DNA testing plain and simple

DNA testing plain and simple guide

All I wanted to know, plain and simple, was: is DNA testing worth it, in relation to family history/ancestry?

‘Centri-Morgans,’ ‘FIRs’… but listening to a talk on DNA results, I was left thinking ‘maybe you need a scientific background to make sense of this stuff’. And a very specific one, at that. 

My humanities degree for sure doesn’t qualify me, but it does help me boil down a lot of jargon and technical detail into plain and simple English.

Key plain and simple points: what can DNA testing tell you?

Boiling it down, DNA testing results can tell you:

  1. Your ancestors, going back up to four or five generations. And wider family (distant cousins etc). Based on matches on databases.
  2. Your distant geographical origins – to a limited degree.

Quick plain and simple points

Here are some quick plain and simple points I noted as conclusions from the talk, and from researching DNA testing online.

Matches are only as good as the database you are looking at

The information about your ancestry available from DNA alone is limited. It relies on other people having done tests, and on matching people’s results up on databases to find connections. 

So, if all your distant cousins put their DNA test results on a different database from you, you won’t find each other.

Adoptions or foundlings

DNA tests matches may help you get answers as to your parentage. But there is no guarantee they will be happy ones.

Skeletons in the closet

Even in a ‘regular’ family, there may be surprises. Regular family history research can uncover illegitimacies, bigamists, other criminals. DNA results can show that at some point in time, ‘Daddy’ was actually the milkman.


Some hints on databases may be based on incorrect family trees. Ie, may point to someone who shouldn’t be on the tree.

Also, be aware that we don’t inherit exactly the same DNA from our parents as our siblings do. So if you and your sister do the same test, you won’t get identical results. She may have inherited a lot of Great-Great-Grandpa Smith’s DNA while you got almost none.

If your mother is also your aunty…

If a man married two sisters, or two brothers married two sisters, it mucks up the use of DNA to point to relationships.


If you are British, you are a mongrel, or a Heinz 57, if you’d rather. Go back far enough and our ancestors all came frome somewhere else: Romans, Angles, Saxons, Vikings, Normans.… They came, they saw, they conquered – and inter-bred with communities who were here before them. So if you want to know how many parts Viking you might be, or if the stories about someone settling here from Greece way back, go ahead with that mtDNA  test (see below).

However, the results are based on ‘clusters’ of people with similar DNA and should be treated with caution. Possibly a very large pinch of salt.

Privacy and ethics

DNA can be used for a lot more than genealogy. There are laws governing what the police can do with your DNA, and how long they can keep samples. If you are going to hand yours over to a private company, be sure you know what exactly you are agreeing to, regarding its usage.

As for ethics… if you find out something surprising, think very hard before sharing that information with someone else. Will they be happy? Or is their ignorance bliss?

All that science

Looking at a printout of someone’s results, I suspect very few people attempt to get their heads round it all. And instead, look to see if the database suggests matches with other people. However, you do need to know about the three types of DNA testing available.

Types of DNA testing

Autosomal DNA tests

These trace a person’s autosomal chromosomes, which contain the segments of DNA the person shares with everyone to whom they’re related (maternally and paternally, both directly and indirectly).

This is what sites like Ancestry use. 

It is only any use for going back five or six generations, at most.

Y-DNA tests

These are for men only, and trace the patrilineal (male-line), only. If you are a man and only interested in your literal forefathers, this may be for you. However, don’t forget that your direct paternal line is a pretty small part of who you are. For example, you have 128 great-great-great-great-great grandparents, of whom 127 are not your direct paternal line.

mtDNA tests

Mitochondrial DNA tests trace people’s matrilineal (mother-line) ancestry through their mitochondria, which are passed from mothers to their children.

Men and women can take the test, but the results are the female line only. They do show ‘ancient history’, but that seems to be in general terms.

As I understand it, that means it may show you share a connection with someone from the Middle Ages, but only in a pretty vague way. And if you share a full mtDNA sequence with someone, your common matrilineal ancestor could be from the 1800s – or the 1300s.

Will I bother?



Ok, that’s ‘plain and simple,’ but it would be helpful to explain my decision!

I have traced most lines of my family tree back at least several more generations than autosomal DNA testing can.

Through my research, I have discovered second and third cousins around the world. And through family history societies, and ‘message’ options on sites like Ancestry, I have got to know some of them. And met people from/in other countries.

In short, I don’t think DNA testing could tell me anything I haven’t or can’t find out other ways. 

I don’t care if I am X parts Norman, or whatever. Even if those results were 100 per cent reliable, which they aren’t.

Nor do I care if somewhere up the line, a person I think was a several-times great-grandfather wasn’t because my several-times-great-grandmother had an affair. Anyone can be a biological parent: it’s the people who bring you a child and care for them that matter.