Introduction to DNA Testing

Introduction to DNA Testing
By Dale E. Lee


  • Why take a DNA Test?
  • Different Kinds of DNA tests
  • Mitochondrial Testing
  • Y-chromosome Testing
  • Autosomal DNA Testing
  • X DNA Testing
  • What test to use?


Why take a DNA Test?

DNA testing is not for everyone. There are privacy concerns involved in testing, and the results of testing may not reveal the information you needed. But sometimes, they are an invaluable aid in discovering relationships that are difficult to determine because of the lack, or locking, of records. Records can be destroyed over time and they can also be locked during the adoption process if the biological parents don’t want the child to know who they are.

The search for matches on DNA can be helpful for both climbing the Family Tree and descending it.

I have a friend who got involved in Family History, and as part of his involvement, turned in a DNA test to Ancestry and found he had a daughter he didn’t even know existed. She had also done a DNA test and contacted him when a match was found… from Australia. He confirmed the relationship, and now he has contact with a part of the family that he hadn’t known about.

I currently need to prove that the information we have on an early American ancestor came from where we think he came from in the old world. It is possible that through DNA, we may be able to prove a connection to a lateral line that stayed in the old world. If this is true, we may be able to get around the lack of documentation we’re currently facing.

The following is based on the RootsTech course on DNA Basics and research on the internet. I have not been paid for publishing this article nor am I currently affiliated with the companies mentioned in the DNA Basics course as of this writing, but may do so in the future.

Different Kinds of DNA tests

Most people don’t realize that there are different kinds of DNA tests. And each type of testing is used to prove different things as far as biological relationships are concerned. The overriding factor is to use the type of testing to give you the best answer for the question you are trying to answer. Many people take the DNA tests not knowing there are differences and may not find what they are looking for.

The following are the main types of testing currently being done:

  • Mitochondrial (mtDNA: Mother’s line)
  • Y-chromosome (Y-DNA: Father’s line)
  • Autosomal (AtDNA: Combination Mother and Father)
  • X DNA (Combination Mother and Father)

I will briefly discuss the differences below. But if you wish to get a clearer picture of DNA testing, go to the following link and take the 3 courses offered. They discuss them more in detail:

Mitochondrial Testing

DNA, or “Deoxyribonucleic acid is a molecule composed of two polynucleotide chains that coil around each other to form a double helix carrying genetic instructions for the development, functioning, growth, and reproduction of all known organisms” according to Wikipedia.

There are two main types of DNA carriers, those in the cell nucleus and those outside of the nucleus.

Those outside of the nucleus are carried in Mitochondria. Wikipedia explains that “The mitochondrion is a double membrane-bound organelle found in most eukaryotic organisms.” Mitochondria turn the energy from food into energy for the cell. There are several thousand mitochondria in each cell.

Mitochondria is inherited from the Mother. Male Mitochondria is discarded. Mitochondria genes only change very slightly over time, such as 4 generations. This makes it excellent for testing direct-line Maternal relationships. In other words, if you are a female and you want to find matches with direct-line FEMALES back in time, with no intervening males, this test will be far better than others to accomplish that objective.

Y-chromosome Testing

Y-chromosome testing is the counterpart to Mitochondrial testing. It and Autosomal DNA (discussed below) are derived from Nuclear DNA. Y-chromosome testing does the same thing for direct line MALES that mitochondrial testing does for females. If you are a male and want to prove that your direct line ancestor, with no intervening females, is related to you, you should try Y-chromosome testing.

The reason is that males have an X and a Y chromosome, but females have two X chromosomes and cannot pass down a Y chromosome because they don’t have one. (X and Y chromosomes are called Allosomes, which are sex-determining chromosomes.) So if the Y-chromosome is very similar to another male’s Y-chromosome, it is likely that they are biologically related. Y-chromosomes never get modified by recombinations, but recombinations do occur in Autosomal DNA, as seen below.

This makes it excellent for testing for patrilineal males.

Autosomal DNA Testing

Human genetics is pretty awesome. It not only tracks direct line female and direct line male biological relationships, but also tracks combinations of relationships, however not as effectively. It does this through recombinations.

Autosomal DNA, like Y-DNA, comes from the nucleus of a cell. Twenty-two of the 23 pairs of chromosomes an individual human gets are Autosomal chromosomes, meaning they do not determine the individuals sex. The 23rd pair does determine sex, having the well-known X and Y chromosomes, and are Allosomal.

The way Autosomal DNA works is for each of the 22 pairs of Autosomal chromosomes a child gets, the father contributes 1, and the mother also contributes 1. So 50% of his or her DNA comes from the Father and 50% from the Mother.

The implication of this is that each generation back in time, using the 50% rule, would mean that the child will inherit 50% from each parent, on average 25% from each Grandparent, and on average 12.5% from each Great Grandparents, etc. The problem is that the further back in time you go, the less DNA can be effectively matched back to a specific individual. If you go back over 5 generations, it gets less and less probable that you can find an exact match in your known relatives.

An additional complication is that although you will receive 50% of your father’s DNA, there is no guarantee that the DNA he gives you is exactly 50% of what he had from his father and 50% from his mother. He may give you a greater amount from his father than from his mother, as long as what he gives you is 50%. On average, you can get 25% from each Grandparent, but it can vary. Even further back in time, an ancestor can drop out completely from contributing to your Autosomal DNA.

X DNA Testing

X DNA, like Y DNA, is Allosomal (it determines the sex of an individual) and is from the cells nucleus.

Males get one X chromosome from their Mothers, but none from their Fathers.

Females get one X chromosome from their Mother and one X chromosome from their Father.

For Females, one of the X chromosomes comes from her Mother, and the other comes from her Father’s Mother since her Father could only have gotten it from his Mother, the Grandmother.

The implication is that Males lose X DNA faster than Females going back in time. And remember that there is no guarantee that the percent inherited is evenly distributed between the Grandparents that do contribute.

X DNA testing is normally included when doing Autosomal DNA testing.

What test to use?

So what test should you take?

It depends.

If you want to answer a question on your matrilineal lines, use the Mitochondrial test.

If you want to answer a question on your patrilineal lines, use the Y-chromosome test

If you want to answer a question on a relative within 5 generations of you ,use the Autosomal test.

And remember that you may not even be able to get the results from your personal DNA, as in the case of a female wanting to get information on her direct male line, so you may need to get your male relatives to take the test for you in that case.

Good luck! I hope this was informative. The RootsTech course on DNA basics certainly was for me!

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