Genetics and DNA Basics Part 1

In order to understand all of the information on this site, you’ll need an understanding of genetics and the ways we can use DNA to confirm relations that we’ve plotted through standard genealogy. If you care nothing about genealogy, these pages may still be of interest to you. We’ll cover genetic basics, the three main types of DNA testing and what they are useful for and how they generate your heritage reports.

First off, I’m not a geneticist, professional genealogist or anything remotely resembling an expert on any of the items I’m going to discuss. This is a hobby for me and I’ll try to explain this stuff in terms that I and hopefully you can understand. Any inaccuracies or mistakes are entirely my own. I’ll try to cite where I get information but I’m also not an academic. I’ll make mistakes.

Genetics is basically the study of the building blocks of all life on Earth. The structure or function of any plant or animal life is determined by its DNA. Human DNA structure is a double helix. It looks like a ladder that has been twisted. dna helixThere are 4 building blocks of DNA that are abbreviated A T C G  that combine to form base pairs.  In the 23 pair of chromosomes that we carry, there are roughly 3.2 billion of these base pairs. Over 95.5% of those base pairs are identical in every human being. It’s that remaining 4.5% that makes each of us unique. Every human being alive today traces their ancestry back to a common male ancestor in eastern central Africa about 100,000 years ago. We are all cousins.

The chromosome pairs are numbered 1-22 basically in order of size. Chromosome 1 is the largest, etc. The 23rd chromosome pair are the sex chromosomes. Men inherit a X chromosome from their mothers and a Y chromosome from their fathers. Women inherit X chromosomes from both parents. The image below shows a normal human genome. Clicking on the image takes you to the site I obtained it from.

human karyogram


Chromosomes 1 through 22 are called the autosomal chromosomes. That means that every generation, the DNA from both parents is sliced apart, chopped into segments and then recombined. It’s that process that helps life evolve and it also keeps us all from being twins.

The only standing rule that governs our DNA inheritance is that we get 50% of our DNA from our fathers and 50% from our mothers. That same percentage does not necessarily follow upstream to our grandparents and beyond.  Here’s a hypothetical example using my family.

dna passdownEach of my parents received 1/2 of their DNA from their parents. I color coded this to make it easier to see. If you look closely, you’ll see that myself and both my sisters also received exactly 50% of our DNA from each of our parents. What’s different is that in each case, our parents grabbed different amounts of DNA from their parents to make up the half they sent to us. In this hypothetical example, I got far more Adams DNA than did my sister Pam. My sister Deb got the largest amount of Austin DNA.  This example is important because it points out why it is a good idea to get as many family members tested as possible.

I can also use the above diagram to discuss the ethnicity reports that the testing companies generate. They compare certain base pairs along your genome for markers that are known to originate from a certain area. The problem is that the randomness of DNA makes those tests less accurate. Let’s assume that in the above example, that Adams was 100% Scottish. Luster was 100% English from London. Austin was 100% Irish and Clack was 100% French ( from Le Clerc).  The ethnicity reports on myself and my siblings would be roughly:

  • Me
    • British  Isles – 40% (25% Adams[Scottish], 10% Luster[British], 5% Overlap)
    • Ireland –  20% (10 % Austin[Ireland], 10% Overlap)
    • France – 40% (Clack)
  • Pam
    • British  Isles – 50% (5% Adams[Scottish], 35% Luster[British], 10% Overlap)
    • Ireland –  30% (25 % Austin[Ireland], 5% Overlap)
    • France – 2o% (Clack)
  • Deb
    • British Isles – 55% (20% Adams[Scottish], 20% Luster[British], 15% overlap)
    • Ireland – 35% (30% Austin[Irish], 5% overlap)
    • France – 10% (Clack)

The overlap I mention above is that the geographic areas that the testing services use overlap each other. Even someone that is 100% British might test 10% Irish due to these overlap areas. As you can see, there is a large variance between the results between three siblings. In the real world with literally hundreds of ancestors providing a portion of your DNA, the differences are even more pronounced. At the current level of technology, the ethnicity reports you get from Ancestry, 23andme or Family Tree DNA are good to the continent level. Once you zoom in closer than that, the speculation goes up pretty quickly. By looking at Y DNA, autosomal results from multiple close family members, mitochondrial results on both my mother and paternal grandmother, a new DNA test called Living DNA that Debi and I both took and just received results on and most importantly the known paper trail on our ancestors- Here’s what I’ve come up with for us as good estimates –

Britain & Wales – 47 %. Primarily from the northern, western and coastal areas of England. Our male haplogroup L-1 were a sea going people from up around Belgium to Amsterdam to Finland. They migrated the the British Isles as part of the multiple invasions of Great Britain – primarily the Anglo-Saxon and Viking Invasions. They primarily stayed in coastal locations. A significant portion of our British DNA comes from Northumbria – the area on the border with Scotland.

Scottish – 15%. Our Clans include Clan McRae and McLeod, Campbell, Stewart, Bruce and potentially Adams (Brick wall around 1800).  Other than Adams, some of our closest Y DNA matches are Bells, Elliots and Grahams which were all Scottish border-reiver families.

Irish – 10%. Beside the Scots/Irish lines we have, we also have Irish origins for our Austins, Baileys, Kellys and Woods in our ancestry.

Germany/Denmark – 10% We have two separate lines that are clearly German but we also have a number of Norman lines in England. The Tyrell (Terrell) line came to England with William the Conqueror and they held continuous knighthood for over 500 years.

Scandinavia – 8%. Again part of the Viking background of my paternal lineage.

France – 3%. The Clack line goes through England but they were originally French. We have also have Ancien and Bonnett as surnames of French origin.

Iberian Peninsula – 3%. This one has me stumped. Both my sister and I show 3%. My dad shows even more, so it’s valid. I just have no idea how it got there. More research needed.

Eastern Europe – 3 %. Our last known immigrant to the United States came from Hungary around 1810-1815. His name was George Fisher (Sagics) and he was a legendary scoundrel. I’ll devote at last one full post just on him.

Native American – 2%. We have a number of possible paths for that but two known sources are my 10th great grandmother Princess Matoaka Pocahontas Rolfe and my 5th great grandmother Nancy Ga Ho Ga Lightfoot.

Next post we’ll cover the three other types of DNA tests that are used in genealogy and how they can help you. I’ll also cover matching more in detail and how to use your Ancestry/23andme/FTDNA results to help grow your family tree in a later post.