DNA
and Your Tree
DNA in genealogy is a very new concept for me.
The relationship between cousins (which I struggle with) can be very important
to DNA matches simply because they can connect you to distant ancestors for
several generations. As a result, I have struggled with this post and after
considering just passing over it and starting a new post, I decided to “power
through” and create the post as best I can. The first step was to understand
cousins a little better with a “cousin calculator” which I have included at the
end of this post. [1] I also want to say at this point that this post is based
on autosomal testing which pulls from both parents rather than one or the other.
While there are plenty of records out there, the
accuracy completely depends on someone putting the information into that record
and how that record is read and understood. All these records can prove
or disprove family stories and legends and DNA can be an excellent companion to
these records. Just remember that while the DNA might prove you are related to
a specific person, it doesn’t necessarily mean you are automatically related to
that match's entire tree. By understanding the degrees of cousins, you can get
an idea of where to look in a family tree for your match and see how are
related to them.
Just as important when comparing DNA matches is
whether or not the trees being compared are sourced well, whether the sources
are correct, whether there are any sources or a tree at all. There is a way
around this. Understand your DNA information. Learn what the numbers mean and
how they indicate what the relationship is. Most DNA matching sites have names
attached to your DNA matches. Sometimes if it is enough of a real name, you
only need to use DNA numbers as confirmation. If there is a less than complete
name or a nickname, you may be able to figure out the relationship they share
with you using the DNA. As I said before, DNA is a great companion for records
and I am not suggesting that you rely on only DNA as a source for you family
tree.
Most autosomal tests use percentages and centimorgans
to determine how closely your match is related to you. Percentages are pretty self explanatory. For example, you are 100% you. Your parents
will be a 50% match because you carry half the DNA of each parent. Your
grandparents would be a 25% match to you and a 50% match to your parents. As
you can see the percentage match halves itself in each generation.
Centimorgans or
cMs for short also measure how close or distant a match is related. The number of cMs shared indicate the degree by which each DNA match is related.. A child’s cMs are made up of one half of each parent’s
cMs and one quarter of their grandparents cMs. The cMs halve themselves over
each generation much like the percentages do but with a large range of specific
numbers. By this I mean that the cMs may not be exactly halved or quartered and
there may be more or less cMs depending on what was passed down to each match genetically. On average a person will carry approximately 7400 cMs. I have
included a link that explains cMs in more depth as well as containing a
downloadable chart. [2]
Both percentages and cMs go through the ancestral
line and the descendant line of your tree and halve themselves in each
generation. In the same way your parents carry 50% of your DNA, your children
will carry 50% of your DNA, grandchildren like grandparents will carry 25% and
on down the line.
Hope you find these links useful and as always,
Happy Hunting!
Roni
