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DNA Basics

Discover the basics – or delve into the details – of DNA. Here is the long and short of how DNA testing works and how you can use it in your genealogical research.

Thank you to Society member George LaPlante, who also moderates the DNA SIG (see below), for compiling this information.

Disclaimer: Listings on this page do not constitute endorsement by the Society.

DNA in Genealogical Research

You might already be familiar with how DNA testing can help solve crimes, confirm the paternity of children, and even determine the identity of ancient mummies.

Now DNA can also help you with your genealogical research:

  • DNA testing makes your family tree grow taller by identifying your unknown direct ancestors (like a great-great-grandparent).
  • It widens your family tree by identifying other relatives who might be unknown to you (DNA “cousins).
  • It also tells you about your ethnicity, how your ancestors lived, and their cultural experiences, which adds color and details to the leaves on your family tree.

It’s a simple and painless process to gather your DNA sample and within a few weeks have results that you can compare with ever-expanding DNA databases to find potential genetic cousins.

Used in conjunction with traditional methods of genealogical research, DNA can help you break down brick walls and lead to new and exciting discoveries.

DNA is a “Blueprint” 

Think of your DNA as a blueprint that governs the construction of the unique individual that is you. Replicated in almost every cell in your body, your personal blueprint consists of about 3 billion individual instructions called nucleotides.

In humans, double helix strings of DNA (nucleotides) make up our 46 chromosomes in 23 pairs, with one of each pair inherited from each of our biological parents

Chromosome pairs 1 through 22 (autosomes) are numbered by size from longest to shortest.

The 23rd pair (sex chromosomes) consist of an X chromosome from each parent in women, while men receive an X chromosome from their mother and a Y chromosome from their father.

In Essence, DNA Tests Look for “Cousins”

Autosomal DNA (atDNA) tests examine strands of DNA on chromosomes 1 through 22, as well as on the X chromosome(s). These are compared to the results from millions of other people in search of “DNA cousins” – individuals who descend from one or more of your recent common ancestors.

Matching strands of DNA are measured in centimorgans (cM). The number of cMs of DNA that you share with another person provides clues as to how closely you might be related — the more cMs, the closer your relationship. This number can also clarify, prove, or disprove possible relationships appearing in your family tree.

Autosomal tests have additional benefits beyond the discovery of hundreds, or even thousands, of previously unknown relatives. Test results are compared to reference populations to provide ethnicity estimates, for example.

Deeper Dive: How DNA Determines Ancestry

Mitochondria are structures within cells that provide the chemical energy that allows them to function. Each mitochondrion contains a relatively short circular strand of DNA (mtDNA) that is passed down from mother to child. This DNA can be sequenced and compared to that of others to look for connections on your matrilineal (mother’s, mother’s, mother’s, etc.) line in addition to identification of your maternal haplogroup (or deep history). This indicates the population of origin from thousands of years ago of your matrilineal line.

Testing a man’s Y chromosome (yDNA test) examines the Y chromosome to count the number of times certain patterns called Short Tandem Repeats or STRs (pronounced “stirs”) appear at specific locations. STRs can indicate common ancestry on the patrilineal (father’s, father’s, father’s, etc.) line and your paternal haplogroup.

First Steps: Get Tested

Start by taking a DNA test from one or more of the five companies listed below. Each company provides its own set of tools for organizing and working with your DNA test results, and each tool set has advantages and disadvantages when compared to the others. Consider how to best accomplish your research goals before moving forward. Generally speaking, the more databases you participate in, the better off you will be.

Society volunteers can assist with making that decision, so don’t hesitate to ask. Contact

DNA Test Companies: (for genealogical or ethnicity purposes)

Each company provides access to a portion of what they have to offer for a small, one-time fee (or even at no cost, see below). Additional services are provided at additional cost.

Tip: Wait for a sale to purchase your test. Sales and promotions are frequent and save you money.

  • AncestryDNA  – autosomal only
    • Largest DNA database currently available for genealogical research
    • DNA test results from other companies cannot be uploaded to the Ancestry database
    • Your Ancestry results can be downloaded to your computer and then uploaded into other databases for free
  • 23andMe – autosomal, plus haplogroups
    • Oldest and second-largest DNA database currently available for genealogical research
    • DNA test results from other companies cannot be uploaded to the 23andMe database
    • Your 23andMe test results can be downloaded to your computer and uploaded then into other databases for free
  • MyHeritage – autosomal only
    • Smaller database than those of Ancestry and 23andMe
    • Particularly useful for those with ancestors who came from Europe
    • If you have test results from another company (Ancestry, 23andMe, FamilyTreeDNA, or Living DNA), download them to your computer and then upload them to the My Heritage database for free
  • FamilyTreeDNA – autosomal, yDNA, mtDNA
    • The only company that performs yDNA (patrilineal) and mtDNA (matrilineal) tests
    • If you have test results from another company (Ancestry, 23andMe, MyHeritage, or Living DNA), download them to your computer and then upload them to the FamilyTreeDNA database for free
    • Provides access to group projects relating to your test results
    • Smaller database than those maintained by Ancestry and 23andMe
    • This database may be used by law enforcement agencies to help solve major crimes. Your DNA cannot be seen by law enforcement agencies without your specific consent.
  • LivingDNA  – autosomal, haplogroups
    • Smaller database than those of Ancestry and 23andMe
    • Particularly useful for those with ancestors who came from the British Isles
    • If you have test results from another company (Ancestry, 23andMe, FamilyTreeDNA, or MyHeritage), download them to your computer and then upload them to the LivingDNA database for free

Additional Genetic Genealogy Analysis Tools

  • DNA Painter
    • Shared centimorgan (cM) tool
    • DNA chromosome painting
    • WATO (“What are the Odds”) tool
  • GEDmatch.com
    • A genealogy database consisting of DNA test results uploaded by people who have tested at one of the 5 companies listed above. It is unique because it allows users greater access to view the DNA data of people they match.
    • This database may be used by law enforcement agencies to help solve major crimes. Your DNA cannot be seen by law enforcement agencies without your specific consent.

More Resources

  • Books
    • “Family Tree Guide to DNA Testing and Genetic Genealogy, Genetic Genealogy in Practice” by Blaine T Bettinger
    • “Genetic Genealogy: The Basics and Beyond” by Emily D Aulicino
    • “Guide to DNA Testing: How to Identify Ancestors, Confirm Relationships” by Richard Hill

Society DNA Meetings 

Get your questions answered and join in DNA discussions at these Society meetings:

  • DNA Lunch & Learn
    • Every 3rd Friday, noon – 1:30 p.m.
    • Currently meeting on Zoom
  • DNA Interest Group (DIG)
    • Every 3rd Saturday, 9:30 a.m. (before Society Meetings)
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