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Jack O'Neill and Cameron Mitchell have been Y-DNA tested and have a 66/67 STR marker match*. This match was extra surprising because Cameron and Jack are workmates, and their other workmates have been giving them very strange looks since finding out the results (and cryptically whispering about "mission #30185", and solar flares in 1969) . What makes this even more mysterious is that Cameron Mitchell has an uncanny resemblance to Jacks long lost nephew, John Crichton (who mysteriously went missing ten years ago)...
... What can they do to find out how long ago their common ancestor lived?

Was it 39 years ago or was it 399 years ago?

To answer that question, first I need to explain about the different types of DNA that can be used to help genealogy. There are different inheritance patterns for different types of DNA. The purpose of this set of pages, is to explain the different inheritance patterns for the different types of DNA, and how this can help us with our genealogy.

* Although this is a fictionalised scenario, it provides a realistic example of how autosomal DNA testing can compliment traditional paper trail genealogy, and the Y-DNA STR testing that is usually done in genetic genealogy.

 

* Cells and DNA Basics
* Meet the O'Neills
* DNA Inheritance patterns
*Can Autosomal tests help with traditional Genealogy?
*The O'Neill/Mitchell example

Cells and DNA Basics

The first thing that we need to do,.. is look inside a human cell, and have a look at where we find the different types of DNA.
Inside the cells in our body, (eg. in our cheek cells) there are many different components called "organelles".
The two "organelles" that are most important for discussions about human DNA and genealogy are the Nucleus and the Mitochondria.

 

In the nucleus of each cell there are 23 pairs of Chromosomes, - one pair being the sex chromosomes (two X's in women and an X and a Y in men) and the 22 other pairs are usually referred to as "autosomal".
There is also a completely different kind of DNA , called Mitochondrial DNA (or mtDNA for short). Mitochondria are the "power generators" in each cell. Mitochondrial DNA is completely separate from the DNA in our Cell Nucleus, and Scientists think that in the past Mitochondria were separate organisms that lived in symbiosis with the cell.

There are different inheritance patterns for these different types of DNA. The purpose of this set of pages, is to explain the different inheritance patterns for the different types of DNA, and how this can help us with our genealogy.

To make things clearer, I will now show how we inherit our DNA from our parents. We get 23 chromosomes from our father, and 23 chromosomes and all our mtDNA from our mother.

From our Fathers we get: From our Mothers we get:
22 autosomal chromosomes
1 X chromosome or 1 Y Chromosome
(two types of sperm)
22 autosomal chromosomes
1 X chromosome
  Mitochondrial DNA

 

So,.. we have:
A)46 Chromosomes (Nuclear DNA)
        i. Autosomes (22 pairs, 1 of each pair from each parent
       ii. Sex chromosomes (1 pair, 1 of each pair from each parent)
          1) X Chromosome (Females have two, Males have one - everyone has 1 from their mother; females have a second from their father)
          2) Y-Chromosome (Males have one, Females have none)

In very rare cases there may be additional autosomal chromosomes, (eg. Down syndrome), or additional sex chromosomes (eg. Klinefelters syndrome,) or sometimes there is only one X chromosome (ie. Turner syndrome), or there may be missing parts ("deletions") of autosomal chromosomes (eg. Williams syndrome)

B) Mitochondrial DNA (all people have mtDNA. The mitochondrial DNA is inherited only from the egg, not the sperm. Sperm do have mitochondria in their "Neck", but these aren't transferred into the egg, because there are mechanisms to prevent this from happening).

 

 

Meet the O'Neills

Before I show a summary of the difference inheritance patterns, and their advantages and disadvantages for genealogy, I will first introduce you to the Fictional O'Neill family". I use the O'Neill family to provide family tree examples, to help clarify the different inheritance patterns (especially for the section on autosomal DNA).

Seamus O'Neill               Anderina Mikita
                     Niall O'Neill                           Joeline Goldsmith
                                                 Patrick O'Neill                       Robina Cooper
                                                                                                   John O'Neill                          Brandy Wright     Jacob Carter               Paula Mallozzi
                                                                                                                 Leslie O'Neill   Jack O'Neill                                  Samantha Carter
 
                                                                                                     Olivia Crichton               Jacob O'Neill Jolinar O'Neill Daniel O'Neill

 

For clarification:

Females - are represented by a circle symbol

Males - are represented by a Square symbol

Younger generations are towards the bottom of the diagram, and older generations are towards the top of the diagram. The direct paternal line is at the left of the diagram, and the direct maternal line is to the right (not shown as fully as the paternal line).

Jacob O'Neill, Jolinar O'Neill, and Daniel O'Neill are full siblings. Their parents are Jack O'Neill and Samantha Carter. We can see from the diagrams that their paternal grandfather was John O'Neill, and their maternal grandfather was Jacob Carter. We can also see that their direct paternal line great great great grandfather was Seamus O'Neill (ie. their fathers fathers fathers fathers father).

If you look at the fictional O'Neill family, you'll see that the square (males) or circle (females) depicting 8 of the family members are shaded grey. Although the O'Neills are fictional, a real family* has been used to represent the genetic data of 8 individuals in the O'Neill family. Later, I will be showing some chromosome diagrams showing real examples of Chromosomal inheritance from grandparents. The chromosome inheritance diagrams are the result of comparing the genomes of 6 of the 8 people represented in grey.

*They are the same as the 23andMe Mendel family - but their real name is neither O'Neill nor Mendel.
The real person whose data is represented by "Samantha Carter"/"Lily Mendel" is a well known person in the development of personal genomics.

 

First I'll show diagrams showing the mathematical average inheritance percentages per ancestor for the different types of DNA, and then I will show some real life examples of the %'s of DNA inherited from grandparents, and how it can vary from the theoretical mathematical average. Finally I will show some diagrams showing the theoretical mathematical averages shared between different levels of cousinship.

How can DNA help us with genealogy??

There are different inheritance patterns for these different types of DNA. The purpose of this set of pages, is to explain the different inheritance patterns for the different types of DNA, and the different ways that these different types of DNA can help us with our genealogy.

Below is a summary table showing the different types of DNA, the advantages and disadvantages of each, and a thumbnail diagram of each showing the average inheritance percentages per ancestor.

Each thumbnail diagram links to a separate page that discusses that type of DNA in more detail. At present, the page on autosomal DNA is more complete, and additionally contains a diagram which shows the average amounts of DNA shared between different types of cousin. It also contains three diagrams, -1 each for Jacob O'Neill, Jolinar O'Neill and Daniel O'Neill - which shows real life examples of the %'s of DNA that can be inherited from grandparents.

Type of DNA
Clonal or Recombinant?
Advantages
Disadvantages

Autosomal DNA

Click on Thumbnail to see in more detail

Totally recombinant
(ie. gets mixed up between the pairs of chromosomes each generation)

Equally representative of all your ancestral lines*.

If you get a "relative finder" or "family finder" match with a person who isn't a previously known cousin, the amount of matching DNA can give an indication* of how many generations ago the common ancestor lived.

(*In theory, but in practice there is a degree of inherent randomness in the recombination process. The closer the relationship, the smaller the margin of error. See autosomal page for more details)

Can't always trace to specific ancestral lines.


If you get a "relative finder" or "family finder" match with a person who isn't a previously known cousin, the DNA itself won't tell you where in your respective family trees your common ancestor is, only paper trail comparisons can.

mtDNA

Click on Thumbnail to see in more detail

"Clonal"
(doesn't get mixed up)
Can trace to specific ancestral lines with 100% accuracy.

Not representative of your whole genome/ancestry. Only represents one ancestral line out of many. (direct maternal line).

Doesn't identify how many generations ago the common ancestor was (it might have been thousands of years ago)

Should never assume that your Haplogroup is representative of your total ancestral/ethnic identity.

Y-DNA

Click on Thumbnail to see in more detail

"Clonal"
(doesn't get mixed up)
Can trace to specific ancestral lines with 100% accuracy.

Not representative of your whole genome/ancestry. Only represents one ancestral line out of many. (direct paternal line).

Doesn't identify exactly how many generations ago the common ancestor was (The number of matching markers can give a general indication but only paper trail can say precisely who the common ancestor was)

Should never assume that your Haplogroup is representative of your total ancestral/ethnic identity.

X-DNA


Click on Thumbnails to see in more detail

Alternates between:

 

Recombinant in Females and

 

Clonal in Males.

 

 

Can help narrow down which ancestral lines matches are from.

Representative of a much smaller subset of your ancestors. Some ancestors contribute much more (ie. those of ancestral lines of alternating gender eg. mothers fathers mothers fathers mother). Some ancestors don't contribute any (ie. paternal lines).

Complicated inheritance pattern.

Not representative of your whole genome/ancestry

Some ancestors contribute more, and some ancestors don't contribute at all.

*Recombination: Process in which your parents mixed your grandparents (ie, their parents) Chromosome pairs together. See the "Meiosis and Crossover" page for more details

Can Autosomal tests help with traditional Genealogy?

Yes. Autosomal testing can help with genealogy in several different ways, complimenting the Y-DNA and mtDNA analyses that have been used in the last 10 years in conjunction with traditional paper trail genealogy,.

As an example:
(This scenario is fictionalised, but represents a typical scenario)

Jack O'Neill and Cameron Mitchell have been Y-DNA tested and have a 66/67 STR marker match. Both of them also have other close matches of others with the O'Neill surname. It seems possible that there has been a "non-paternal event" in Cameron Mitchell's direct paternal line at some time in the last 30-300 years.

Jack and Cameron's Y-DNA results tell them that they definitely had a common ancestor somewhere along their respective paternal lines, but it doesn't give them any precise information about when that common ancestor lived. By testing their autosomal DNA as well, they might be able to get a much better idea of when that common ancestor lived.

If, for instance they were found to share 0.2% of their autosomal DNA, then this would be more-or-less consistent with them being fourth cousins, and would suggest that their common ancestor most likely is Shane O'Neill (but might instead be Conn O'Neill or Seamus O'Neill). This of course assumes that they only have one common ancestral line. If they have more than one ancestral line in common, then not all of the DNA that they share will be from the O'Neill ancestral line.
If it was found that on a different family line they are 3rd cousins once removed, then if you take this second line of common descent into account, the amount of DNA shared from the direct paternal ancestral line could be considered negligible, and the common descent therefore even more distant.
On the other hand - perhaps there is a second alternative. Jack and Cameron's documented paper trail link is also via the O'Neill ancestral line. According to the paper trail, Cameron is descended from the elder sister of Jacks great grandfather. Seamus O'Neill was the father of both Niall O'Neill and Catherine O'Neill. If Cameron was a paternal line descendant of a son of Catherine O'Neill, then an alternative explanation could be that Catherine's son was actually the son of Niall and an undocumented woman. However, the paper trail shows that Cameron's mother was a maternal line descendant of a daughter of Catherine's , rather than Cameron's father being a paternal line descendant of a son of Catherine. Therefore, that is not the explanation.

Since there are two different ways that Cameron is related to Jack, one via Cameron's mothers ancestors and the other via Cameron's fathers ancestors, the easiest way to ascertain how much of Cameron and Jacks shared .2% is from their shared direct paternal lineage would be to have Cameron's father tested. Of course, if the .2% DNA that Cameron and Jack share is in a single chromosomal segment, then this would suggest that all of the .2% is from a single ancestor (again, we wouldn't know whether this would be from the shared ancestry from Cameron's mothers or fathers side, unless either his mother or father or both are also tested.
Overall, the testing done so far has so far proved that the common ancestry between Cameron and Jack goes back more than 3 generations. Since they have more than one common line of descent, if they want to further pin point how far back their common ancestry along the O'Neill line is, Cameron should also have his father tested (testing his Grandfather would have been even better, had he still been alive).

It is interesting to note that the surname "Mitchell" has multiple origins, one of which is derived from the Irish Ó Maoilmhichil. The Irish Mitchell's were associated with the O'Donnell clan (who were often rivals of the O'Neill clan).

 


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2010