About Autosomal DNA
Autosomal DNA represent the fastest-growing DNA tests for
genealogy As of July 2013, about 19% of Taylor Family Genes members
had purchased auDNA tests from FTDNA. This page presents a brief overview.
The term is often abbreviated "atDNA"; here, we'll use "auDNA".
- Tracks all family lines, not just direct paternal and maternal.
- Can identify cousins, out to the the fourth cousin or, sometimes, fifth
- Some users have reported genealogically significant matches beyond 5th cousins, but these
are not to be counted on.
- Limited as to number of generations
- Databases for matching are presently smaller than the sizes needed for
"blind testing" and of
either Y-DNA or mtDNA. (The databases are growing rapidly.)
- Complicated; requires advanced genetic knowledge.
- May require testing multiple family members to interpret matches with
Autosomal refers to the 22 chromosomes that are not gender-determining,
though some tests also include the X chromosome. We have two copies of each
chromosome, one from Mom and another from Dad
DNA is composed of pairs of four bases -- A (adenine), C (cytosine), G
(guanine) and T (thymine) -- AT, CG, etc. These are known as "base pairs" and are arranged in sequences along the chromosomes.
Base pairs are sometimes (incorrectly) referred to as SNPs,
but SNP means that more than one form is observed and this isn't
necessarily the case with base pairs; some exist in only one form.
reading the sequences, an identifying signature is determined for particular
segments. The identifying signatures are then searched across an entire
database of comparable reads and identical segments are reported as matches.
In general, longer identical segments indicate closer relationships and
shorter identical sequences indicate more distant or no relationships.
Estes' blog and
Autosomal DNA has little to no association with any surname. If your family is typical, each of
your ancestors in almost every generation had a different surname. For most
participants, Taylor will be only one of 32 or more surnames represented in
matches. Each genetic family will be unique to the individual participant.
Presently, Taylor Family Genes does not take an active role in autosomal
it is primarily an individual endeavor.
Project administration is not involved with your auDNA results or matches.
Nor, are project administrators especially skilled in interpreting the
complexities of AuDNA. If you have a question, however, we will attempt to
get an answer for you.
Humans have 23 pairs of (46) chromosomes contained within the nucleus of
each cell. One pair of chromosomes (XX or XY)
determines gender. The other 22 pairs are called "autosomes" and their
acid is autosomal DNA.
Note that the chromosomes are paired;
there are two Chr4s, two Chr10s, two Chr13s, etc.
Autosomal DNA governs most of our physical characteristics and bodily
functions. It determines the color of our eyes and hair and many other
things about us.
At conception, we receive one half-pair of each chromosome from our
mothers and the other half from our fathers, making a full pair of each.
So, we get roughly one-half our autosomal DNA from each parent. And each of them got one-half
from each of their parents. As the table below shows, this rapidly dilutes the DNA received from each
|auDNA from each ancestor
||Aunt/ Uncle, Half Sibling,
Double 1st Cousin
By the time we get to generation 11, the DNA from each ancestor is highly diluted
with the DNA from all the others. In general, it's estimated that beyond the
7th-generation ancestor (5th-great-grandparent) the
unique DNA we carry from each ancestor is almost undetectable.
But, dilution is not the end of the story. As the autosomes (and XX)
find each other and pair up, they swap genetic information with their partners in a process known as
recombination. Mom's copy of Chr1 will interact with Dad's copy and vice
versa, jumbling the inherited information.
Some information on one chromosome is over-written by information
from its mate. This means we may get a little more or less than half our
auDNA from one parent or the other.
The two halves of each pair look a little more like each other than they
did before. That results in an inheritance pattern like this:
Recombination is why full siblings other than identical twins are a little different from
Dr. Bruce Walsh used this analogy to explain auDNA inheritance:
- Take two pots of cooked spaghetti, one pot of red (tomato flavor) and one green (spinach
flavor). they can be small pots, you only need 23 strands of each color.
- Pour the pots out on a table together and chop them into random lengths with a cleaver.
- Mix well.
- Put half in one pot, the other half in another pot. One pot will have a
little more red, the other a little more green.
- For the next generation, cook two more pots of different colors. Repeat
steps two to four.
Dilution and recombination make auDNA matching complicated and limit how many generations it
can look back.
The three major players in auDNA testing (which facilitate matching) their advantages and disadvantages are
Family Tree DNA
- Sole focus is on genealogical uses
- No subscription fee; test cost covers ongoing services
- Names & contact info of matches provided
- Excellent customer service
- Larger international presence
- Partnership with NGS Geno 2.0 project promises to grow
- Increased possibility of coordinating with Y- & mtDNA
- Smaller database, ~100,000. (Appears to be growing rapidly)
- Largest database, >700,000.
- Reportedly, superior analytic tools.
- Major focus has been on health risks. Genealogy has been a secondary focus
(Has changed due to FDA regulation)
- Names of matches not provided
- Monthly subscription fee to maintain services
- Poor customer service
- Customers less likely to respond to queries following matches
- Sole focus is on genealogy
- Matches linked to family trees.
- Rapidly-growing database, >500,000
- Reported lack of transparency and data access
- Subscription fee
ISOGG's comparison, which covers -- in addition -- the NGS Geno 2.0
project and BritainsDNA Chromo2 test.
As with other types of DNA used in genetic genealogy, the process with
- Get a test and have results entered in a searchable database;
- Find matches -- those whose DNA is sufficiently similar as to indicate a
recent common ancestor;
- Communicate with the matching persons to identify common ancestor(s).
Note: At this time, the databases are relatively small for finding matches at random. The
largest, for example, represents less than 1/1,000th the population of the United States and
much less than 1/1,000,000th the world population. Users may need
to recruit their matches.
What is a "match"?
About 99.5% of our individual DNA is the same as almost everyone else in
the world. Therefore, auDNA matching focuses on the subtle differences in
the other one-half percent; it looks for people with whom you share more
A match consists of persons who have sufficiently long strands of
identical (or, half-identical) DNA. In general, the longer the identical strands, the closer the
However, identical strands can be classified as IBD or IBS:
- IBD = Identical by Descent: The type of match we're seeking.
Comparison of the two DNA results indicate a high probability of a
- IBS = Identical by State: A "false positive", short
lengths of DNA may be similar due to random chance and represent "background
noise" in the DNA signal.
In general, IBS matches tend to be on shorter sequences than IBD matches.
Phasing is the method for determining whether autosomal matches are on your mother's
side (phase) or your father's.
Technically, "Phasing is the task or process of
determining the parental source of a SNP's alleles." It usually
requires at least two sets of results from known relatives -- one on the
paternal side, one on the maternal.
Segments are typically measured in centiMorgans, abbreviated cM.
A match points to a contemporary (hopefully living) cousin who descends from an
ancestor you share with him or her. The number of such cousins grows at an
exponential rate as the number of generations of separation increases. At
the same time, the amount of shared DNA increases, also at an exponential
rate, decreasing the percentage that can be detected through matching. The
net effect is that the number of detectable cousins grows almost linearly.
Most of the cousins found via auDNA matches will be distant, 5th degree
or more. That's because their number grows faster with generations of
separation than the detection rate shrinks.
One intriguing feature of autosomal DNA testing is that it can estimate
your ancestral origins by place. The diagrams below depict the ancestral origins of
one member of Taylor Family Genes.
The image on the left shows the members to be "99% European"; the missing
1% probably represents the margin of error in the estimate. Note that there
are three centers of focus: British Isles, Scandinavia and Southern
Europe (Balkans to Iberian Peninsula) The image on the shows relative
- Scandinavia -- 43%;
- British Isles -- 29%; and
- Southern Europe -- 27%.
The biggest surprise for the member was the relative size of the
Scandinavian component, that it outweighed the British Isles component.
Autosomal DNA can not find all your cousins, for reasons state more fully at
You have a lot of cousins, "..190 third cousins, 940 fourth cousins and 4,700 fifth cousins, 23,000 six cousins and so on. For every degree of cousinship increase, we expect five times more cousins."
But, in order to match, you must share at least one DNA segment with them. The chances are less than you might think and decrease with each step.
("C" means cousin; "R" means once removed.)
The chances of sharing even a single DNA segment with a 5th cousin are
only 30% and with a 6th cousin only 10%. Similarly, you have only a 10%
chance of inheriting a DNA segment that your 4th-great-grandparent once had.
The above would hold even if technology could read the DNA completely
accurately. With the current state of the art, some errors are inevitable;
they become more frequent -- and computationally difficult to resolve -- as
the segments get smaller. (Segment-slicing is inherent in autosomal DNA