23 May 2013

All Mama's Children

So last post talked about the Y Chromosome test that can tell you more about your father's direct paternal line. What about mom? Is there something that mom gives her child that dad doesn't? One would assume that if the Y Chromosome worked for dad's line, that the X Chromosome would be mom's, right? I mean, a man has a Y and an X, and the X has to come from his mother.... so .... ya know... solution. Not really. Okay, so there are 23 chromosome pairs. And one pair is known as the sex chromosomes. That's an X and a Y for a boy and two X's for a girl. For those of you noodling this out as we go along, you may have spotted the problem. To get a girl, dad has to give an X too. And because of translocation, during meiosis (the creation of an egg) the girl's X chromosomes can swap genes. So while your mother only passes down one X, she may not get one that is 100% one parent or the other. So how do we find out more about our matrilineal line like we do our paternal?

There is one thing that mothers pass down that fathers do not. Mitochondria. What is it? Inside every cell are these energy producers known as mitochondria. They have their own DNA, which suggests that this organelle may have been a bacteria that evolved to live in our cells. The great thing about the mitochondria having it's own DNA is that it has specific mutations. And because a mother passes down her mitochondria (the father's sperm cells have them, but they are dissolved during fertilization of the egg), this is our best bet for knowing about our mother's direct maternal line. Now, there are exceptions to this rule. Very rarely a man will pass his mitochondria down rather than the woman. Because it does happen, there is some pushback on how accurate we can consider this test. However it's so rare that most people don't worry about it.

Just like "Y Chromosome Adam", there is a "Mitochondrial Eve". Eve lived approximately 200,000 years ago and is the MRCA (Most Common Recent Ancestor) of every living human (on their mother's side). As Eve had daughters, the mitochondria changed and mutated. The mutations are now used to know what branch of the family tree is yours and how you connect to humanity as a whole. MtDNA uses SNPs (Single Nucleotide Polymorphisms), so the results are considered more "ancient". The fact that mtDNA isn't as accurate for recent generations is used by detractors more than the whole "men can sometimes pass down their mtDNA instead of women" thing. But this one's a little harder to refute. I would like to point out that currently it's considered the most accurate matrilineal test we have AND that no test is really useful without real genealogical research to back it up. So don't neglect your documentation just because you take a DNA test!
A mother passes down her mtDNA to all children.
Because mothers pass down this DNA to all their children, sons and daughters can both take the mitochondrial DNA test (mtDNA). You can test to find out about your mother and her matrilineal line, but what if you want to know about her father's mother? Just like the Y Chromosome test, choosing a subject for testing is easiest when using a pedigree chart to help visualise. Above is the same chart we used for the YDNA test. This time, we're hoping to solve the identity of Mystery Mother. Again, the S/P indicates "sans progeny" and those children have died without producing a child to test. You could choose any of her sons or any of her daughters. You can choose any of the daughters' sons or daughters. But notice all of the sons' children are crossed out. The children of the sons will get the mtDNA of the spouse and therefore will not help us find Mystery Mother. So while a male can take this test, testing your brother to find out about your father's mother won't help you. I personally would love it if my father would test his mtDNA so we could know more about his mother's maternal line (another of my little brick walls). My brother is taking the National Geographic test and will have his mtDNA tested for our mother's maternal line, which will help us learn more about our great grandmother's mother (my current maternal brick wall).

So what companies will you be able to get the test from? Just like the Y Chromosome test, the big two are Family Tree DNA (Ftdna.com) and National Geographic. Family Tree DNA is having a sale right now for either introductory Y Chromosome or mtDNA testing for only $49. These are introductory, so they aren't really "useful" to your genealogical research. However, if you have an elderly relative you are worried will pass away before you can afford to get the more detailed tests, this is the perfect way to "save" their DNA for later. FTDNA stores their sample for retesting for years. And you don't have to buy both tests for your male relatives. You will be able to upgrade the Y Chromosome test to a combo test later without having to purchase the separate mtDNA test now. National Geographic is $200 whether you are male or female. Men will get the added bonus of Y Chromosome testing, but both men and women get mtDNA and autosomal testing. There are of course other sites and companies, but these are the most recognised.

An mtDNA test is just like the Y-Chromosome inasmuch as it only traces one direct line (in this case, your mother's mother's mother etc.)

The Caveats
1. This test is considered more accurate for your deep maternal ancestry rather than the recent stuff. It can help you find your mother, but only in conjunction with real research. Even the "Full Maternal DNA" test provided by Family Tree DNA can only get within 9 generations (while a Y Chromosome test at 111 markers can get as close as 4).

2. Because you may need to test another person, be ready to answer questions by doing a lot of research. Be able to tell that other person what company you are using. What the results may show. How they will participate (most tests require the subject not eat or drink before giving a sample). What the realistic turnaround time is. How you will use their results: Do you want to make them public so you can connect to living relatives or will you keep them private and are only satisfying your own curiosity. The more you know before you ask for their help, the more likely they will help.

3. The number of markers matters. An introductory mtDNA test from Family Tree DNA will only get you within the last 28 generations.

4. And more markers means more money. Even at the "high" prices, however, I'd like to point out how affordable DNA research has become in less than 20 years. We couldn't even dream of something like this a mere two decades ago. Be thankful that it costs as little as it does.

5. DNA test are non-refundable. Notice I used red, underlined and italicised bold-faced large font "non-refundable". If you don't like the results, tough tits. The labs aren't out to get you, that's your DNA.

So there you have it. An mtDNA test will get you your direct maternal line just like a Y Chromosome test will get you your direct paternal line. There's still the possibility of a surprise "hiccup" in your ancestry. We're all pretty sure of who our mother is. What if you were adopted and don't know it? What if you are one of those "switched at birth" babies? What if your "mother" is your aunt or grandmother who took you as their own because your mother was a teenager unable to care for you? Just like a non-paternity event (NPE), you have to be ready. And just like before, I can't tell you how to do that. If "family" means "biologically connected", then DO NOT TAKE A DNA TEST. Something this deeply personal requires self-possession, demands the ability to take yourself out of the situation, and insists on a rational mind over an emotional heart. If you aren't strong enough, the current of unbridled truth will take you under and drown you.
Only the brave need jump into this gene pool.

No comments:

Post a Comment