How does a DNA test determine kinship?

So ... How does a DNA test work, how are they able to determine degrees of kinship?   The simple answer is "shared DNA".
To understand this more, you need to first visualise that every person is made up of 23 chromosome pairs AND that these chromosome pairs are represented as 23 bars/rods as is shown in the picture below.

These 23 chromosomes are displayed on what is called a Chromosome browser.
Below is a closer view of a "blank" Chromosome Browser produced by FTD
Family Tree DNA   Note that the Chromosome pairs are varied lengths, which is why they are different lengths in the browser.  You will get accustomed to this in time.

An autosomal DNA test gives you results/matches for chromosome pairs 1 - 22. 

If you are Female, an mtDNA test will give you results/matches on your 23rd Chromsome pair, shown in the image as x.  If you are Male, a Y-Chromosome test will give you results/matches on your 23rd Chromosome pair, and instead of showing an 'x' - as in the picture above, it will instead have the letter 'y'.   

For the purposes of this blog, and for mapping ancestors in a DNA context we are only concerned with an AUTOSOMAL DNA TEST RESULTS and therefore only the first 22 chromosome pairs. 

Now, when you receive your test results [your match list of relatives] they have shared DNA at various chromosome placements.   For those readers, that like me have had their DNA tested by Ancestry.com;  you will not "see" which chromosome pairs who share with your DNA matches.  Ancestry works it out for you and merely gives you an overall kinship estimate.   Life would be so much easier if Ancestry.com provided a chromosome browser! 

However, there is an option at Ancestry.com that allows you to download your RAW DATA.  Once you have done this, you are able to UPLOAD it to sites on line that DO have a chromosome browser.    Sites that I have used and have had success with are "Family Tree DNA" and "Gedmatch".  

I use both sites, so I am able to easily ascertain the precise location of shared DNA with one of my matches.  For example, David [surname removed] from Australia has shown up as a DNA match list in Family Tree DNA.  He and I share 64 Centimorgans and therefore Family Tree DNA estimate that the relationship range between David and I is 2nd - 4th Cousin.  However, I do not know David, nor do I know how he and I are related.  David has a family tree attached to his results, I do not recognise any of the names in his family tree.  

David is reckoned as being somewhere between a 2nd - 4th cousin based on 64cM of shared DNA.

Furthermore, what these large companies don't tell you up front, is that the "Longest block" is what matters the most!   The focus should be on the longest block shared; which is 22 centiMorgans long, rather than the figure of 64 centiMorgans.    A kinship estimate based on an overall total can be flawed, particularly if that overall total consists of lots of small blocks of DNA.  

This is particularly important when looking at shared DNA of Polynesians or other first nation peoples with small gene pools.  I will cover this in more detail in another post [coming soon].

The longest block I share with David is 22 centiMorgans, so this would definitely mean 4th cousins as opposed to 2nd cousins.   This will take some work to establish the connection but its still relatively close enough to work out if there are family genealogists on both sides willing to put in the effort.  Thankfully there are - and I will be reporting on the progress with David as I go along.  

Below, is what the shared DNA between David and I looks like on a Chromosome Browser.   Our shared DNA sits on Chromosome 4 and Chromosome 12.

The Chromosome Browser will also give you more precise figures for location.

These figures may not mean much in isolation.  However, over time other matches may land in this same area, particularly matches that you may actually know how you ARE related to already.  

DNA is not a quick fix, unless you are lucky enough to stumble across close relatives.  It still requires you to map out in your Chromosome pairs where particular DNA has been inherited from particular ancestors.  

As it happens, I have begun to map out my Ancestors, and the position where David's shared DNA falls on Chromosome 12 seems to be DNA inherited from my REID side.  There are already two other matches at that placement, who are related to me via that lineage - which is why REID is recorded next to their name.  Everyone at this placement is related to each other, whether we know how or not.  David is my relative, as well as being Carew's relative and Tracey's relative.   At the time of writing this post, I am about to make contact with Lynette, David's sister; to see if Newfoundland and Canada mean anything to her in terms of her Family Tree.  Watch this space for updates.

In the next blog post, I will be talking about how you can store the information of your matches on a DNA painter.   At the same time I will be working on a post explaining the necessary approach when dealing with Polynesian DNA. 

Please ask questions in the comments box below, if you found this post difficult to understand. 

Mauri ora!  [Bless you!]

By word of a cousin's mouth - An Introduction

Some time in 2017, my cousin "Marsh" purchased a DNA test from Ancestry.com.  The test involved placing saliva into a tube and sending it to Ireland in a postage paid box.  What seemed like a month later,  he'd received his results back.   There were two parts to these results.
(1) Ethnicity estimate - a break down of culture by location.  Polynesian was his highest, and then Great Britain and various smaller percentages [which will not be a focus of this blog]
(2) A Match list - a list of relatives, identified on the basis of shared DNA with people already on their database.

"Marsh" told me that "Neil" one of our other cousins, was on his list as a second cousin. Do the results actually "name him" as in, his full name ? I asked with growing interest.  He replied with a resounding Yes !  I was like - Wow !!!  "Uncle Joe's on the list as well, his daughter and his Grandson" he added ... as well as naming a number of other mutual relatives.  He told me, that there were 'pages and pages' of matches.  I couldn't help but think about the potential of DNA tests for ancestry purposes.  I hadn't realised that this test was on such an intimate yet large scale.

I work as a historian, and most of my spare time is spent tracing lineage.  I would describe myself as an enthusiast of genealogy.  I had been interested in Matrilineage (I still am) and after reading about it, I considered taking an mtDNA test.   This test uses the gender chromosome pair (chr. 23) to trace the direct female line (matrilineage) to a Clan Mother, and therefore a haplogroup.
Google mtDNA, Haplogroup, Clan Mother if you'd like to know more about this. 

The test Marsh, and other relatives of mine had taken was an autosomal test.  This gathered material from the other 22 chromosome pairs and provided usable data for all sides of the Family Tree.  An autosomal test, covered 250 years worth.  A time period equal to roughly 10 generations.

NOTE :  We all have 46 chromosomes, that are arranged in 23 chromosome pairs.    One of each pair comes from Mum, and the other from Dad.  The 23rd chromosome pair decides our sex.  Mum puts up an X, if Dad also puts up an X, the child is a girl.  If Dad puts up a Y, the child is a boy.   The 23rd chromosome pair is used for both mtDNA tests and Y-Chromosome tests for Males. 

On some of the branches of my family tree I can trace my descent from significantly more than 10 generations.  For example, I am a 23rd generation descendant of Hoturoa, the Commander of the Tainui Waka (Canoe).  Many people can trace this descent, because this genealogy has been preserved.   On my English side, I can trace a similar amount of generations from the original ancestor of the Ingpen (Ingpenne, Inkpen) family, a noble family of co.Berkshire.  Again because this lineage had been preserved.

Yet, on some branches, they were unknown, neglected and quite forlorn.  An autosomal test could help me in identifying lost lines.  I might find relatives, who knew the lineage, or who at least had the family names and might be associated with the relevant places.  So I did it.  I ordered the test, contributed my saliva, posted it back and about 4 weeks later, I too - had some results.

Admittedly I went straight to the match list.  The very first name on my list as a second cousin, was *Neil.  "Spot on" ! he was a first cousin to my late mother and therefore, my second cousin.   His Father and my Grandmother, both in good health are siblings.  Awesome! I am who I say I am.  Not that there was ever much doubt, but this was unfamiliar territory and one never really knows - until one knows!  Any fears I may have had were quickly dispelled when I saw Neil's name, and everybody else Marsh had named including him.  [A sample of the match list is pictured below, as well as the estimated relationships based on shared DNA].
NOTE : I have removed the surnames of my relatives below, for their privacy

Another relative, Uncle Ray also showed up on my match list.  Interestingly enough, the kinship relationship between Uncle Ray and I, and Uncle Joe and I is the same, yet Uncle Ray showed up closer.   All this meant was that he and I inherited more of the same DNA.  Its just the way it is some times and as it was my first introduction to autosomal DNA testing, I was happy enough to see those six matches on my list.  I have arranged these six matches into a family tree, to show the kinship relationships we have with each other.
Note : The silhouettes shaded in grey, indicate that these members of the Family tree have passed on. 

Proven! DNA testing was able to identify both my relatives and an estimated degree of kinship.  In this initial case, it was easy, because the descent lines were already known.   It still serves as a useful introduction to DNA for ancestry purposes.  Further into the blogs, I'll discuss various strategies for matches with relatives that we are yet to meet.