Father’s day is always an occasion for the DNA testing companies to offer discounts on their kits and this year is no different. Give Dad a DNA kit is the message. Why should you? Well his autosomal DNA might find cousins you had lost track of, discover ethnicity you were curious about, or solve an unknown parent mystery. After all, he is one generation closer to your ancestors. I tested my late father long ago and am grateful to have that information. Click here for my evaluations of the different autosomal testing companies.
Dad and I in about 1953 (he was in the Air Force)
Only men have a Y chromosome and there are tests for just the Y. Those tests can give you information about your surname and your deep father line ancestry. Family Tree DNA is the place to test just the Y although both LivingDNA and 23andme will give you a high level Y haplogroup, plus there are tools to determine the haplogroup from an AncestryDNA or MyHeritage test (discussed at the end of this post).
If you know what a Y haplogroup is you can skip this paragraph … The 23rd pair of chromosomes is an XX for a woman and an XY for a man. The problem or benefit is that there is no second Y for that Y to recombine with. Thus unlike the other 22 chromosomes a man’s parents give him, the Y is unchanged from his Dad’s and his Dad’s and his Dad’s and so on, except for mutations. Those little changes accumulate over thousands of years and allow scientists to catalog the Y and trace the migration of mankind around the globe. Each set of Y mutations is assigned to a haplogroup, and subgroup, which can tell you where your ancestors came from thousands of years back. Here is the latest diagram from the
wikipedia article on Y
Y haplogroup world expansion – start at the big Y in Africa (A was the first haplogroup) -image from wikipedia by Maulucioni [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)]
There is a wonderful site at http://www.y-str.org with many good tools for Y DNA and autosomal DNA that run as programs on your PC plus a cool ISOGG Y tree add-on for the Chrome browser. My specific interest at the moment is figuring out which Y SNPs are already tested by 23andme so as not to test them again at FamilyTreeDNA since my Dad has kits at both places. I blogged about how to do that manually back in February, but now there is a program that will do that for you. However it took me a while to figure out how to do what I wanted from the instructions given, so I will do a step-by-step tutorial in this post in order to remember what I did.
First download your raw data from 23andme by going to the “Browse Raw Data” Page which is listed in the menu that appears under your name on the top right. Then on the raw data page click on “Download” in the second top bar on the right hand side. This takes you to a page with various warnings and requires that you reenter your password as well as the answer to your secret question before it starts the download.
Save the download file somewhere that makes sense for you. I have a folder called RawData in the folder DNA that I use. Once the raw data file is downloaded, you will need to unzip it before using it with the various tools. To unzip in windows all you need to do is open a file explorer window (a manila envelope is the icon) and then right click on the file name to get a little menu that includes “extract all” which is the one to click.
“My half-sister and I have been tested to confirm half-siblings. Is there any way to know which parent we share” – this is a rephrasing of a question posed by a woman on the DNA-ADOPTION mailing list at Yahoo. A discussion of the problems of mtDNA ensued. Because the mtDNA haplogroups go back thousands of years, a match is no guarantee of a recent ancestor like a mother. So that information can only rule out the maternal side if there is a mismatch. Deeper mtDNA can get closer but still this is not certain territory yet.
However since they are both female, the X chromosome can give a definitive answer because their father(s) would pass his only X chromosome unchanged to each of them. A man has one X and one Y chromosome and a woman has two X chromosomes. Whether the father passes an X or a Y to his child determines its sex, but since neither is recombined the child gets exactly the same X or Y chromosome as the dad has.
Since a girl has two X chromosomes, one is from her dad. Two sisters with the same dad will therefore ALWAYS match on the entire X chromosome since they have one complete X in common. If the mothers are related, then some of their X will be a full match as well. So let’s look at some X chromosome comparisons at GEDmatch:
This is what the two half sisters from the question look like. The blue indicates that there is a match, the colors above it whether on one chromosome (yellow) or both (green), while red is no match. A few small errors can creep in when processing DNA so an occasional little red line can be from an error. Click the read more once you have decided if they have the same mother or the same father.