DNA applications

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For genealogical purposes use DNA testing with paper records, relies on database matching. Can use to verify your family tree, find lost relatives, break down brick walls.

Nuclear DNA has 46 chromosomes in each cell; 22 pairs of aurosomes, one pair of sex chrom; Single pair is madde up of XX female and XY male (first from mother and next from father).

Legal points:

  • GDPR applies to your data eg: storage limits, accountability, accuracy, confidentiality, purpose limitation
  • Law enforcement use some databases. GEDmatch (USA) are used by law enforcement. The whole database has opted in for matching to undientified remains.
  • FamilyTreeDNA - were working with the FBI without telling customers but now you are asked if you want to be part of the law enf. matching.
  • GeneByGene, Ancestry and 23andMe are mst secure and committed to security.

Types of testing:

  • Y chromosome
  • Mitochondrial
  • Austosomal for adxiture
  • Austosomal for cousin matching

Y Chromosome test

Only for males or need a male relative. Useful to follow the surnames along the male line.

FamilyTreeDNA only company doing it for matching. Only useful if you surname is already in the DB. Many surname and georaphical projects are run by volunteers within FamilyTreeDNA.

37 marker test is enough if using with paper records. More markers useful for going back to medieval times.

Guild of One-Name Studies also have surname DNA projects.

Want genetic distance no further than 4 for closer in time. Firther back is medieval (deep ancestry).

Mitochondrial test

This DNA is passed to all children by the mother. Looks at recent and decent ancestry as the DNA changes slowly. Matches can go back 1000s of years

Not as useful genealogically. Most expensive of the entry level tests. Only FamilyTreeDNA has matching genealogy db for this.

Ideally want exact matches = genetic distance of 0. Even this can be 22 generations back.

You get deep ancestry in the form of haplogroups and there are Haplogroup projects.

Autosomal test

Get 50% from each parent. Covers all ancestral lines for 200-250 years. Best matches are with cousins of 5 or 6 generations. Chances of matching past 6th cousin is low. At grandparent level the DNA you inherit varies a little, then halves as you go back, eventually ancestors drop off your tree.

Helps to have other relatives tested, esp. older ones and 2nd cousins.

Current tests based on sampling of SNPs not the whole genome.

Still need to go back to paper records to ID actual relationships

Focus on the matches sharing the most DNA. want to group your matches into clusters and then do your own research to check relationships and find who is the common ancestor. Compare to others in your family and check the % match the realtionships you are expecting. Using centimorgans (cMs) - want at least 30cMs shared. Focus on these. Likelihood of single recent common ancester eg: 30-35 cMs (95%); 45-60 cMs (99%); 60 cMs (100%).

Companies re autosomal DNA

Some companies allow you to transfer your results over from other tests.

Get ethnicity estimates and cousin matching.

Ethnicity is matching to 1) reference populations of a geographical area - companies have different names for this and use different algorithms. LAst 500-1000 years. % change when there are updates to the db, so focus on the higher %. 2) genetic communities/regions, linking through rectn shared ancestry. More accurate and useful for genealogy.

FamilyTreeDNA/Ancestry best for genealogy as have 20 mill people on their db. Can enter your ancestral surnames. In your results look at % of shared DNA and cMs shared. Can create private and non searchable trees to try to find a relationship between you and a match. Has a ThruLines feature linking family tress to your DNA. Inc. common ancesty hints to use as clues but they can lead you in the wrong direction, esp. with small matches on wrong side of family.

23andMe (USA) more health based. HAve 12+ mill on db.

MyHeritage have c.5 mill on db. Better for Europe. Do county breakdowns and will give you some family tree hints. HAve an autocluster function where you try to ID the common ancestor for that cluster.

LivingDNA (UK) small db but provide good regional breakdowns for the UK. Trying to use people with 4 grandparents from one region. May also find people who haven't tested elsewhere.

Note: endogamour population (eg: Jewish, Orkney) interbreed over many generations.


  • Start with AncestryDNA
  • Build your family tree
  • Focus on top matches
  • Transfer to MyHeritage/FTDNA/LivingDNA
  • Use FTDNA for Y tests and mitoch. tests
  • Use 23and Me for health and trait reports.