DNA, Y Chromosome Testing, Haplogroups, Paleolithic Hunter gathers, Population Genetics
These pages attempt to explain how modern developments in DNA profiling can help us unravel more information about our distant past. It will also help any living and participating male Dowie's establish the probability of a common ancestor with other participants. For reference the results of your web master's DNA test are given below and compared to other results obtainable on the web.
Deoxyribonucleic acid - DNA - is present in every living cell & contains the blue print for life. Twenty three chromosomes carry the genetic instructions that defines who we are and why we have the characteristics we do.
DNA consists of two strands that wrap around each other to resemble an incredibly long twisted ladder. The sides of this "ladder" are made from sugar & phosphates molecules, the rungs are made from nitrogen containing chemicals called Bases. Each strand is made from one base, a sugar molecule and a phosphate molecule. There are four bases ( A adenine, T thymine, C cystosine, and G guanine ) which pair together AT & CG as Base Pairs; the order that they create along the phosphate "backbone" is referred to as the DNA Sequence. It is the patterns that these base pairs form that is the basis of Y chromosome testing.
Chromosomes are paired packages of long segments of DNA. In humans there are 23 pairs of chromosomes, in 22 pairs each member is essentially identical, one being inherited from each parent. In Males & Females the 23rd pair is different; females have a pair that are alike - called "X" and males have two very dissimilar chromosomes called "X" and "Y" When a child is conceived it gets one chromosome from its mother - always an X, and from from the father - which may be X or Y.
It is the presence of the Y Chromosome that determines male sex. As such it is only transmitted from father to son, and mostly is inherited without alteration through the generations. It is the only chromosome that escapes the continual reshuffling of parental genes and makes it so useful to genealogists.
Y Chromosome Testing
The Y-Chromosome has definable segments of DNA with known genetic characteristics. These segments are known as Markers. These markers occur at an identifiable physical location on a chromosome known as a Locus. Each marker is designated by a number (known as DYS#), according to international conventions. The Marker is what is tested and the Locus is where the marker is located on the chromosome.
Although there are several types of markers used in DNA studies, the Y-Chromosome test uses only one type. This type is called a Short Tandem Repeat (STR). STRs are short sequences of DNA, (usually 2, 3, 4, or 5 base pairs long), that are repeated numerous times in a head-tail manner. Simply put, those markers are places on the Y-chromosome where the DNA "stutters". The sequence at that point repeats a certain pattern over and over. For example that stretch of the DNA molecule might look like: GATA GATA GATA. It is the variations in the number of these repeats which enables discrimination between individuals.
Several genealogical genetic testing labs are now selling kits that will allow one to take a cheek swab and return the sample for genetic testing. The tests return a "score" on a conventional set of markers. Those special "stuttering" locations are given names like DYS391 or DYS455. Each of the numbers that you get back in your Y-chromosome test result refers to how many times a pattern is repeated at one of those markers. The example above would return a value of "3" in your Y-chromosome test results. The number of repeats is referred to by geneticists as the alleles of a marker.
An individuals results are referred to as their Haplotype. Similarities are discernable and represent common ancient origins. In this way a set of similar individuals haplotypes can be compared and grouped together to create a modal Haplogroup.
Normally the Y-chromosome pattern is handed down unchanged from
a father to a son. But occasionally small changes can happen in the copy of the
Y-chromosome that the son inherits. The changes that occur at STRs are that the
stuttering sequence ends up being longer or shorter in the number of repeats
than the father has at that location. (Usually only differing by one). The son
later passes that modified version on to his own sons. These mutations (changes)
don't happen very often. A marker will only undergo one of these mutations once
in about 500 generations. But that means with 25 markers we might expect to see
a change in one of them within about 20 generations (about 500 years). That time
frame is what makes them useful to genealogists. Since surnames have only been
in use for 700-1000 years we don't have much interest in connections with others
any farther back than that. These mutations mean that any relations from farther
back than that will have a different sequence of numbers, whereas closer
relations will still have almost the exact same sequence of 25 numbers.
Genealogists are interested in finding connections between families on a time scale of centuries, and the mutation rate of STRs is such that they are a good choice for that kind of work. Population geneticists are interested in tracking the movements of groups of humans over time scales of 1000's or 10,000's of years. Therefore their studies usually involve a different type of Y-chromosome marker known as Unique Event Polymorphism (UEPs) which have a much slower mutation rate than STRs.
As mentioned above Haplogroups are defined by patterns seen in the values of these slowly mutating markers. Identification of your Y-chromosome haplogroup can provide an interesting glimpse into the deep ancestry of your paternal line.
A test of UEPs would be the only way of identifying one's haplogroup for certain - but no commercial genetic testing laboratories offer that service at the present time.
However some conclusions can be drawn about haplogroup classification by looking just at the STR marker value patterns. A good rule of thumb for determining haplogroup is the following:
If you have...
DYS426=12 and DYS392=11 then you are probably a member of haplogroup 3 (HG3).
DYS426=12 and DON'T have DYS392=11 then you probably belong to HG1.
DYS426=11 then you probably belong to HG2.
DYS426=11 and DYS388=12 then you may belong to HG16 or HG21.
There will be exceptions to the above rules - but this method works well for most men whose paternal line is of European descent.
One common Haplogroup is Hg1 (Haplogroup 1), which is characterized by a commonly known haplotype called the Atlantic Modal Haplogroup (AMH, haplotype 1.15). This haplotype is most commonly found along the Atlantic coast of Europe. While the definition of these different haplogroups are based on a different set of test markers, there is a significant correlation with haplogroup tests and the markers in your test. If your results match or very closely match the AMH values, there is a very good chance your paternal ancestors came from this region.
Other common makers and values for AMH are:
A lack of differences is also unique. In a study of 340 samples, only one was an exact match with its haplogroup's most common values. Unfortunately Haplogroup classification is fairly useless for locating the place of origin of your paternal line. While each haplogroup has general areas in which it is more common, there has been enough mixing of people on the European continent to prevent using these classifications to pinpoint any single place of origin.
The members of HG1 are thought to be the descendants of the Paleolithic hunter-gatherers who arrived in Europe before the last Ice Age about 40,000 years ago (Aurignacian culture). That pattern is most common in Western Europe, but is also found in all other parts of Europe. The members of HG2 are believed to be the descendants of two later waves of humans into Europe. The last of these waves arrived about 8,000 years ago and is credited with introducing agriculture into Europe. HG2 is most common in Southern and Central Europe, but that haplogroup is also often seen in those of Anglo-Saxon and Scandinavian descent. The haplogroup HG3 is seen more frequently on the eastern side of Europe. But HG3 is also common in Scandinavia, and is said by some to be indicative of "Viking blood" when seen in paternal lines originating in the British Isles. The forefather of all HG3's is thought to have been born in the Ukraine during the last Ice Age about 15,000 years ago.
Keep in mind that haplogroup classification is fairly useless for locating the place of origin of your paternal line. While each haplogroup has general areas in which it is more common, there has been enough mixing of people on the European continent to prevent using these classifications to pinpoint any single place of origin.
Population geneticists look at a different kind of marker, known
as a UEP - Unique Event Polymorphism. The marker in this case involves a smaller
part of the DNA. Often the change involves just a switch in a single letter in
the DNA - known as an SNP (Single Nucleotide Polymorphism). For example a "C"
might have been changed to a "T". SNPs have names like M170, M89, or SRY-2627.
UEPs are the markers that are NOT presently available from commercial testing
companies - so you won't find those names anywhere in your Y-chromosome test
UEP mutations are very rare - on the order of once in 100 million generations. The reason that they are ever seen at all is that they can happen at any of the billions of letters that go into making up the whole DNA molecule. Once a UEP has occurred, all the descendants of that first man will also show that same mutation. The definition of a haplogroup is the group of all the paternal descendants of the single person who first showed that UEP mutation. Each member of a haplogroup will have the same UEP mutation that first appeared in the haplogroup's founding father - along with the whole set of other UEPs that the founder himself had inherited from his forebearers. Since these mutations are so rare, it is almost impossible that a second mutation would occur at the same spot to undo the UEP mutation back to its original state. So UEPs are the ultimate "permanent record". This is what allows population geneticists to identify the descendants of a group of people over periods of tens of thousands of years.