Hello Carpenter Cousins,
Recently two questions were asked regarding loss of matching cousins while using atDNA
(autosomal DNA) tests like Family Finder and the Ancestry DNA Test.
These are the questions:
1) I have a verified second Carpenter cousin on my genealogy that does not have a genetic
match with me on Ancestry and neither on
GEDMATCH.com. Any idea why?
2) The Lost Cousins Newsletter said something along the lines of occasionally a person
does not inherit the atDNA of an ancestor so there will be no 'cousin' matches
from that person. Does that mean that you will not have matches from that ancestor's
ancestors either?
The short answer is yes to 2). The lost segments can never be recovered via atDNA testing
to those who are related to you.
For both questions (1) & 2) ) the he longer answer involves understanding what is
inherited with atDNA over the 5 or 6 effective generations into the past.
The key in atDNA testing, from any DNA testing company, is the shared CentiMorgan (cMs)
segments. The size of the shared cM segment is indicative of the generation it is
inherited from.
This means you get less and less atDNA from each generation to compare to. You never get
more, you get one half (1/2) less from each generation back in time.
And for shared CentiMorgans (cMs) comparison, please see:
https://isogg.org/wiki/Autosomal_DNA_statistics#Distribution_of_genealogi...
You own your atDNA at 100%, with you being Generation 0. Each generation back in time,
that percentage is cut in half. You get for all intents and purposes 50% from each parent
(Gen. 1). Then 25% from grand parents (gps) (Gen. 2), 12.5% from the great (g) gps (Gen.
3), 6.25% from gg gps (Gen. 4), ggg gps 3.125% (Gen 5), 1.5625% from gggg gps (Gen. 5)
then .78125% from your ggggg gps (Gen. 6)
When you get to the 1% or less level with atDNA, you can get more random matches (called
identical by state) than real ones. This is where
GEDMatch.com comes in handy since it can
better track those tiny cMs segments for you.
In summary, you only get a fraction of ancestral atDNA, and odds are it will not be the
same, but increasingly smaller cMs segments that are shared with your cousins. Once you
get into that 1% or less level of shared cMs it means you are not seeing about 99% of that
generation. Conversely with your parents you are not seeing about 50% of each. The Lost
Cousins Newsletter is correct that the father back in time (generations) you will recover
or see less atDNA segments.
A helpful hint is to test the oldest generations related to you first. Because once they
are gone, much genetic atDNA data is lost for good.
For more information on the probabilities of cousin loss, please see:
https://isogg.org/wiki/Cousin_statistics#Theoretical_probabilities
In general, atDNA has an effective range of about 5-6 generations into your past with
increasingly loss of matching cousins because they have different shared cM segments.
Both mtDNA (mitochondrial DNA) and Y-DNA (Y-Chromosomal DNA) do not have this short range
problem. They are much more stable in their inheritance from their maternal and paternal
sides respectively. And Y-DNA testing is excellent for surname studies!
As a reminder the excellent sale prices and upgrades (especially for Y-DNA tests!) end at
the end of the year with
FTDNA.com.
I wish everyone a Merry Christmas and a Happy New Year!
John R. Carpenter
La Mesa, CA USA
Carpenter Cousins Project - Our main support page!
https://carpentercousins.com