By Kathy Hughes
Contributing Writer
Anyone considering having a DNA test, should know that what is being advertised is not a medical test. The methods used may be the same, but the results are interpreted differently. Commercial DNA tests provide you information about your relatedness to other contemporary people in your community and the world; additionally, test results can reveal your relationship to people living in the ancient past.
There are three DNA tests available commercially: autosomal, mtDNA (mitochondrial) and Y-chromosome. Autosomal testing was discussed in a previous article, but it tests DNA inside the nucleus of your cells, on the chromosomes.
Considering, the mtDNA test, it examines the DNA outside the cell nucleus on the mitochondria. Mitochondria exist outside the nucleus, in the cell’s body. An egg provides a good analogy, with the egg yolk and the egg white. Mitochondria occur in what would be the egg white, not in the yolk, or by analogy, nucleus. ( This analogy works to explain and visualize the topic. It is not a scientific explanation.)
Y-DNA testing only applies to men, that is the DNA carried by men on their Y-chromosome. The Y-chromosome determines male gender.
A common factor about these two DNA tests is that they trace heredity back into the ancient past. The DNA in these cases changes only rarely, even over centuries, or thousands of years.
As children are conceived, these DNA components behave differently in males and females. Only men inherit the Y chromosome from their fathers, instead of the second X, as for women. Therefore, all men with identical Y-chromosomes are descended from one male. Or, put another way, men pass their Y-chromosome to all their sons, down through time (and millions of men). The slight differences in Y DNA allow scientists to group men who are all descended from the same father together.
The mitochondrial DNA is inherited completely differently. Recalling the analogy of the egg — the mitochondria exist outside the cell nucleus (yolk), that is in the egg white. While the nucleus of a cell has DNA from both parents, the DNA outside the nucleus comes from the mother’s egg, for both her sons and daughters.
The chain of mitochondrial inheritance allows us to trace the mother’s line back through the generations of women into the ancient past. At present, only seven different mitochondrial types have been identified. The stunning conclusion is that everyone’s mtDNA originated from one of these seven women. In turn, these seven women were all descended from one woman — not surprisingly, this woman is referred to as Eve.
Whether two people are related on their maternal side, can by identified by mtDNA testing; however, which maternal relative you have in common can only be identified through intensive research of existing records. Contrary to what advertising suggests, this intensive research rests on your shoulders — the company will not do this for you.
If you are lucky enough to have a living male relative willing to be tested (or if you are male), and your DNA match is also a male, Y-chromosome testing can prove whether you are related through the paternal line or not.
To review, deciding to have DNA testing, which test you have, and in what sequence depends on what you want to learn, and how much research you are prepared to do on your own. Ideally, if you want to research a family tree, as well as find living relatives, all three tests are useful, but begin with autosomal test. Your research may require a considerable commitment of finances and time.
