This is the second in a short series of e-mails with some basic
information project members and those considering Genetic Genealogy
should have.
The information shown below is intended to give a brief explanation of
genetic genealogy as it is today. More information on the subject is
available on the web, in periodicals and books. Several links to
additional sources of information are provided at the end of this
e-mail.
Genetic (DNA) Genealogy - Paternal line genetic genealogy 'targets the
male-specific portion of the human genome, the non-recombining portion
of the Y chromosome or NRY'*. 'Two classes of NRY markers are short
tandem repeats (Y-STRs) and single nucleotide polymorphism (Y-SNPs)*'.
'The combination of alleles at multiple Y-STRs on a single Y
chromosome defines a Y-STR haplotype, whereas the combination of
alleles at multiple SNPs defines a NRY Haplogroup. An allele is
specific genetic information or variation within a chromosome,
generally referring to a specific location on a chromosome'*. In Y-STR
testing, which is what we use for paternal line pedigree
identification, the allele count is the specific number of times a
combination of the four sugar molecules that make up DNA are repeated
at a specific location, called a marker or locus, on the Y chromosome.
YSNP testing reveals changes in the Y Chromosome that occur more
gradually than for YSTRs. YSNP testing is used in anthropological
research to identify likely common ancestry between individuals within
hundreds of generations.
* taken from '2000-IJ-CX-K006 Cumulative Technical Report ', Michael
Hammer and Alan J. Redd, January 2006
Scientific researchers have identified specific locations on the Y
chromosome that can be reliably identified through chemical analysis.
For genealogy, we evaluate only markers that are known to be 'junk',
that is, they have no effect on our daily lives and do not have a known
function in determining a person's medical condition or personal
characteristics. Approximately 90% of our DNA is classified as 'junk'.
So, you can have confidence that you are not revealing anything about
yourself, other than your lineage, when you share your YDNA results.
Lineage can only be determined by comparison with others, the allele
count at the markers used for genetic genealogy has no meaning by
itself. The markers selected are also known to be very stable during
chromosome replication. Studies show that the allele count at any of
the specific YSTR markers that we use for genealogy changes about once
in 500 generations, though a change in the allele count, a mutation,
can occur during any Y chromosome replication during spermatozoa
development. Some markers appear to mutate slightly more or less
frequently, this difference in mutation rates is used to separate out
probable changes in more recent generations from those that likely
occurred many generations ago. Within a population of several males
sharing descent from a common ancestor, the Y-STR markers mutate the
allele count on average by one or two at one or two markers within 5 or
more generations. This slow mutation rate allows us to infer a high or
low probability of a recent common paternal ancestor within a
genealogically relevant time period.
The probability of men with common haplotypes sharing a recent common
ancestor increases in accuracy with an increase in the number of
markers in a haplotype. Sharing a 25 marker haplotype with another man
who shares your surname, or a derivative or phonetically similar
surname, is a very strong indication of a common paternal ancestor
within a genealogically meaningful time, say the last 10 generations.
Two individuals sharing a 37 marker haplotype have a 90% probability of
sharing a common ancestor within five generations. Haplotypes with 12
or fewer markers can only indicate common ancestry within 25 or more
generations. Usually, any two haplotypes that vary at more than four
markers do not share a common ancestor within 10 or more generations.
Two individuals with common surnames and exact haplotypes may still not
share a common recent paternal ancestor, the probability of this is
quite small however and has seldom been observed in DNA genealogy
studies.
Surname studies are used to improve the odds of a common DNA haplotype
revealing common recent paternal ancestry since males traditionally
have the surname of their father. Prior to the 1800's literacy was not
common among the general population however, so allowance must be made
for phonetic variations. Even after 1800 surname changes occurred for
many reasons, so traditional genealogical proof is required to
establish near certainty of common ancestry. DNA testing can reveal
where a recent common paternal ancestor is not likely or even
biologically not possible.
See
http://www.familytreedna.com/faq2.html#table1
Large DNA population studies consistently see 3 to 4% of haplotypes
reveal results that are not consistent with the documented or suspected
paternal ancestor. Non DNA matches within known familial relationships
have been reported to occur at this rate in many father - son studies,
genetic genealogy studies with many descendants of a known paternal
ancestor or within a regional population group that was been isolated
for many generations, as well as in larger population forensic studies
like the one referenced above. A non DNA match can indicate
miss-identity of the paternal line, adoption, unknown family history,
especially in earlier generations where mortality was greater than
today, or an extra marital event. This is genetic descent only, no
inference can be made about a specific person being raised by or having
a familial relationship with a specific family or group based on DNA
results.
Haplogroup definition - Scientists studying DNA have established
several large population groups with common YSTR allele counts, called
Haplogroups. DNA Haplogroup identification is being used today to study
population expansion through human history. Haplogroups are designated
by a letter of the alphabet, A, B, C and so forth. Each Haplogroup
roughly corresponds to a major population group descended from some
ancient migration of humans. Haplogroups tend to be strongest in
particular geographic regions such as Europe, Asia, Africa, and so
forth. Haplogroups are further broken down into subhaplogroups, which
break these large population categories down into smaller groups
sharing a more recent common paternal ancestor. The Phylogenetic tree
is used to show the relationship between Major Haplogroups and also the
sub haplogroups within a major Haplogroup. Haplogroups identify ancient
paternal affiliation. Many family history researchers find this
information as interesting as a near term genealogy connection.
Two individuals who share identical allele counts at two or more YSTR
or YSNP markers establish a Haplogroup. As with a haplotype, the
larger the number of markers in a Haplogroup, the more meaningful the
result. Several people descended from a common ancestor can establish
a DNA Haplogroup for that ancestor. A common ancestor who lived 10,000
or more years ago would probably have a large number of descendants
alive today. These descendants would of course have a number of YSTR
mutations from that common ancestor, but the haplotypes would still
cluster around a mean allele count value at each marker, called a modal
value. Modal values at several markers establish a Modal Haplogroup.
Haplogroup identification using single nucleotide polymorphisms, SNP's,
is more reliable. The YSNP Haplogroup of an individual living today
has a very low probability of having changed from a paternal ancestor
living 10,000 years ago. While Haplogroup identification does not
directly contribute to genealogy, two people can not have different
Haplogroup affiliation and still share a common paternal ancestor
within thousands of years. Thus YSNP allele variations can be used to
show there is no recent common ancestor even in the rare case where two
individuals share a multiple YSTR marker haplotype with each other,
which is useful in genealogical DNA studies where common YSTR
haplotypes occur.
YSNP Haplogroups correlate with YSTR Haplogroup modals, so once a YSTR
haplogroup modal is correlated with a Haplogroup established from SNP
testing, comparison of other YSTR haplotypes with that modal can
establish the probability of the Haplogroup affiliation. SNP testing
is required to eliminate the possibility of misidentifying the
Haplogroup however. Some YSTR haplotypes have allele counts that are
not close to the modal and are equally common to two or more YSTR
defined Haplogroups, only SNP testing can be used to verify the
haplogroup affiliation. A prime example of this are haplogroups R and
Q, which are adjacent to each other on the phylogenetic tree.
Haplogroup R is strongest in western Europe, while Haplogroup Q is
strongest in north eastern Asia. Yet many YSTR R1b Haplotypes have
allele counts that have more in common with Haplogroup Q than with
Haplogroup R and are occasionally misidentified as Q. This occurs
because of the more frequent mutations within YSTR markers and can be
resolved with slow mutating YSNP markers. YSNP testing is still in the
early stages of development and changes in assignment of
sub-haplogroups within the major Haplogroup categories, the
Phylogenetic tree, continue.
Haplogroup by SNP affiliation:
http://www.familytreedna.com/haplotree.html
The focus in the Carr Surname DNA Genealogy Project is on YDNA testing,
but mtDNA testing and autosomal DNA testing are also available for
maternal line ancestral identification and general ancestral
identification respectively. mtDNA testing can be used to establish
common maternal line ancestry, or unrelatedness. mtDNA passes from a
mother to her children and mutates very slowly, on the order of
thousands of years. So all the female descendants of a woman who lived
10,000 years ago will likely still share her mtDNA, which is likely a
large number of woman alive today. Since women do not traditionally
keep a common surname from generation to generation, surname studies
are not useful for maternal line genealogical research. Regional
studies that include known locations where a maternal line ancestor
lived are more useful for maternal line genealogical research. As with
YDNA, standard genealogical information is required to confirm
relatedness. Autosomal DNA is being used to infer cultural affiliation
or to identify which parts of the world your ancestors came from. The
inferred results from autosomal DNA testing have been questionable and
still need scientific development. Anyone wishing to be a DNA pioneer
may consider this form of DNA testing and contribute to the development
of autosomal DNA anthropology.
Links:
Explanation of Genetic Genealogy testing, this subject is also covered
on most of the DNA test company sites and many DNA surname project
sites:
The Blair DNA project:
http://blairgenealogy.com/dna/dna101.html (link
ends in .html)
Charles Kerchner's primer:
http://www.kerchner.com/anonftp/pub/introg&g.htm (link ends in .htm)
http://smgf.org/about.html
http://www.isogg.org/
http://www.dnaheritage.com/masterclass.asp
http://www.relativegenetics.com/relativegenetics/genetic_genealogy.htm
(link ends in .htm)
http://www.relativegenetics.com/relativegenetics/dna_movie.htm (link
ends in .htm)
http://www.ethnoancestry.com/info.html
Contact me anytime,
John Carr
Carr DNA Genealogy Project websites
Linking Carr/Kerr/Karr/Corr/Kear families around the world through
their genetic record
http://freepages.genealogy.rootsweb.com/~carrfamilydna/
http://www.carr-genealogy.com/DNA/.html