We all have 24 chromosomes. Each chromosome contains numerous genes, some "expressed" i.e. dominant, some not, so-called recessive.
DNA testing as it is now known has nowt to do with genes. What various DNA tests do is to look at the parts of the DNA molecule of the chromosomes outside the genes. In these areas there are, every so often, groups of repeated atoms in the DNA molecule, known as short tandem repeats.
In any one such location or "marker" in the DNA molecule, you might have, say, 7 repeats, but I might only have 4. If a decent number of the STRs are the same, then there's a probability of common ancestry sometime way back.
The basic number of markers for the male Y chromosome test is only 10, but such a low number involves an error in terms of the situation where, say, 7 of 10, match with someone else. This is known as "confidence limits", normally expressed as a percentage, e.g. that 10 marker match might be expressed as 95% confidence limits which means that there is a 5% chance that the match is actually a false positive (it gets even more complicated than that as there as associated errors and therefore confidence limits connected with the analytical techniques involved, but let's not get into that !
)The higher the number of markers tested the more accurate will be the results, and the higher the confidence limits that the answer is correct.
This ain't an easy field in terms of the science involved, and the associated need to have an understanding of some fairly sosphisticated statistical aspects. There's no real "DNA testing for Dummies" that IK know of, but http://blairgenealogy.com/dna/dna101.html comes close.
There is another form of DNA, in all of our cells, apart from blood cells, known as mitochodrial DNA, mtDNA for short. This is inherited from the mother.
In the case of the Y chromosome DNA and mtDNA, mutations take place verytime and generations. The average rates of such mutations are reasonably well known, so that, given any two DNA test results, it's possible to derive a figure for the number of generations since the most recent common ancestor. BTW mtDNA mutates more slowly than Y chromosome DNA.
I can appreciate that to give such an explanation of Gene Detectives may not have been appropriate for a morning TV show, but something should have been attempted, with at very least repeated warnings about drawing conclusions.
Incidentally, this idea that "you" come from a certain region is only correct if it is expressed, as was the case in another previous programme, along the lines of "your ancestry appears to be 60% from region A, 30% fromregion B, with a soupcon of 10% from region C"!.......
The scientific method is not that straightforward to understand if you don't have the advantage of the associated education, together with a bent for such subjects and interest in them. See after my signature for an interesting situation !!
What has totally inflamed me about the Gene Detectives programme has been that very strong suggestion, or at least implication, that photographs i.e. physical appearance, voices, physical quirks such a tongue bending and tongue nose touching, as well as general health characteristics can be a valuable tool in seeking relatives.
I'm in no way denying that any of these aspects can be fascinating in terms of adding to the situation, but there's no way at all that they should be used as research criteria.
The nature of human reproduction is such that chromosomes, and therefore genes, get shuffled about. Yes, it's quite possible that you are the spitting image of your father, or maybe uncle Jimmy (which, of course, in genealogical research terms can raise a warning flag
), but the fact that you are not the spitting image of your father or uncle Jimmy is equally likely in terms of how the genes get shuffled, and various genes change from dominant to recessive, and the reverse.David
An Interesting Situation
You're out on a walk.
Part of the walk takes you across a golf course.
As you approach the fairway on one hole, you see that a foursome are about to drive off from the tee, and stand back at the side of the fairway.
One of the drives lands only a few feet away from you.
You muse "Hmmmmmm..... the chances of the golf ball landing on that blade of grass must be at least several million to one; therefore the golfer must have aimed at that particular blade of grass".
So where's the logical fallacy in this argument?
dww
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