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What are centiMorgans, and how did they get in my DNA?

Updated: Jan 15, 2020

The popularity of DNA testing has surged in the past few years, and companies such as AncestryDNA, 23andMe and Family Tree DNA are reaping the benefits.

In 2017, Ancestry alone went from a database of just over 3 million testers in January to almost 7 million in its database by December, according to analyst estimates. With an aggressive marketing campaign and efforts to make their test more genealogy friendly, 23andMe comes in at a not-so-close second, with about 3 million testers. FamilyTree remains stuck below 1 million, even though the company offers a good product, as well.

Newcomers, such as MyHeritage and LivingDNA, also have not yet individually topped the million-test mark, but they are growing.

But once the results come in and people see what percentage of European, Asian or African lies in their genetic past, many testers lose interest because they are unaware of the power of DNA as a tool for genealogical research.

DNA can help break down "brick walls" – those family lines that just seem to end with no trace beyond that one great-great-great-grandparent.

Even more importantly, DNA is helping adoptees, foundlings and others with unknown parentage discover their biological relatives every single day. In thousands of cases, it's the only tool available to adoptees where their original birth records are sealed.

Just imagine.

You could be a 70-year-old man on his death bed and, if you live in New York State, be denied, by antiquated and cruel state laws, to see your own birth records – to know the truth of who you really are and where you came from. DNA testing has proved stronger than any state laws sealing birth records, because – as a science – it does not lie and cannot be manipulated. Your DNA is the one thing that truly belongs to you, and because you inherited it from your parents and their parents, it is a link that cannot be broken.

So, you've tested and you know now that you should have been wearing the kilt instead of the lederhosen, as one commercial would suggest.

What to do know? What does it mean that you are related to all of these people whose names you've never seen or heard before? Surely, that can't be right.

But it is.

It might seem impossible to the beginner, but by pairing your DNA results with traditional genealogical research methods, you can determine from just a few clues how you match that cousin.

The Basics

Unless you are an identical twin or triplet, everyone inherits different pieces of DNA from their parents through a process called recombination.

Every egg in a woman's ovaries carries it's own recombined DNA, and every sperm a male produces also carries recombined DNA from the father.

Again, unless you are an identical sibling, we all inherit exactly 50 percent of our DNA from each parent. But the 50 percent I inherited from Mom and Dad is different from that inherited by my older sisters.

This can be seen in something as basic as the ethnicity estimates. Mine breaks down to 32 percent Europe West, 27 percent Great Britain (3 percent Ireland/Scotland/Wales) and 24 percent Scandinavia. My middle sister's results show 41 percent Great Britain (16 percent Ireland/Scotland/Wales), 26 percent Europe West and just 8 percent Scandinavia. My oldest sister's results are 42 percent Great Britain (1 percent Ireland/Scotland/Wales), 42 percent Europe West, 9 percent Scandinavia.

We are full siblings – meaning we have the same father and mother. And yet, I'm the only one who shows a percentage of European Jewish. Because it was such a small amount, it could have been an error in the algorithm the company uses for these estimates, but I discovered recently that one of our 16 great-great-grandparents from Germany was Jewish.

Amazing, isn't it?

So, if you have tested and you get an email from someone you match asking for information, please respond – even if you don't have any information to give them. But, if you have done research, make your tree public so that others can see how you connect.

There is so much more – and I haven't even told you what centiMorgans are!

I guess you'll have come back to read my next post.

Questions about DNA or genealogy, in general? Contact Phyllis by email, or, try the new live chat feature on this website!

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