DNA Testing Does NOT Replace Our Traditional Research

The ABCs of DNA –An Introduction to Genetic Genealogy
by Debra Smith Renard, Eureka! Genealogy, Louisville, Kentucky

Introduction

Proof is a fundamental concept in genealogy. To meet standards of credibility for our family history research, the first step in the Genealogical Proof Standard is a “reasonably exhaustive research for all evidence that might answer a genealogist’s question about an identity, relationship, event, or situation.” This step ensures we examine a wide range of high quality sources and minimizes the risk that undiscovered evidence will later overturn a too-hasty conclusion. DNA is a unique record, one we carry within us. DNA testing is the most accurate tool available, ~98%+, far more accurate than any other tool or source we use for our research.Be ready to accept surprising results. If you’re not, it’s better not to test!

•DNA testing does NOT replace our traditional research

•It is used in conjunction with a well-formed pedigree

•It can support or refute our previous conclusions.Sometimes it raises more questions.

•It’s best to start with a specific question & hypothesis

•Be ready to accept surprising results.If you’re not, it’s better not to test!

•Most useful when comparing your results with others, especially those in your extended family

DNA Basics

DNA is found in the nucleus of almost all our cells

•We inherit half of this nuclear DNA from each parent

•It’s a mixture of a portion of the DNA they inherited from each of their parents

•It is contained in 23 paired packages called chromosomes

•First 22 pairs are called autosomes; 23rd pair are the sex chromosomes that determine gender

•Females have two X chromosomes, males have an X chromosome and a Y chromosome

•You get one of each pair from mother, one from father

DNA is a very long, thin molecule

•Its structure is a double helix, like a twisted ladder; the rungs of the ladder are built from 4 possible chemical bases: Adenine, Cytosine, Guanine, Thymine (A, C, G, T)

•They come in pairs that fit together like puzzle pieces.

•A -> <- T C -> <- G (straight-edged letter to straight-edged letter, curved to curved)

•So we only need to know what’s on one side of a pair to know what’s on the other side

The Human Genome

•The human genome (all of one’s genetic material) has about 3 billion of these base pairs of DNA

•For any two humans, about 99.9% of their DNA is the same. So we differ on “just” a few million locations.

•Ways in which two people’s DNA differs and ways in which it matches determine degrees of relatedness

Another important kind of DNA

•Outside the cell nuclei are many structures called mitochondria,the “power plants” of cells

•They contain DNA in circular moleculeseach consisting of over 16,500 base pairs

•Circle is divided into 3 main regions - two hypervariable control regions: HVR1HVR2, and the Coding region.Majority of markersare in the coding region.

Kinds of DNA Tests

Currently three main types with variations:

Y-chromosome (Y-DNA) used for patrilineal (direct paternal) line
Mitochondrial DNA (mtDNA) used for matrilineal (direct maternal) line
Autosomal DNA (atDNA) tests for all ancestral lines, but useful for fewer generations back
X chromosome (X-DNA) is not a separate test, but atDNA results usually include data on this

All three types of tests provide variations of three things

Results based on specific chemical bases in your DNA
List of people in the company’s database you match
Ethno-geographical origins for the lines relevant to that test

Y-DNA

•Y-DNA is only found in males and is passed down the patrilineal line from father to son to son to son…

•Most of the time it undergoes no significant changes. But random mutations (changes due to errors in DNA copying)with no impact do occur and accumulate over time.

•Since Y-DNA is only passed from father to son, a particular Y-DNA haplotype (a collection of genetic values) is associated with a surname in many cultures.

•Males who are close patrilineal relatives will have same haplotype

•Y test results include a list of people you “match”

•Two kinds of Y-chromosome Testing

•Short Tandem Repeat (STR)

•A short series of base values is repeated a number of times at a particular location

•We don’t care what the actual base values are at a location as much as how many times the sequence is repeated there.The number can change over time and be passed on.

•STRs are identified by a “DYS” number, e.g., DYS393

•Total number of DYS marker values reported varies with level of test

•Possibly 12, 25, 37, 67 or 111 markers; 37 min for most genealogical purposes

•The closer two results match, the closer the genetic relationship

•Single Nucleotide Polymorphism (SNP) (Second kind of Y-chromosome test)

•A SNP is a genetic change in a particular nucleotide (base pair)

•Most common mutation in humans. On average, there’s about 1 SNP for every 300 nucleotides. Since we have 3 billion base pairs, that’s ~ 10 mil SNPs.

•These mutations are passed on to subsequent generations

•Use these to identify haplogroups designated with letters of the alphabet and the ancient paternal ancestry associated with them

•STR test (the other Y test) can only give an estimated haplogroup

•SNP testing is more precise and will result in a specific sub-clade, such as E1b1b1c1a or E-PF6751 (terminal SNP)

•Y Haplogroup Migration

•Starts from Africa, spreads to Europe & Asia, and finally to the Americas

•Progressive presence of SNPs in indigenous populations enables tracking of historic migrations

Mitochondrial DNA (mtDNA)

•mtDNA is passed from mothers to all their children, but only females pass it on

•Because of this inheritance pattern, it is an indicator of matrilineal (direct maternal) ancestry: mother’s mother’s mother’s mother…

•It changes even less than Y-DNA

•Random mutations do accumulate very slowly over time and are passed on

•Even distant relatives may be a close match, so least helpful test for genealogical purposes

•Three levels of mtDNA testing

•HVR1 – don’t do this one by itself any longer

•HVR1 & 2 together - still only tests ~7% of mtDNA sequence

•Full Mitochondrial Sequence (FMS)includes entire molecule – i.e., both HVR coding regions

•Test results are expressed as a list of all your differences when compared to a reference sequence

•Includes a list of people you match within a certain genetic distance

•If exactly match on FMS, you may have a common ancestor within a genealogically meaningful timeframe

•Mutations are passed on to subsequent generations

•Like Y-DNA, used to id haplogroups with letters and associated ancient maternal ancestry

•The lettering system used has no connection to that of the Y-DNA haplotree

•Mitochondrial Haplogroup Migration

•Again, starts from Africa, spreads to Europe & Asia, and finally to the Americas

•Progressive presence of SNPs in indigenous populations enables tracking of historic migrations

Autosomal DNA (atDNA)

•atDNA is found in the 22 pairs of autosomes

•Newest type of testing, evaluates over 700,000 SNPs

•Inherited from all your ancestral lines through both parents

•Since we get one of each chromosome pair from each parent, get 50% of our atDNA from each

•They, likewise, inherited 50% from each of their parents; therefore, we get about 25% of our atDNA from each grandparent, about 12.5% from each great-grandparent, etc.

•The % inherited is halved with every generation back.That means ancestors gradually fall off our autosomal genetic family tree. Usefulness of atDNA testing is limited past 5 or so generations.

•atDNA Testing Results

•Get a very large file with actual values at 700k+ markers, along with list of people you “match”

•Some testing companies and third parties provide tools to focus on the significant parts. For example,they showlocationsof chromosomesegments on which someone else matches us.

•The longer the segment on which someone matches us, and the more total DNA we share, the more likely we are closely related

•Chart of average % DNA shared with various relationships is at

•E.g., siblings 50%, grandparent 25%, 1st cousin 12.5%, 2nd cousin 3.125%, etc.

•NOTE: “Half” relationships = half the shared DNA, “Double” ~ 2x

•It’s really a range: 1C 7.31-13.8%, 2C 2.85-5.04%, 3C 0.3-2.0%, 4C 0.07-0.5% (23andMe)

Testing Companies

AncestryDNA

•atDNA only

•No chromosome segment analysis, but have total DNA shared with match and # of segments. Look for “i”.

•Extensive presence of family trees

•Some of newest features: Shared Ancestor Hints, DNA Circles, Shared Matches, Genetic Communities

•Can download raw data; can also import to FamilyTreeDNA

FamilyTreeDNA

•atDNA (Family Finder), Y-DNA STR at various marker levels, & mtDNA HVR 1&2 or FMS

•Also tests for specific Y SNPs

•Excellent tools for autosomal analysis: In Common With (and Not…), chromosome browser, matrix

•Access to many projects, especially those associated with Y test results

23andMe

•atDNA only, but they include a few Y (if tester is male) & mt markers to determine both haplogroups

•They used to provide extensive reporting of medical considerations

•Test results can be uploaded to Promethease.com for similar information

•Have restored some carrier status and inherited trait reports

Testing Goals

Y- DNA

•Finding/ proving/ refuting surname connections

•Resolving uncertain paternity

•Verifying document-based research

•Determining patrilineal geographic origins or specific patrilineal ethnicity (e.g., Ashkenazi Jew)

mtDNA

•Disproving matrilineal relationships

•Uncovering matrilineal area of geographic origin

•Determining specific matrilineal ethnicity (e.g., Native American)

atDNA

•Finding cousins

•Locating unknown closebiological family

•Determining specific kind of relationship

•Determining common ancestor between two lines

•Bringing focus to document-based research

Next Steps While You Wait

•Beef up your pedigree – high quality, documented sources for all generation links, birth, marriage & death dates and locations on all lines as far back as possible (4th great-grandparent ideal)

•Do FAN work – will be especially helpful if encounter an MPE – Misattributed Parentage Event (NPE)

•Bring forward to the present as many lines as possible – those 64 fourth great-grandparents!

•Create GEDCOMs for specific lines – subsets of full tree with just basic facts for sharing with matches

•Prepare letter templates for contacting matches

Additional Resources

Books

•Bettinger, Blaine. The Family Tree Guide toDNATesting and Genetic Genealogy, Family Tree Books, 2016.

•Hill, Richard. Finding Family: My Search for Roots and the Secrets in My DNA, CreateSpace, 2012.

Blogs

•Deb’s Delvings. Debbie Parker Wayne –

•The Genetic Genealogist. Blaine T. Bettinger – cM Project

•DNAeXplained – Genetic Genealogy. Roberta Estes –

•The Independent Guide to DNA Testing. Richard Hill –

•The Legal Genealogist. Judy G. Russell – (About DNA on Sundays)

Other Web Sites

•International Society of Genetic Genealogists –

•Kelly Wheaton’s Beginners Guide to Genetic Genealogy –