DNA is a complicated chemical topic, and I won't go into the topic in detail. I want to focus on DNA as an information topic--and DNA carries a wealth of information. We have learned to read the chains, and to understand more of its message.

Family history includes the art of researching records and stitching them together into stories of our ancestors. Family science involves the study of genetics, and includes exploration of a new kind of record--human DNA.

Tests offer us a new record about relationships, but the hype sometimes overpowers the hope. Family Science and Family History are colliding. It looks similar to the Invasion of the Computer People.

What's DNA?
If you uncoiled the DNA in a cell, it would be about three meters long. You couldn't see it; it's a lot smaller than a hair. In order to see it, you'd have to use a powerful microscope to enlarge it about 1000 times, and then read your way from the Lincoln Memorial all the way to the Capitol Building. If you didn't enlarge it, and you stretched out all of the DNA in all of your cells, it would reach to the sun and back. Did I say it was a lot of information?

The DNA itself is composed of “base pairs,” and the bases are called A, C, T, and G after the long chemical names of the four sugars used in DNA. If anyone thinks you're not sweet, tell them that you are made out of a lot of sugar. They will not be impressed, but they might leave you alone.

We have two kinds of cells. Germ cells are used in reproduction. All of the other cells are collectively called “somatic cells.” Women are born with all of the germ cells that they will ever have, known by the technical term of “eggs.” They must be less wasteful than men, who can create more germ cells to replace the ones they lose. (It's ironic that the way our bodies manage the information needed to procreate mirrors the stereotypical differences in people. How often do you hear a man say, “Honey, have you seen my blue shirt?”)

A cell has two kinds of DNA in it. The nucleus contains “nuclear DNA” which is used for cell division. The area of the cell outside the nucleus contains “mitochondrial DNA (mtDNA)” which is used to release energy in cells. Mitochondria are organelles in cells, and we'd dry up and blow away in a few minutes without them.

Okay, so you have two kinds of DNA, and they are organized into chromosomes (you have 46 of them), and the chromosomes contain the genes (you have about 30,000 of those). So genes are DNA. Forget anything else, but remember that.

How Do They Read It?
Let's start by saying that reading DNA is hard. The “record” itself is tiny, smaller than a hair. To test it, you need a lot of it. Enter Kary Mullis, who in 1983 invented a process called “PCR” that lets biologists copy DNA without knowing much chemistry. Mullis says, “You can create 100 billion copies in an afternoon.”

Genes are the parts of the DNA alphabet that are use to create proteins. But there are long stretches between the genes that don't make proteins, like highways between towns. We don't know what those parts are used for, and call them “junk DNA.” In these long stretches, just like driving through Kansas, things start to look the same. Literally, sequences of letters show up over and over. We call these “markers.” DNA tests consist of identifying your markers and comparing them to the markers of other people.

How Can It Help Me Learn about Relationships?
Here's the cool part. You get your mtDNA from your mother, and she got it from her mother, and so on. You have your great-great-grandmother's mtDNA, exactly, sugar for sugar, in every cell of your body (except for mutations, but let's ignore those for now). If you are a male, you have a “Y Chromosome” (Y DNA) and you got it from your father, and he got it from his father, and so on. If you get mtDNA or Y DNA tests you can prove inheritance, or relationship. DNA has replaced blood in the determination of “blood relationships.”

If we group a lot of tests together with surnames, we can perform “One Name Studies.” If you have a common surname, such as Davis, there are many Davises out there that are not related to you. How can you sort them out? By a One Name Study with a Y Test. Why a Y test? Because surnames, like Y chromosomes, are often passed from father to son in our culture.

But you can't get your whole family tree from a DNA test.

You Mean DNA Has Limits?
DNA tests offer a feature called a MRCA, for “most recent common ancestor.” This concept is based on some math and tests of two people's DNA. It can't tell you who your common ancestor is--it can only get within a few generations of the number of generations when you and the other person had a common ancestor.

Also, since Y chromosomes are copied exactly, a link might be your father, or it might be your uncle. Or your great-uncle. Or his grandfather. Unless the cells mutate, time doesn't pass on the Y chromosome at all. And that mutation, how often does that happen? The tests assume a steady rate of change, and work well for large groups. But mutations can happen at any time--and if you find three mutated markers it doesn't mean it took three times the average mutation rate to happen.

They can tell you what group of humans you are in, but they can't tell you the name of your great grandfather. They can't tell you how many generations, exactly, that you are descended from someone.

If you are thinking ahead, you realize that these tests also can't tell you anything about the six great-grandparents that weren't your father's father's father or your mother's mother's mother. With each preceding generation, DNA records a smaller and smaller part of your heritage.

There are many firms offering DNA tests, but my favorite is Family Tree DNA, because CEO Bennett Greenspan is an honest man who knows his stuff. He wants to tell people what they want to hear, but when the evidence says he can't, I can see that it hurts him. He has to tell them that they aren't related, or that the test won't work, or that the case isn't proven.

More Information
If you want to discuss your Family Science issues, please drop by the RootsWorks Forums at www.rootsworks.com/forums. Registration is free, and I'd be interested to know what kinds of issues you are facing. Additional information and links can be found at www.rootsworks.com/familyscience.

Beau Sharbrough is a product manager at Ancestry.com. His articles contain his own views and opinions and do not reflect any corporate policy or statement by the company. He lives in Provo, Utah, where he is trying to see all of the national parks. The RootsWorks series of articles focuses on genealogical applications for generic technologies. Please note that he cannot assist you with your individual computer and genealogy problems. Visit the RootsWorks website www.rootsworks.com for links to previous articles and Beau's lecture schedule (next stop: FGS conference in Austin, Texas, in September).

Copyright 2004, MyFamily.com.