THE CHILVERS DNA PROJECT - PAGE 2   

TIME FOR SOME SCIENCE

Right! You've got here from the first page about the DNA project and would like to know what the background science is. I'll try to explain in simple terms - there are loads of more complex (and complete) explanations out there on the Web.

All humans have a pair of sex chromosomes - molecules of DNA - in each cell. Men have an X chromosome and a Y chromosome. Women have two X chromosomes. This XY or XX arrangement is what makes us male or female.

The genetic material, the DNA, is passed from one generation to the next pretty well unchanged. It is obvious though, that the Y chromosome information can only come from the father, because your mother doesn't have any to pass on. In other words the paternal DNA information is passed on straight down the male line. Just like your surname, in fact. By looking at information in the Y-chromosome we can find family links, especially in single-name groups - like CHILVERS!

Genealogical DNA-testing looks at areas of DNA in the Y-chromosome called "junk DNA". These are areas of the chromosome that have no identified purpose. In fact about 98% of the human genome is considered "junk DNA"! The relevant point here is that a genealogical test will not stir up concerns about medical disorders etc. The areas being tested don't tell anything about the person being tested's health, colour of eyes, likelihood of having some disease or other, their IQ or whatever - it just provides data that can be used to compare with someone else to ascertain if there are family links in the past.

Haplotypes

At varying specific identified points along the DNA strand (loci) occur what are called Short Tandem Repeats (STRs). These are places where a sequence of the molecules that make up DNA repeat a number of times. By counting these repeats we get a series of numbers for an individual. Genealogical testing starts at about 12 sites (markers), but for better results we need 25 or 37 markers. These individual groups of figures form your haplotype.

The results look something like this:

Now comes the clever bit. I said before that the Y-chromosome information is passed from father-to-son pretty well unchanged. So it is. But occasionally, just occasionally, the sequencing goes a bit odd when it's transferred down the line, and instead of the pattern repeating say 15 times, it only repeats 14 times. This is called a "mutation". Some of these markers more readily mutate than others (DYS464 is the most-varying for example, while DYS454 is the least varying - neither appear in FTDNA's 12-marker test). Obviously if you have identical matches over say 37 markers then there is almost certainly a direct paternal-line link. But the odd mutation or two may indicate branches of the family, and just means that the point where the branches of the family join are that bit further in the past. The balance of course is between having a few mutations that mean the MRCA - the Most Recent Common Ancestor - is further back and having so many mutations that effectively there is no link.

So in our example above we may have someone with:

The great use of a 12-marker test is for elimination "on the cheap". Maybe we have:

Right? Are you still with me? This is the most obviously useful part of the DNA testing - and for the CHILVERS family it may provide us with all sorts of information about our family. But we need loads and loads of information to compare, so if you know of anyone who may want to take part please either follow the various links or just send me an e-mail.

Haplogroups

There is another bit of genetic information that can be obtained - and that's called a haplogroup. There are some mutations that occur so rarely, and are so monumental,that they are likely to have occurred only once throughout history at any particular site on the genome. Not like the mutations we've talked about above, which occur maybe every few generations or so, but once ever! "Huh? And so?" I hear you say.

Man - Homo sapiens sapiens - developed in the plains of East Africa about 60-90 thousand years ago. As time progressed Man started to move away from that base, and along the way some of these monumental mutations occurred. These mutations put modern humans into a variety of groups linked with those mutations - called haplogroups. Haplogroups A and B, for example, are the oldest haplogroups in the world, and are only found in sub-Saharan Africa (or in societies coming from there, eg by the Slave Trade). As Mankind spread throughout the world other mutations occurred at varying times. Two that interest us, as CHILVERS maybe, are a mutation that occurred in Central Asia, near modern Kazakhstan, about 20-30 thousand years ago. This gave rise to a haplogroup called R1b, which spread westwards into Europe, but groups of which became isolated in the Iberian peninsula as the Ice Age once again took hold. When the ice retreated this group spread out through western Europe and this haplogroup now represents 70% of the population of southern England (and actually about 90% of Spain, Portugal, France, Ireland and Wales!!). One form of this haplogroup is what's called the "Atlantic Modal Haplotype" which is at its highest frequency in the Iberian Peninsula and the British Isles.

Another group however seems to have headed northwards as the ice retreated about 45 thousand years ago, and are marked by a haplogroup I1a. This haplogroup is very prevalent in Scandinavia, and is considered where it occurs in the English population to be indicative of Anglo-Saxon or Viking descent.

Haplogroup identification, to be exact, requires a different type of DNA-testing, called Single Nucleotide Polymorphism or SNP (pronounced "snip"). However, it has been discovered that STRs as discussed above can, in most cases, give a good indication of the haplogroup. Some markers mutate at quite a fast rate, so are useful in looking at more recent events, while others are so slow that they can be indicative of a haplogroup. DYS455=8 for example is considered a good indicator of haplogroup I1a - the Anglo-Saxons - because it is rarely (if ever) found in people in other haplogroups.

We know the CHILVERS are from East Anglia, where the Anglo-Saxons lived, and CHILVERS is an Anglo-Saxon name. But are we actually directly, through the male line, Anglo-Saxon, or has there been some "dilution" along the way? We all know what those Normans were like!! All very interesting whatever the results.

This is as far as I'm going to go on the explanations at the moment, but if you want to know more go to Wikipedia and search for "genetic genealogy" and follow the links. The more of us who can put our heads together to interpret what we find the better !!

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