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What’s an Electropherogram?

In this video, Dr Gavin Turbett discusses what is an electropherogram and how is it interpreted.
So, this is the raw data and we call it an Electropherogram or EPG. This is the raw data, and it’s not easy to read in this format. So, to make it easier to visualize, the scientists will use software to display the information differently, and you can see here we’ve got all those different peaks. There’s four colors - there’s blue, green, there’s black and red. Now they get spread out into the different colors to make things easier to read, and you can still see those same peaks. But underneath that, you can also see now those squares with information written inside.
That is information about - what allele has been called, as well as the height of each peak, and this, as I said, is typically the way that a DNA profile or an electrocardiogram would be shown within the laboratory. So, we’re now zooming in on a part of that on the blue channel, and you can see in that green bar sort of that runs across the top, there is some names. There is AM, the rest is cut off, but that’s called Amelogenin, and that is the marker that lets us determine the gender. The other markers, there you can see are D3S1358, D1S1656, D6S1043 and so on. So those names like D3S1358, They are the loci.
They are the loci that are being tested and it is the blue peaks that are the results. They are the alleles for that particular person. So, the forensic test kit will always, this particular kit, PowerPlex 21 will always test exactly the same loci but the results, the alleles will vary from one person to the next. So, forensic scientists will use specialized software that will help them to interpret this data. It can be done manually but as as DNA test kits have got more complex, it is easier and safer to use specialized software. So, you can see here now the software has gone through and interpreted each allele.
So, you can see there on the left, there is the allele X and allele Y. The peak heights are given just below them, and then, as I said that, because we’ve seen both X and Y chromosomes, it tells us that this particular sample is from a male. The next locus D3S1358, we can see it is detected alleles 17 and 18. For D1S1656, so D1S1656 is the locus and the alleles that have been detected at that locus are 12 and 13. Then at D5, we see alleles 12 and 20 and so on.
Now, here I’m showing the green dye channel, it’s a bit more of the same DNA profile from the same individual person, and this time, the loci the names are D16S539, D18S51 and so on. Now you’ll see again, there are two alleles at each locus, except you’ll see at the fourth locus CSF1PO, there is actually only one allele present an allele 12. Now, in actual fact, that person does have two alleles. They just happen to have inherited two alleles that are of exactly the same size. This person has inherited an allele 12 from their biological mother, and they also inherited an allele 12 from their biological father.
Because the alleles, they are both the same size, they just simply, of course, stack on top of each other and appear as one peak. So, when there are two alleles, we say that the person is heterozygous at that locus and where they are only have one allele as they do for CSF1PO, we say that the person is homozygous for that locus, and this is perfectly normal. There is nothing at all that is unusual about this. It is perfectly normal for people to be heterozygous at some loci and homozygous at others.

While dealing with DNA evidence, you may come across the term ‘electropherogram’ or ‘EPG’. What are electropherograms and how are they interpreted? Watch Dr Turbett explain different parts of an electropherogram in this video.

In your jurisdiction, are electropherograms submitted along with DNA reports? Have you ever asked for them in your casework? Share with us in the comments below.

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Decoding Forensics for Legal Professionals

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