Paternity testing explained – what are DNA markers and how can they tell us who a child’s father is?

Paternity testing explained – what are DNA markers and how can they tell us who a child’s father is?

As a DNA testing laboratory, we are often asked how a paternity DNA test can prove who a child’s father is.  

Whether you’re trying to find the best paternity test for you, or are simply curious about the science, you may want to know more about how paternity DNA tests are performed and how we can find out whether individuals are related simply by looking at their DNA.  

Here, we’re getting back to basics to give you a better understanding of how a relationship DNA test works and what makes an AlphaBiolabs paternity test the most accurate on the market.

The building blocks of DNA

Every human being is born with a DNA profile that is completely unique to them (except for identical twins, who share the same genetic material).

Each person inherits half of their genetic material from each of their parents, with mum and dad each passing half of their DNA profile to their children.

These profiles make up the building blocks of a person’s DNA.

In the laboratory, it is possible for DNA scientists to analyse the DNA of an individual and identify where a person shares matching ‘building blocks’ – alleles – with one or more people.

DNA markers that are shared between the tested individuals can determine whether they are related.

What are loci?

If you’ve been shopping around for a paternity test, you may have noticed that many testing laboratories will talk about the number of loci analysed within the cost of the test.  

Loci is in fact the scientific term for the locations of DNA markers within a strand of DNA.

In simple terms, think of a locus (plural loci) as a genetic street address of a DNA marker within the DNA strand.

Because loci are located on chromosomes and we inherit one chromosome from each of our parents, each locus (location in the DNA strand) is home to two alleles (one from each parent).

An AlphaBiolabs DNA test analyses up to 45 DNA markers (loci) – double the industry standard – to determine whether two or more people are biologically related.

The more matching DNA markers we can find, the more likely it is that the individuals are related.

How can we find out who a child’s father is using a paternity test?

Now that you know how DNA can tell us who a child’s father is, here’s an example of how a paternity test works in practice (if testing one child and one alleged father):

  • Cheek (buccal) swabs are used to collect cheek cell DNA from the man and the child.
  • These samples are sent to AlphaBiolabs’ DNA laboratory for analysis by expert geneticists.
  • Both samples are analysed and compared to one another. Our laboratory scientists will identify the alleles of up to 45 DNA markers (loci) within a strand of DNA and compare to find out how many matching DNA markers the man and the child share.
  • If the man is the biological father of the child, both the man and the child will share DNA at every marker tested to confirm a biological relationship.
  • If they do not share alleles at every tested DNA marker, it is unlikely the man is the biological father of the child.

While many testing laboratories like to market their DNA tests as the best and most accurate, an AlphaBiolabs paternity test analyses more DNA markers than any paternity test currently available on the market, making our paternity tests (and other relationship DNA tests) the most accurate and conclusive.

The more DNA markers we can match, the more conclusive the proof that individuals are likely to be related.

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Can an AlphaBiolabs DNA test look at a person’s genes?

An important thing to understand is that the area of DNA we are testing cannot tell us anything about a person’s physical characteristics such as their eye or hair colour, or whether they have any genetic health issues.

Instead, our DNA tests look at Short Tandem Repeats (STRs) that are in an area of the genome known as non-coding or ‘junk’ DNA.

Within these STRs are short fragments of DNA which are repeated in a defined location within a chromosome.

When we’re doing a DNA test, AlphaBiolabs’ expert geneticists will look for variations in the number of repeats (alleles). Related people will have identical numbers of repeats.

Where can I buy a paternity test?

Now you know how a paternity DNA test works, you can choose to order the UK’s fastest, most accurate paternity test from AlphaBiolabs.

We are the only testing laboratory in the UK to guarantee paternity test results either the same day (£169) or the next day (£99).

We also analyse up to 45 DNA markers (loci), for the most conclusive test on the market.

To order a paternity test or find out more, call our friendly and discreet Customer Services team on 0333 600 1300 or email

Order a DNA Test

AlphaBiolabs is an award-winning DNA testing lab. DNA testing starts from just £99.