequencing
method was developed by another Nobel Prize winner, Fred Sanger,
and is the standard today.)
GeoGene analyses your DNA sequence using computer software
to identify the exact base positions that hold the key to
your Y chromosome’s demographic history. By deducing
what sites you are either ‘derived’ or ‘ancestral’
for, we can identify how you fit into the phylogenetic tree
of worldwide Homo sapiens Y chromosomes.
Both the GeoFather™ and GeoMother™ services take
between 4 and 8 weeks to complete. The longer time period
may be necessary if tests need to be rerun. We will inform
you if there is any delay.
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