Adventures in Genetic Genealogy – Part 1 “Who’s your Daddy?”

The latest tool in every genealogist’s tool box is the DNA test.  This post will focus on the Y-DNA test, the one that men only take to determine the patrilineal line.

To best understand your results and accurately gauge your expectations you really need to know a little about the science of genetics and DNA.  It’s been a long time for me since high school biology class but here goes:  Every cell in your body contains your DNA.  Strands of DNA are wound up and organized into dense structures of genetic material called chromosomes. Humans have 46 chromosomes – 23 pairs.  DNA is in the shape of a double helix – a twisty ladder like in the picture.  The ladder rungs are called Base Pairs.  There are 4 different bases and the different sequence they fall into codes for different genetic traits.  Not all genetic traits are constantly expressed in every cell, which allows them to do different functions, like be a liver cell or a white blood cell.  On your 46 chromosomes there can be a million ladder rungs each – so you can see how many different possibilities of sequences there can be. DNA is found in the cells of all living beings from fungus to human.  It is the different sequencing that determines our differences whether it is a completely different species or just different hair color.

All of your body cells contain identical DNA, except the sperm and the egg (whichever ones you make).  They contain only 1 chromosome of each pair (23 instead of the normal 46).  So when the two combine – The Miracle of Life -- you get exactly ½ your DNA from each of your parents for a complete set of chromosomes. 

HOWEVER, even though your father and mother each got ½ of their DNA from their respective parents, it does not mean you got exactly 25% of your DNA from each of your grandparents.  Each sperm and egg is unique among themselves.  This is why you are just alike but not identical to your siblings.  When the egg and sperm are formed they don’t spilt the DNA right down the middle but take bits and pieces from each side to form their unique ½ DNA. This is called recombination.  

HOWEVER, this is not the case for the sex chromosomes.  The female sex chromosome pair is denoted XX and the male XY.  When a female makes a ½ DNA for the egg it is always contains an X.   When the male makes sperm the X and Y cannot recombine, therefore a sperm is either the same X or same Y.  So the when they combine you get a sex chromosome pair that is either XX (female) or XY (male).  Since the Y part of the pair does not do any recombination it remains FAIRLY intact as it passes from father to son.  Therefore comparing Y-DNA can match a patrilineal line -- a surname -- for several generations.

Sorry, I just wanted to add this picture

“Fairly Intact” is the key phrase in the Y-DNA test.  When DNA is copied it is not always a perfect copy.  These miscopies are called Mutations.  [We’re all X-Men!]  While the Y-DNA is pretty stable mutations will happen between generations.  This is the point where we cease being biologists and become statisticians.  Genetic genealogists have determined a method of predicting how many generations back 2 people have a common ancestor based on the number of mutations that differ between them.  This is called the Genetic Distance.  Basically the more mutations the more generations back you are related, STATISTICALLY SPEAKING.  There is no way to determine when the mutation occurred when comparing 2 men.  It could have occurred 1 generation ago or 10 generations ago.  And the best way to make any statistical conclusions is to have a large sample of data.  

Whew, that’s enough science.

My personal adventure in Y-DNA testing generated more questions than answers.  My oldest patrilineal known ancestor is Joseph W Neely (1810-1854) of Tennessee.  He died in Obion County but anything about his family – parents, siblings, marriage location – are all a mystery.  There are 3 main lines of Neelys in Tennessee, a Virginia Line, a North Carolina Line, and a South Carolina Line.  I had my dad take a Y-DNA test to see which one his YDNA matched into to hopefully break down that stubborn brick wall.

Except I didn’t match anyone named Neely at all.  Yikes.  All my matches (and none that close) were of the surname Worley/Werley/Whorley.  It seems I am a victim of an NPE – a Non-Paternity Event.  

NPE scenarios in the context of genetic genealogy

• Illegitimacy outside marriage: boy taking maiden name of mother
• Infidelity within marriage: boy taking surname of mother’s husband
• Re-marriage: boy taking surname of step-father
• Rape: boy taking surname of mother or partner
• Changeling, surrogacy, sperm donation, unintentional embryo/baby swap: boy taking surname of mother or partner
• Adoption, incl. ‘hidden’, orphan & foster: boy taking surname of guardian
• Apprentice or slave: youth taking surname of master
• Tenant or vassal: man taking surname of landlord or chief
• Anglicization of Gaelic or foreign name: man taking translated/phonetically similar name
• Formal name-change, e.g. to inherit land: man taking maiden name of wife or mother
• Name-change to hide criminal past, embarrassing surname, or a stage name: man taking unrelated surname
• Informal name-change, alias, by-name: man taking name of farm, trade or origin
• Mistake in genealogy, or in DNA analysis

Source:  International Society of Genetic Genealogy Wiki

There also are not many other male Neelys remaining in my dad’s immediate family.  Although his grandfather had 5 brothers there are only a couple of male descendants still living.   So much for my statistically significant sample of data.

So when could this Non-Paternal Event have happened?  It’s hard to pin down exactly as the mutation could have happened within the last couple of generations or many generations ago.  This is the probability chart of finding the common ancestor as provided by my testing company Family Tree DNA for my genetic distance of 3.

Generations	Percentage
4	11.98%
8	47.04%
12	76.08%
16	90.98%
20	96.98%
24	99.07%

So I need to go back 16 generations to get a 90% chance of a match.  As my dad is only 4 generations removed from Joseph I have a ways to go back.  If you average a 35 year gap for each generation, that is a total of 560 years – so about 1400 AD.  I am of European descent.  Surnames only began gaining popularity around that time.  First surnames were only for aristocracy then commoners began adding surnames to indicate personal attributes, location of origin, occupation, parentage, patronage, adoption, or clan affiliation.  So even brothers may have different surnames:  Robert (the Black) Smith could be brother to John (the) Shepherd to James (the son of) John(son).  Outside of royalty, familial documentation this far back is practically non-existent.  So statistically speaking I have no chance of making a connection.

Back to the sample size.  Family Tree DNA claims to have about 500,000 men in their Y-DNA database.  Given that there are about 325 million people in the United States alone, their sample size is still quite small – about 0.3%.  

So for now my Joseph is still an enigma.  Unless a fellow genealogist someday matches DNA with him, old-school genealogy will just have to solve this puzzle.