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 DNA Details and Definitions

It would be helpful if you first read "DNA Jam?sons - We're Not All Related" before continuing with the more detailed informations and definitions below. The background information on that page will help to make some of the terms and explanations of details listed here clearer and better understandable.

As generally described on the above related page, we with this website are primarily interested in the information contained within the Y-DNA chromosome. This is the chromosome that contains mostly unaltered information handed down from father to son, from generation to generation, since the beginning of mankind. Although examining this information can tell us any number of anthropological things, we here are really mostly only interested in how this will let us determine who belongs with what family. Although this is really a fairly simple matter, it is somewhat difficult to explain, without over complicating things. As an example, there is a contradiction in explaining that we can really only do what we most want to do, categorize different families, only by determining the differences in the very thing we say is handed down "unaltered" for thousands of generations. The truth is there actually are differences, but they are minute and occur mostly over hundreds and/or thousands of years. These changes (mutations) are scientifically very difficult to detect and evaluate. However, for our purposes, we don't really need know the science part, only the results and how they compare (match) from test to test, and therefore person to person - and by extension, family to family..

Most Y-DNA test results are explained in numeric form which relates to the number of times a gene is replicated and in what location. Without having studied this sort of thing in detail, the average person is unlikely to be anything but bewildered and confused. Say nothing of the ability to analyze the results into a coherent and understandable conclusion.

That's the bad news. The good news, really good news, is that to use this information with genealogy, you don't really need to be be a genetic scientist, or to even know that much about DNA science. If you learn the basic terms and have a overall understanding of what you are trying to do, combined with a somewhat reasonable sense of science, you'll do just fine with the results and analysis handed to you by all the responsible testing labs, and genealogy projects, like us.

Apart from doing an actual test, DNA as used by the genealogist or family historian, is in it's most basic form, a comparative science. You compare one test to another - if you match, you are related. If you don't match, you're not related. Most Y-DNA tests are made up of two different, but somewhat related parts. One part of the test is that of a series of "STR"[1] markers[2]. These are considered fast changing (mutating) markers, maybe one every 100 years, or so. These are expressed in numbers, at a series of "DYS"[3] locations. You should not be concerned by either of these terms, they are simply scientific terms used to explain how your Y-Chromosome is constructed. For genealogical purposes you need not really know the science behind these terms, only that they represent something that when compared to someone else's similar numbers, can help determine personal relationships. The larger number of places (markers) you match exactly, the closer your relationship with the other tested person.. Most experts believe that you need to test for about 25 markers at a minimum, with 37 marker test, or more, just about right - more even better. Truth is, if you don't match in the first 12 markers, you're not going to be a match (related) no matter how many more markers with which you attempt to match.

There is also an element of anthropological information to be gleaned from a Y-DNA test, and this too is not something you can determine or understand on your own. You must compare your results to those results of as large a group as possible, already tested. Again, this is an area for experts, not individuals, and again this is really easy to do. This is the second part of every Y-DNA test and what is known as your "Haplogroup." A Haplogroup is a broadly defined category of of results based on a series of what are known as SNP[4] markers found in your Y-Chromosome. These SNP's are slow, maybe every thousand years or so, mutating (changing) markers, which by their nature, allow scientists to say, with reasonable certainty and based on statistical information, when those families with certain SNP's were formed. Everybody is classified into a widely based Haplogroup, made up from a series of agreed on SNP's and characterized by an alphabetic label (A to Z), which is then followed by various alpha-numeric series of numbers based on a series of additional unique SNP's found in your Y chromosome. So far, all Jam?sons tested have fallen into one of two basic Haplogroups, either "R" or "I" (eye), both fairly common. There are however several subgroups within each of these general Haplogroups, most of which we recognize, with various degrees of distance as separate and different families.

Y-DNA testing, can get a lot more complicated by those interested in further defining families or specific relationships. But it need not be so, for the majority of us primarily interested in just determining what particular Jam?son family we belong with, or don't belong with.


[1]      "STR" is an acronym for "Short Tandem Repeat" a scientific term used to identify a series of short term (hundreds of years) markers (DYS numbers) in Y-DNA testing and analysis.

[2]      "Marker" is actually the location on the chromosome and the 'number' is the number of times it is repeated.

[3]      DYS is an acronym for "DNA - Y-Chromosone - Segment" - and is basically referring to a collection of STR locations, usually along with the number of repettive returns at that location.

[4]      "SNP" is an acronym for "Single Nucleotide Polymorphism" a scientific term used to identify a series of long term (thousands of years) markers in DNA testing and analysis, usually for the purpose of determining a Haplogroup.