What is YDNA testing

Please note that this article is for how Y DNA is used in the ancestry parts of an ancestry dna test kit, for finding closer relatives.  If you are interested in Y DNA for ethnicity, please see the article in our ethnicity section.

YDNA ancestry DNA test kits can go further back

Most ancestry dna test kits do autoSomal testing as standard. However this DNA testing, gets weaker and weaker as you go back each generation.

It can normally match people up to 5 generations away.  Sometimes it manages people between 5 and 10 generations.

After 10 generations the DNA from each person is too weak to make a match.

YDNA testing hardly changes over thousands of years.

This means you can go back to ancient ancestors 50 to 60 000 years ago when the first humans were on earth .


How can YDNA go back that far

YDNA does not get diluted with each generation as it just comes from the father.

With normal autosomal DNA, it looks at your general DNA from both sides of your family, your mother and your father.

So you get half from your mother and half from your father.  This means that with each generation your DNA from each ancestor gets more and more diluted.

With parents you have half from each

With grandparents a quarter from each

With great grandparents an eight from each.

And so  on.

If you go back 10 generations there will be on average 1024 ancestors of that generation.

YDNA testing only looks at your father’s, father’s, father and so on.

Through the level of your family tree, it is a thin line going back into history.  As it is this thin line, not mixing with other people inn each generation, it does not get diluted with each generation.

Only one in each generation will be in the line, of your father’s, father’s, father’s, father’s, father’s, father’s, father’s, father’s, father’s, father’s, father.


How is YDNA useful in genealogy

Very often it can be hard to work out who an ancestor’s father is.  Records, documents and all other things on family tree websites are coming back blank.

YDNA is perfect for this as it looks at the father’s father.

As in Western countries the surname also comes from the father, it takes on an even stronger significance.   You can see if two families with the surname Smith are actually related.

With genealogy records a problem can be when two people have the same name.

It of course also taps into the possible issue that someone’s father, may not actually be the biological father.


YDNA shows an exact ancestor, even 10 generations back

We have seen earlier on that YDNA is a single strand of people going back through the generations.

This is because there can only be one father for a child.

This means that a genealogist can pinpoint an exact person in each generation, as that person is the father.

To make things simple and demonstrate this, let us give an example

Bob would like to know if he was descended from King Jim who is 6 generations back.  AutoSomal DNA can lead to results that do not prove this, because the DNA is so watered down with each generation.

As King Jim was famous and wealthy, he wants to know if he really is descended from King Jim.

There are 2 ways he can get YDNA to match up with King Jim:

1, By finding a male that Bob knows is descended from Jim he can test the DNA for a YDNA match.

Even autosomal DNA from this person of the same generation will not match, as this other male  is so far away related in the same generation.  They are many cousins sideways on the family tree, they really are 6th cousins as they are related by their great, great, great, great grandfather.

2, Another way to get YDNA from King Jim is to get DNA from his body in his grave. There have been occasions where universities have been able to dig up graves to get DNA samples, due to the merit of the case.

If there is a stage where a father only had female daughters, this will of course create a dead end though.


How can a female use Y DNA with an ancestry dna test kit, to find ancestors

The first thing to do is ask a blood relative who is a male, if they will do a test for you.  Such as a brother, father, uncle, or nephew.    If it is an uncle or nephew, they need to be from your father’s side of your family and not your mothers.

With autoSomal DNA, using a nephew who is a generation later is a disadvantage, however it is not with Y DNA in an ancestry test kit.   This is because of how autoSomal DNA gets 50% weaker with every generation.  As Y DNA hardly changes after 1000 years, it does not make much difference and this is what makes it so powerful.

You can even use a male who is further related, such as if you just share the same great great great grandparent.  This is 5 generations away and that would start to cause problems with an autoSomal ancestry dna test kit, but with Y DNA it is not problem.

It can happen though that someone in the chain never had a daughter, this means that the Y DNA was lost.  So it is important to find out if the ancestor you are looking for, comes from a line where there were males born in ever generation.

In genealogy DNA circles, this is called ‘daughtered out’.  Yes, genealogists can be a bit insensitive.

So for example, if your great great grandfather was called Bob and you are wanting to see if you are related to him. The following would cause him to be daughtered out:

  • Great grandfather did not have any sons, so the Y DNA was lost


  • Great grandfather had two children.  One was a son and one was a daughter.  However the son did not have any children.   The daughter had two sons, but of course the daughter did not carry through the Y DNA

The solution is to go back and back until you find an ancestor where the male line has kept going.   Using conventional DNA testing as well as genealogical records this is normally not too hard, but it is time and work.

If this is too much hard work and difficult, you could also hire a genealogist.  They can go through each generation to ensure the male line is in tact

As Y DNA is unchanged for so many generations there are no limits to how far back you can go.  However please do be cautious though that, with every generation you go back, there is a risk that someone’s father, is not the actual biological father.  This is where using general autoSomal dna testing as well as genealogical records can be helpful.


Convincing more distant male relatives to give you a sample for an ancestry dna test kit for you.

Then is the process of convincing people you know less well to help you.

Before starting them though, spend time having a friendly chat with the person, let them get to know you first.   It is a bit like dating, you get to know someone before asking them to marry you.

We recommend these tips:

1,  You do the work for them with organising it all, they just have to let you take a dna sample from them.  You will just turn up and take a sample.  They do not need to be involved with ordering the kit, sending off the sample, registering the kit, learning how to use it and so on.   They are given full access to anything they want to though, this is so they feel in control of their dna.

2, You tell and show you all that you have done so far.  This shows that it is real and genuine with the right intentions.   The best thing to do is show them about them and their own family.  Then they see what is in it for them.

3, If you are open and transparent about what you are doing and why, most people will help.

4, Agree they will get all the information from your research.  Also you could give them access to ancestry dna test kit portal.

5, Many people will not want the bother of logging into the site.   So also tell them they will get a full report from ancestry dna test kit and some other genealogical stuff helps seal the deal.  You will email or post these as it’s own document or files

6, Also telling them that they can share it with their family, or have more copies for their family, often helps.  People want to talk about and show off their family, also get their relatives interested in their family.

7, You will probably have to pay for it.  Any idea that they could be asked for money at any stage, could put people off.  People are of course wary of being tricked and being asked to pay money at a later stage.  To help get around this, try and talk about relatives you have in common, so they can ask around about you and find out if you are trustworthy.

Please do contact us with if you have done this and say what you learned, we would love to have more experiences to add to this guide.  Trying to get people involved is often a challenge.

What we do know is that if people are given the results about their family, they are normally loved, cherished and shown around.


Y DNA not part of all ancestry dna test kits

Y DNA is not part of every ancestry dna test kit.  The ones that do have it, either have it as part of their basic kit, or as an added extra.

Also there are limits to what each one uses it for.

Home DNA just use it to see your ethnicity in greater detail.

Living DNA does this and also uses it as part of matching you up to your relatives that may also be on their DNA database.

My Heritage that can integrate your results with the genealogy family tree records, also on their site, have Y DNA an optional extra.

The company Ancestry DNA , does not do Y DNA testing at all.

Please do look at our guide see the best ancestry dna test kit reviews for your needs.


How YDNA fits in with the other chromosomes

You have 23 chromosomes.

22 of these are the normal strands that you see in most diagrams of DNA.  These are the things that determine almost everything about you, such as your height, hair color and so on.

However the X and Y are seen as number 23.

The Y chromosome only has 59 million base pairs on. A base is a piece of genetic code, like the musical notes in a song, or letters in a book.  This makes it the shortest chromosome and can be seen in the bottom right of this diagram.

ydna chromsome karyotype


YDNA is a sex chromosome, it is different to the general chromosomes

YDNA looks at the Y Chromosome.

The X and Y are called a sex chromosome, because if you have a Y and X chromosome you will be a male.  If you have an X and X you will be a female.

Whereas normal chromosomes are strands with dna code laid out onto each strand.  The sex chromosomes are rings.

The Y Chromosome is really small, even smaller than the XDNA Chromosome that is also useful in an ancestry dna test kit.

Here is a picture of a YDNA chromosome, it is on the right of and touching the XDNA chromosome.

Later on we will refer to how they are touching.

ydna chromosome dna microscope

Even though the Y Chromosome is small, it still gives lots of useful information.

Only the son gets the Y Chromosome, as women do not get one.   Also it is almost unchanged from the father’s Y Chromosome.

This is what makes it a really good line of information going back into the past.

Of course if a father has a daughter and not a male child, then his YDNA will not be passed on to the next generation.



YDNA does not recombine

Regular DNA chromosomes are in pairs, one strand from the mother and one from the father.

The person uses about half of the DNA from the mother and half from the father

However YDNA just comes from the father, so there is not this second strand.

This means that YDNA does not pair or recombine.  There is nothing for it to pair or recombine with.

It can happen that the tips of the X and Y chromosomes touch and so recombine.  This can be seen in the microscopic picture of them above.  However these bits are not used in an genealogy, or haplogroup ethnicity dna test kit.

This means that the results of the YDNA test will truly be just that from the father.


The different ways of analysing Y DNA

Although Y DNA does not change much, normally for a 1000 years, there are still changes.

These are called mutations.  Mutations are just changes and are not necessary bad for a person’s health, it is just what happens.

Changes can just make someone different, they could of course also be an evolutionary improvement.

The tests available are due to this.  They are

1, Y STR which stands for Short Tandem Repeat. It analyses from 12 to 111 very short segments of Y DNA and covers the whole chromosome.  Sometimes it is analyses more than 111 segments.

2, Y SNP, which stands for Single Nucleotide Polymorpism.  This analyses from one to hundreds of single spots, going along the whole chromosome.

Like with most things, each has it’s advantage and disadvantage.


Y STR ancestry testing