For Genetic Genealogy, which is the application of DNA testing to genealogy research, three types of DNA can provide information useful in conjunction with genealogy research. These types are the Y chromosome (Y-DNA), Mitochondrial (mtDNA) and autosomal (auDNA).

y-DNA - The Y-chromosome only exists in males, so is used for tracing male lines.

Mitochondrial DNA (mtDNA), is passed only in the egg outside the cell nucleus, so comes from your Mother and is useful for tracing female lines.

Autosomes are all chromosomes other than the X and Y. They can be used to link you to cousins on both parents side.

Within the non-coding (or Junk) DNA regions (regions which are not part of genes. 95% or more of the DNA) are certain known locations (loci) where a short segment of DNA (2-5 base-pairs) will stutter, repeating itself a number of times. This is known as a Short Tandem Repeat (STR). There are over 100 of these STRs called markers. They are given DNA Y-chromosome Segment (DYS) numbers to identify them. The number of repeats (Allele value) changes (mutates) over time. Testing involves counting the number of repeats for a group of these Testing labs typically use 12, 25, 37 or 67 marker tests to do for genealogy. The 25 marker test it the most common. These STRs have a couple of properties that make them attractive for genealogy.

  • The relative mutation rate for a STR is extremely slow (once every 250-500 generations), so most family members will have the same values. But they change enough so that people who do not share a common ancestor in their male line in the last several thousand years will have different values.

    The mutation rate varies among markers and recent studies have show that they also vary by family.

  • The number of repeats is inherited and is easily detectable. The targeted DNA fragment (marker) is amplified by polymerase chain reaction (PCR) and the number of motifs (repeats) of the target STR can be easily determined by gel electrophoresis.

mtDNA testing looks for single nucleotide (base-pair) polymorphisms (SNPs) in certain regions.

Testing:
There are several places where you can get your DNA tested.
The most popular is Family Tree DNA (FamilyTreeDNA.com)
Others are:
23andMe - Genetic Testing for Ancestry; DNA Test
DNA Tests for Ethnicity & Genealogical DNA testing at AncestryDNA
OxfordAncestors.com
See: Genealogical DNA Testing at (dna.reinyday.com) for others.

DNA Overview:

The rungs of the double helix DNA molecule are what vary from one person to another. They are made up of pairs of four bases, Guanine (green) always pairs with cytosine (red) and thymine (yellow) always pairs with adenine (blue). The order of these bases is called the DNA sequence.
You can write the sequence by listing the bases on either side.
A STR has pattern of 2-5 bases that repeats. DYS # 393 has the following repeat:
(GATA)(GATA)(GATA)(GATA)(GATA)(GATA)(GATA) ...
70% of the population has 13 repeats, 12% have 12, 12% have 14, the rest having 10, 11, 15 or 16 repeats.

A sample Haplotype from a 25 marker test:
DYS # for marker 3 3 1 3 3 3 4 3 4 3 3 3 4 4 4 4 4 4 4 4 4 4 4 4 4
9 9 9 9 8 8 2 8 3 8 9 8 5 5 5 5 5 4 3 4 4 6 6 6 6
3 0   1 5 5 6 8 9 9 2 9 8 9 9 5 4 7 7 8 9 4 4 4 4
        a b       i   ii   a b             a b c d
allele value (# of repeats) 14 23 15 11 11 14 12 12 14 13 14 29 18  8  9 11 11 25 15 19 28 14 15 17 17
Red DYS #s - Higher rate of mutation.

Anthropologists break down the Y-chromosome into branches called Haplogroups or clades, which distinguish major branches of Homo Sapiens. Haplogroup R1b1 is the most common haplogroup in European populations. It is believed to have expanded throughout Europe as humans re-colonized after the last glacial maximum 10-12 thousand years ago.

Migration charts show how verious groups migrated out of Africa.

Click to enarge.

See: Y-Chromosome Nomenclature System at U. Arizona for a report by the Y-Chromosome Consortium (YCC) where they say:
"The Y chromosome contains the largest non-recombining block in the human genome. By virtue of its many polymorphisms it is now the most informative haplotyping system, with applications in evolutionary studies, forensics, medical genetics, and genealogical reconstruction. ."

An article "DNA testing for Genealogy" at GenUKi.org.uk says:
"Whilst its benefits to genealogy may not be immediately obvious, there is growing interest in 'SNP' testing. Put simply, an SNP (single nucleotide polymorphism) is a rarer kind of mutation than the STR-based events that we normally test. They are the markers that divide up the human race's DNA tree at the high level and previously have been restricted to mutations which happen thousands of years ago. However in the early months of 2006 some very rapid progress has been made in the discovery of new more recent SNPs that are helping to bridge the gap from thousands down to hundreds of years. The most exciting of these is the so-called 'Ui Neill' or 'Niall of the Nine Hostages' marker. Led by Ethnoancestry, this drive to unearth young SNPs could be the second revolution in genealogical DNA testing and will be of particular interest to those connected with the Scottish and Irish clans who have deep pedigrees stemming from the kingdom of Dal Riata."

Terms:

Allele - The number of repeats of a sequence in a marker
DYS - DNA Y-chromosome Segment - See marker
haplotype - A string of allelle values for different markers
Haplogroups - Identifies the person's major population group and
   provides information about the ancient origin.
   R1b1 is the most common haplogroup in European populations.
Locus - Pysical locaation of a marker
marker - Repeated base-pair sequences at specific locations along the
Y chromosome. They are given DYS numbers to distinguish them.
non-coding DNA - DNA (sometimes called junk or filler DNA) which does not  contain
  instructions for making proteins (or other cell products such as noncoding RNAs)
  This accounts for 95-98% of the DNA
SNP - single nucleotide polymorphism - A change in your Y-DNA sequence at a
    location other than those in the 12, 25, 37, and 67 marker tests.
    SNPS are unique to specific haplogroups so SNP tests such as the Backbone
    and Deep SNP tests are used to identify haplogroups and their subclades
    respectively.
STR - Short Tandem Repeat - Short markers with 8-36 repeats of 2-5 base-pair
   sequences (DNA codes).
   These sequences are sometimes referred to as genes but they are
   not the same as the genes we think, which are much longer and used
   in coding for creating proteins determining amongst other things
   physical characteristics.
TMRCA - Time to the Most Recent Common Ancestor.
Y-STR - STR's on the Y-chromosome
Average of 1.3% nonpaternity events per generation
Rate of mutation = .002-.003 per marker. In other words,
we could expect any marker to mutate once in 300-500 generations. 
See:
The Glossary at FamilyTreeDNA
Genetic/Genomic Jargon at NewEnglandAncestors.org

Books:
"Trace Your Roots with DNA: Use Your DNA to Complete Your Family Tree:", Megan Smolenyak, Ann Turner
Adam's Curse, Bryan Sykes
Book List at FamilyTreeDNA

Links:
Genetic Drift
Molecular Biology has more about DNA and genes
Family Tree DNA testing - Tutorial
DNA testing for Genealogy at GenUKi.org.uk
  DNA Newbie forum at Yahoo Groups
DNA 101 at BlairGenealogy
Basics of Genetic Genealogy & DNA Testing at the Heffernan DNA Project.
DNA Mutation Rates
International Society of Genetic Genealogy
Haplogroups
Frequency charts for allele values.
WorldFamilies.net Your Gateway to Genetic Genealogy
Lists of other web sites at Genetics, DNA & Family Health at Cyndi's List
DNA Newbie forum Yahoo Groups
Sikes / Sykes DNA Project
Alvin Sikes Family DNA results
Sikes Surname Origins


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last updated 10 Aug 2007