This discussion of the genetics of DNA testing has been deliberately simplified. The hazard of doing so is to misrepresent the facts. We apologize in advance for any such misrepresentations. Anyone interested in a more technical and scientifically correct explanation is encouraged to follow the links provided in More About DNA on this website.
Although genetic research is not new, its use in genealogy is relatively recent. This application has been given the name "genetic genealogy." It is the branch of knowledge arising out of the study of genes first identified in 1909 for identification of inherited physical characteristics. Later, it was found that deoxyribonucleic acid (DNA) was contained in chromosomes and acted as a carrier of genetic information. Since 1940, the chemical nature of DNA has become a science revealing more and more of the mysteries that make up the human body. It now has become a science that permits the identification of individuals by the use of DNA.
DNA is used widely in criminal investigations, court proceedings in paternity cases, and other issues requiring individual identification. Talk shows and other media have popularized identifying fathers of children using DNA.
Professor Bryan Sykes of Oxford University in England made headlines several years ago when he reported on the results of his research using mitochondrial DNA samples. More recently, the analysis of the Y-chromosome has been used in genealogical research. Y-chromosome testing offers the advantage of being found only in males. Thus, a father-son relationship following a single surname can be traced through multiple generations.
At this time, the Beatty DNA Project deals only with Y-chromosome testing. Only male subjects are used in Y-chromosome testing because of the genetic distinction between females and males. Females have two X-chromosomes, one of which is inherited from her mother and the other from her father. Males have one X-chromosome, from his mother, and one Y-chromosome, from his father. In the laboratory, the two X-chromosomes of the female cannot be distinguished from one another. However, in the male, because the Y-chromosome is a different length than the X-chromosome, it can be distinguished from the X-chromosome. And, since the Y-chromosome is inherited from the male's father, it is, generally speaking, an identical copy of the father's Y-chromosome (except for certain changes described below).
The mitochondrial DNA which is also used in certain types of genealogy research does not come from chromosomes at all. It is derived from parts of the cell outside the nucleus (where chromosomes are found). Both males and females have mitochondrial DNA. It is inherited from the child's mother, and she inherited it from her mother. Thus, this line of research does not follow a surname descendancy. Mitochondrial DNA is more expensive to analyze in the laboratory. And the results are much more difficult to interpret than those from Y-chromosome testing.
In a laboratory using special equipment, scientists are able to identify and 'measure' different elements of the Y-chromosome. These elements are called markers. As of today, 111 separate markers have been identified for an individual Y-chromosome sample by the laboratory doing our DNA analysis. Additional research will probably identify more markers in the future.
For each sample, laboratory analysis can determine a 'value' of each of these markers. This 'value' is basically a 'measurement' of each marker. For example, the 'value' of Marker #1 might be 13, for #2 it might be 24, for #3 it might be 15, and so on. (Remember, this explanation is a gross simplification of a very complex subject.)
Ordinarily, the value of each marker of a father and his biological son is identical. In the above example, both father and son would test #1=13, #2=24, #3=15, (and so on through the number of markers tested).
Occasionally, a change occurs in one of these markers between a father and son. These natural, but infrequent, changes are called mutations. For example, if one of the markers described above (say, #2) mutated in the son, then #2 might be 24 in the father and 25 in the son. If that son had a son of his own, his son's #2 marker would also be 25. The mutation could be down one number (to 23) as well as up one number.
It isn't known how often these mutations occur. Current scientific estimates indicate that many generations elapse between significant mutations. These mutations do not occur in a neat and orderly manner. Recent evidence indicates that some markers may mutate more frequently than others.
Value of Mutations
What is important in genealogy is that such mutations do occur. And, it isn't the number assigned to each marker that is important; it is the comparison of a set of numbers from one sample with those of other samples.
For example, let's say six participants named Jones produced 4-marker test results of #1=14, #2= 22, #3=15, and #4=10. Since these six males have identical values at each marker, one can conclude that they are closely related. It wouldn't mean they are father and sons, or that they are brothers, just that they are closely related.
Now, let's say a seventh participant named Jones produced 4-marker test results of #1=13, #2=21, #3=13, #4=11. Because these results are so different from those of the first six participants, one can conclude that this person is not closely related (genetically) to the other six (and might not be genetically related at all).
Other Reasons For Differences in Numbers
In addition to naturally occurring mutations, there are several other reasons why one set of numbers might be different from others within a family group. One of these is adoption. Historically, it was not uncommon for a male to adopt the child, or children, of others and raise them as his own. Looking back several hundred years and considering the hazards of everyday living (accidents, diseases, wars, etc.), it isn't surprising that many orphans needed caring for. These may have been the children of a wife's sister, or of a neighbor. Adoption procedures may have been quite simple; the child or children just assumed the name of the adopting father and that was that. Of course, the adopted boys carried the Y-chromosome of their biological fathers, so there would be little or no similarity to their adopted surname.
Another reason for differences involves illegitimacy. It's a subject that no one wants to admit might have occurred in their ancestral past, but, although probably rare, such occurrences did happen.
Finally, there may be instances where a man simply changes his name, for whatever reason seems important to him. Thus, although he assumes a surname being tested, his Y-chromosome test will not correlate with those that are a biological part of that surname group.
If any of these circumstances occurred 12-15 generations ago, the correct explanation is probably lost to history.
A Word For The Cautious
Some may worry that these DNA tests might reveal medical conditions or other personal information. The truth is that the Y-chromosome tests are not made on regions of the cell that are used for medical diagnostic purposes. Those are tests of a different type for which other regions of the cell are used.
Also, Y-chromosome testing is not the kind of analysis that might identify physical characteristics, or prove a paternity, or link a suspect to a crime scene. Those kinds of DNA analysis are totally different from the Y-chromosome testing we are using.
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