In humans there is a pair of chromosomes in which one component is an X and one can be either X (a female) or Y (a male). A baby gets one of the pair from his mother and one from his father. If she gets an X from each parent she will be female (two X's). If he gets an X from his mother, but a Y from his father, he will be male (an X and a Y). The Y is the male chromosome and determines that the baby will be a male. Thus, the Y chromosome is passed down unchanged from father to son. For this reason it serves as a surname marker – in the line from Leonard to the present, for example, every male named Harriman will carry the same Y chromosome.
Occasionally, though, there are mutations and the chromosome changes slightly. These changes are statistically predictable and can indicate generations. Two Harrimans would have identical Y-DNA (chromosomes) if it weren't for the mutations. But because of this, it is possible to estimate how many generations have passed since there was a common ancestor. Thus, if two living Harrimans are found to have identical markers (the indicators within the Y-DNA that may change), then they must be closely related – how close depends on how many markers are tested. If their Y-DNA differs by only one or two markers, we can estimate how far back the common ancestor lived. Conversely, if their Y-DNA differs by more than two or three they cannot be related within hundreds of generations, despite carrying the Harriman name. (We are always cautioned that adoptions and illegitimacy can appear where not expected).
In genealogy, there are three main uses for Y-DNA testing: to provide additional proof that existing lines are correct, to connect someone to a known line and to show that someone does NOT belong to a known line. The requirement, of course, is that there must be living males of the Harriman surname, some of whose lines are well known through many generations.
As you can see, our Harriman Family organization meets all of these conditions. We have initiated a Harriman/Herriman/Harryman surname Y-DNA project. There are three levels of test for 12, 25 and 37 markers. Normally it is desirable to start with the intermediate level of 25 markers (the test can be upgraded later for a small additional charge and using the original sample).
Oh, oh, I hear you say – what kind of a sample? It is quite simple – the kit contains a swab - sort of like a hard Q-tip - and you scrape the inside of your cheek. The resulting swab is placed in a sealed tube and sent to the testing lab. The kits contain everything needed, including instructions, mailer and release forms. As part of a surname project, the cost is $169 for the 25 marker test. A 12 marker test for $99 should be sufficient to show whether there is or is not a connection to our Harrimans, but may be ambiguous and won't tell much about how close the relationship is.
Obviously, this is a really brief summary of the process.
If you are now completely bored, you can stop reading here. If you are thrilled to death, I give a little more detail in the following.
A little more detail
While molecular genetics is not a simple subject, some of the confusion comes from, in my opinion, poor use of terms. There are four basic building blocks – chemical components called bases. They are adenine (A) and guanine (G), thymine (T) and cytosine (C). They are put together into long strings forming a molecule called DNA. These strings occur in pairs and are joined together to form the famous double-helix of DNA. Chromosomes consist of a string of DNA and other material to make a package. In genealogy we often hear of Y-DNA and Y-chromosomes – they refer to the same thing. In humans there are 23 pairs of chromosomes of which one pair controls the sex of the human. Females have a pair of X chromosomes, but males have a pair consisting of an X and a Y. When the chromosomes are passed to an egg, one of each pair comes from the father and one from the mother. The X chromosome of the child can come from either the father or the mother, but the Y can come only from the father. So the child will have at least one X, but will then have either another X (and be female) or a Y (and be male). So if you have Y-DNA, you not only must be male, but you must have obtained it from your father. And he could get it from only one place – HIS father. Not only that, but the sequence of nucleotides (the packages that contain the bases) on the DNA remains unchanged. So your Y-DNA will be identical to that of all your male ancestors in your surname line. Certain patterns appear in the sequence of nucleotides and some stretches along the DNA molecule carry hereditary information and are called genes. But large sections of the DNA have no apparent purpose and are called "junk" or non-coding DNA. This is what is used in genealogical testing. For that reason the tests cannot be used to obtain medical information. The information cannot be used to tell anything about the physical makeup of the person; it can only tell about relationships. If two people have the same sequence of nucleotides, they must have the same ancestor. To make things more interesting, every once in awhile there is a mutation and the Y-DNA changes between the father and son. This is rare, but can be statistically predicted. And it only occurs on one of the markers at a time (markers being the places on the DNA that are specifically chosen as standards for these purposes). Therefore, we can make inferences as to how far back two people with slightly different patterns shared a common ancestor.
Here is a sample showing two people with a 25 marker test. The allele values are the indicators on the DNA. The bottom row shows the difference between the two sets of alleles – more than a single number other than 0 indicates that they are not related in any way – despite having the same surname. These two people are unrelated.
|
Markers |
3 |
3 |
1 |
3 |
3 |
3 |
4 |
3 |
4 |
3 |
3 |
3 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
4 |
|
Alleles for person A |
13 |
24 |
14 |
11 |
13 |
14 |
12 |
12 |
11 |
13 |
13 |
29 |
18 |
9 |
9 |
11 |
11 |
25 |
15 |
19 |
28 |
15 |
16 |
17 |
18 |
|
Alleles for person B |
13 |
24 |
15 |
11 |
14 |
15 |
11 |
13 |
13 |
13 |
11 |
30 |
18 |
8 |
10 |
11 |
11 |
26 |
15 |
19 |
31 |
14 |
14 |
15 |
15 |
|
Difference between person A and B |
0 |
0 |
1 |
0 |
1 |
1 |
1 |
1 |
2 |
0 |
2 |
1 |
0 |
1 |
1 |
0 |
0 |
1 |
0 |
0 |
3 |
1 |
2 |
2 |
3 |
At the web site http://www.dnaheritage.com/tutorial2.asp is a pretty good tutorial on DNA used in genealogy.