Understanding DNA

For as long as I can remember, people have asked me if I was partly Chinese. When I was a child, people would sometimes say they hadn’t spoken to me, because they weren’t sure if I spoke English. When, more recently, we visited China, I had complete strangers approach me in shops, telling me that they could tell I was ‘half-Chinese’.

Both my parents are English.

However, I thought that probably, way back in time, I must have a Chinese ancestor somewhere. I therefore decided I would quite like to do one of those online family-tree-research DNA tests. For Christmas, Husband kindly bought me an Ancestry DNA kit.

I was expecting my DNA results to come back as mainly English/European, with perhaps 1 or 2% Asian. Doing the test was very easy – I had to spit into a tube, add stabiliser, and post it in the small white box provided. I then had to wait (about 6 weeks, but it felt much longer).

The whole process did rather spark an interest in DNA, and how exactly these tests work. So I began to do a little research, and I found that many of the explanations online (including those written by the ancestry websites) are rather misleading, so I thought I would explain it to you. I had help – my own knowledge stops at A’ Level Biology  many, many, years ago. However, my children work with people who study DNA, so they were able to answer my questions.

DNA stands for ‘deoxyribonucleic acid’ (you will never need to know this outside of exams and pub quizzes). It’s a long string of ‘stuff’ that carries all the instructions (genes) for how you are built (Eg. whether you’ll have blue eyes or brown eyes). You get DNA from your parents – half from your mum and half from your dad. These strings of ‘stuff’ form two strands, and when cells reproduce, you get one strand from each parent. (There is something different, called ‘mitochondrial DNA’. This is the DNA found in the mitochondria – the ‘powerhouse’ of the cell – and this passes ONLY DNA from the mother. Which means it never changes, and they can discover things about your ancestry from thousands of years ago. But we’re not talking about that type.)

Now, lots of the articles online are rather misleading, as they tell you that you receive half your DNA from each parent, which means, for example, that you and your siblings might have different DNA. This is sort of true, and is all you need to know for GCSE biology. However, it doesn’t take into account something called recombination. All of these articles are therefore misleading. They imply that siblings can have vastly different DNA (so even if your brother has paid to test his DNA, you should too, because it might be different) – remember, these companies are selling tests, it is not in their interests to tell you that the variations will be tiny.

They completely omit recombination, which happens two or three times on every chromosome (other than the gender one in which it only happens for XX). What it means is, you don’t actually inherit one of two potential chromosomes from your mum. You inherit a chromosome that is a mix of the two.

Here is a simple example to explain how it works : Imagine Mummy has two sticks of playdough – one red and one yellow. Daddy also has two – one blue and one green.

According to the online articles (and GCSE biology) both parents give Bob one colour each. So he could, for example, have one red and one blue.

But in reality, before you each choose which colour to give to Bob, you snap the ends off each of them and swap them round.
So in reality Mummy would give Bob one that was mostly red but with some yellow blobs, and Daddy would give him one that was mostly blue but with lots of green blobs. That means you always show traces of everything.

The DNA companies send two results. One shows where your ancestors came from. This is because certain races have certain kinds of DNA, and they can see the markers when they process your DNA. If a group has not, in the past, mixed very much with other races, then the markers are very clear. Due to recombination, the ethnic markers found in your DNA are likely to be very accurate, and will not differ much between siblings with the same parents. So, depending on the markers found, you might be told you are “5% European” and your brother might have clearer markers, and be told he is “5% Spanish” (which is not, really, different). The company can only define certain markers – I understand that they have not identified many markers yet within Asia, so people will not necessarily discover whether their ancestors were Chinese, Korean or Japanese, and might simply be told “9% Asian”.

The company also tells you what percentage of that race you are – such as 30% Asian. The percentages, because they are based on ethnic markers and not actual DNA, can be very inaccurate. So, 30% Asian means you have Asian ancestors, but maybe it was a grandparent, maybe a great, great, grandparent.

However, my results showed that actually, I have no Asian blood at all – which was a little disappointing.

I hope you are happy with who you are.
Thank you for reading. Take care.
Love, Anne x

Anne E. Thompson has written several novels. They are available from bookshops and Amazon.
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