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The ABCs of DNA – An Introduction to Genetic Genealogyby Debra Smith Renard, Eureka! Genealogy, Louisville, Kentuckydebra.renard@eureka-IntroductionProof 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 researchIt is used in conjunction with a well-formed pedigreeIt can support or refute our previous conclusions. Sometimes it raises more questions.It’s best to start with a specific question & hypothesisBe 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 familyDNA BasicsDNA is found in the nucleus of almost all our cellsWe inherit half of this nuclear DNA from each parentIt’s a mixture of a portion of the DNA they inherited from each of their parentsIt is contained in 23 paired packages called chromosomesFirst 22 pairs are called autosomes; 23rd pair are the sex chromosomes that determine genderFemales have two X chromosomes, males have an X chromosome and a Y chromosomeYou get one of each pair from mother, one from fatherDNA is a very long, thin moleculeIts 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 sideThe Human GenomeThe human genome (all of one’s genetic material) has about 3 billion of these base pairs of DNAFor 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 relatednessAnother important kind of DNAOutside the cell nuclei are many structures called mitochondria, the “power plants” of cellsThey contain DNA in circular molecules each consisting of over 16,500 base pairsCircle is divided into 3 main regions - two hypervariable control regions: HVR1 & HVR2, and the Coding region. Majority of markers are in the coding region.Kinds of DNA TestsCurrently three main types with variations:Y-chromosome (Y-DNA) used for patrilineal (direct paternal) lineMitochondrial DNA (mtDNA) used for matrilineal (direct maternal) lineAutosomal DNA (atDNA) tests for all ancestral lines, but useful for fewer generations backX chromosome (X-DNA) is not a separate test, but atDNA results usually include data on thisAll three types of tests provide variations of three thingsResults based on specific chemical bases in your DNAList of people in the company’s database you matchEthno-geographical origins for the lines relevant to that testY-DNAY-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 haplotypeY test results include a list of people you “match”Two kinds of Y-chromosome TestingShort Tandem Repeat (STR)A short series of base values is repeated a number of times at a particular locationWe 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., DYS393Total number of DYS marker values reported varies with level of testPossibly 12, 25, 37, 67 or 111 markers; 37 min for most genealogical purposesThe closer two results match, the closer the genetic relationshipSingle 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 generationsUse these to identify haplogroups designated with letters of the alphabet and the ancient paternal ancestry associated with themSTR test (the other Y test) can only give an estimated haplogroupSNP testing is more precise and will result in a specific sub-clade, such as E1b1b1c1a or E-PF6751 (terminal SNP)Y Haplogroup MigrationStarts from Africa, spreads to Europe & Asia, and finally to the AmericasProgressive presence of SNPs in indigenous populations enables tracking of historic migrationsMitochondrial DNA (mtDNA)mtDNA is passed from mothers to all their children, but only females pass it onBecause 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-DNARandom mutations do accumulate very slowly over time and are passed onEven distant relatives may be a close match, so least helpful test for genealogical purposesThree levels of mtDNA testingHVR1 – don’t do this one by itself any longerHVR1 & 2 together - still only tests ~7% of mtDNA sequenceFull Mitochondrial Sequence (FMS) includes entire molecule – i.e., both HVR & coding regionsTest results are expressed as a list of all your differences when compared to a reference sequenceIncludes a list of people you match within a certain genetic distanceIf exactly match on FMS, you may have a common ancestor within a genealogically meaningful timeframeMutations are passed on to subsequent generationsLike Y-DNA, used to id haplogroups with letters and associated ancient maternal ancestryThe lettering system used has no connection to that of the Y-DNA haplotreeMitochondrial Haplogroup MigrationAgain, starts from Africa, spreads to Europe & Asia, and finally to the AmericasProgressive presence of SNPs in indigenous populations enables tracking of historic migrationsAutosomal DNA (atDNA)atDNA is found in the 22 pairs of autosomesNewest type of testing, evaluates over 700,000 SNPs Inherited from all your ancestral lines through both parentsSince we get one of each chromosome pair from each parent, get 50% of our atDNA from eachThey, 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 ResultsGet 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 show locations of chromosome segments 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 relatedChart of average % DNA shared with various relationships is at ., siblings 50%, grandparent 25%, 1st cousin 12.5%, 2nd cousin 3.125%, etc.NOTE: “Half” relationships = half the shared DNA, “Double” ~ 2xIt’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 CompaniesAncestryDNAatDNA onlyNo chromosome segment analysis, but have total DNA shared with match and # of segments. Look for “i”.Extensive presence of family treesSome of newest features: Shared Ancestor Hints, DNA Circles, Shared Matches, Genetic CommunitiesCan download raw data; can also import to FamilyTreeDNAFamilyTreeDNA atDNA (Family Finder), Y-DNA STR at various marker levels, & mtDNA HVR 1&2 or FMSAlso tests for specific Y SNPsExcellent tools for autosomal analysis: In Common With (and Not…), chromosome browser, matrixAccess to many projects, especially those associated with Y test results23andMeatDNA only, but they include a few Y (if tester is male) & mt markers to determine both haplogroupsThey used to provide extensive reporting of medical considerationsTest results can be uploaded to for similar informationHave restored some carrier status and inherited trait reportsTesting GoalsY- DNAFinding/ proving/ refuting surname connectionsResolving uncertain paternityVerifying document-based researchDetermining patrilineal geographic origins or specific patrilineal ethnicity (e.g., Ashkenazi Jew)mtDNADisproving matrilineal relationshipsUncovering matrilineal area of geographic originDetermining specific matrilineal ethnicity (e.g., Native American)atDNAFinding cousinsLocating unknown close biological familyDetermining specific kind of relationshipDetermining common ancestor between two linesBringing focus to document-based researchNext Steps While You WaitBeef 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 matchesPrepare letter templates for contacting matchesAdditional ResourcesBooksBettinger, Blaine. The Family Tree Guide to?DNA?Testing and Genetic Genealogy, Family Tree Books, 2016.Hill, Richard. Finding Family: My Search for Roots and the Secrets in My DNA, CreateSpace, 2012.BlogsDeb’s Delvings. Debbie Parker Wayne – Genetic Genealogist. Blaine T. Bettinger – Shared cM ProjectDNAeXplained – Genetic Genealogy. Roberta Estes – Independent Guide to DNA Testing. Richard Hill – Legal Genealogist. Judy G. Russell – (About DNA on Sundays)Other Web SitesInternational Society of Genetic Genealogists – Wheaton’s Beginners Guide to Genetic Genealogy – ................
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