Understanding the Concepts Involved in a DNA-Study.
Understanding the concepts involved in the DNA study have been quite a learning experience for me. Many of them are quite complex and can be daunting. I'm aware that this can put people off and that not everyone wants such details. There are a number of rudimentary concepts that are necessary to one's understanding of the study and I believe will enhance not only one's understanding but pleasure in the study. The following links are my attempt to put these concepts in an easy to understand format. In each are links to more complex explanations for the more brave hearted.
Section a)
Some concerns re. DNA testing:
I think the idea of taking a DNA test raises a number of fears for people. This largely rests on the kinds of DNA tests one hears reported in the media. Thus, before discussing the purpose of DNA studies it may be worth discussing what they do not do:
They "tell you nothing definitive about your medical history or your skin colour, and ...can't provide a racial identification as 'race' is a social construct.....Although some people are concerned that their DNA data could be misused by a laboratory in some unspecified way, there is ...no danger that this will happen as laboratories are bound by strict confidentiality rules.......results are not medically informative and will not provide a unique personal identification such as the police would use for the detection of a crime" . I've taken this from a number of reputable articles on the issues.
Neither do the tests involve taking blood......for those who are squeamish.
Objectives of the Study Include:
1) Identification of others who are related and possibly degree of kinship.
2) Proving or disproving theories or Myths regarding ancestors.
3) Solving brick walls in research.
4) Determining locations for further research.
5) Validation of existing research.'
Family history has many aspects but at it's core is the identification of ancestors. Having identified potential ancestors there are two tasks. One, eliminating possible contenders. Two, finding proof that possible contenders are in fact our ancestors. The latter has traditionally been evidenced by a 'paper trail'; documentary evidence, preferably from original sources. Documentary evidence in the form of birth certificates, wills etc. These are only as truthful as the person reporting the information. "Rarely is actual 'proof' forthcoming. Thus, the task involved in constructing a pedigree which stands up to scrutiny, is to take all possible steps to eliminate a candidate from further consideration before accepting that he or she can be added to the top of the line", (64) There is increasing evidence that documents are often, sometimes deliberately misleading. Estimates of 'non-paternity' events, the recorded father not being the genetic father, vary widely from 5-30% (64).
We have an advantage that early genealogists did not have. DNA tests are a new weapon in our armoury which may "enhance the research process of compiling evidence ... 'test' the accuracy of a pedigree" (64). We can utilize a process called Triangulation. Based on paper research we can identify two of more lines of descent from different sons of a shared ancestor. DNA can confirm their descent from this ancestor. The next step is to expand the base of the triangle outwards, and the apex backwards, and pursue the objectives outlined above.
Analysing data: certain markers are found within areas of DNA, known as junk DNA. These are strings of proteins, which are repeated. These markers are called loci and assigned names ie DYS 338. The repetitions are counted and assigned a number ie DYS 13. Tests can be for various numbers of markers eg 12 to 43. The combined pattern is called a Haplotype. Individuals results are compared marker for marker. The more markers that are tested, the more sensitive and definitive the results. If a marker differs by one repetition this is said to be a one-step mismatch or a genetic difference of one eg DYS 338/13 compared to DYS 338/14. If the repetition differs by 2 eg DYS 338/13 to DYS 338/15 this is a genetic difference of 2. Likewise if two markers differ each by one this is a genetic difference of two.
Using statistical analysis combining the numbers of markers, the genetic difference and a knowledge of marker mutation rates enables the Time to the Most Recent Common Ancestor (TMRCA) to be determined. The results are described in terms of the percentage probability of being connected within a number of generations or years. This could be 25% chance of being related within X generations, 50% chance etc.
Section b)
1) The Science:
a) The DNA tested. click
here
b) How to read the test results. clickhere
2) Relationships:
a) Deep and distant ancestry ie Haplogroups & Haplotypes. clickhere
b) Time to Most Recent Common Ancestor (TMRCA). clickhere
c) Triangulation. clickhere
* Some guidance on choosing a) numbers of markers b) testing company.
this is usually in the form of a mouth swab. Swabs from the test kit are taken and sent to laboratory. The companies currently being used are http://www.familytreedna.com/ and www.ancestry.com . The tests being conducted on the family lines are y-chromosome tests [y-chromosomes are only passed down through the male line which is very helpful in tracing surnames]. In other words, your y-chromosome came from your father and his from his father and so on. Hence the reason for asking male holders of the surname. Individuals with the same genetic code and with similar numbers of repetition of this code at specific marker loci are believed to be related and to descend from a common ancestor. The tests cannot tell you who your precise ancestor might be, but they will tell you that your DNA clusters with a group of other individuals and that this cluster of individuals likely descend from a common ancestor at some point in the past. The test results are reported in terms of the cluster your DNA fits with. However, the tests do tell you who you are NOT related to. 
