Got a question about your DNA Portrait?

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Why are the bands in my DNA Portrait different sizes?

You may have noticed that some of your bands are thicker and darker, whereas others are thinner and lighter. A thicker, darker band does, as you might expect, mean that there is more DNA present, but this is not because you have more of that DNA in you!

The reason you sometimes have more DNA in one band and less in another is down to the technique we use to amplify your DNA in the first place. This technique is called polymerase chain reaction, more commonly shortened to PCR. It takes a very small amount of your DNA as a starting point, and it amplifies it again and again. More amplifications means more DNA at the end of the process! As the DNA is amplified in an exponential process (i.e. doubling each time), it is difficult to know exactly how much we will end up with – sometimes we get a bit more and sometimes a bit less, hence the difference in band sizes.

You can learn more about how PCR works here: http://learn.genetics.utah.edu/content/labs/pcr

There seems to be a faint band in my DNA Portrait that shouldn’t be there, does this mean you may have read my genotype wrong?

ghost band

Every now and then we get what we like to call ‘ghost bands’ in some DNA Portraits. These are very weak bands that can occasionally pop up seemingly at random. Essentially they represent another, unrelated region of your DNA that, perhaps due to a similarity to the target region, is amplified just a little. They make an interesting addition to your DNA Portrait!

We can mark something out as a ‘ghost’ band rather than a ‘real’ band as we use two completely different methods to determine your genotype, which are carried out on separate days and then cross-referenced to ensure accuracy. If they don’t match, or there is any ambiguity, we re-run everything from scratch. As a result, we are confident that we provide an extremely high level of accuracy in our genotyping, although we will gladly offer to re-test if you have any doubts at all.

Why are some of my bands straight whereas others are wavy?

Wavy bands are often due to minor inconsistencies in the gel-like block that your DNA is run through. Every gel-block is prepared and set by hand, sort of like making a jelly. As it is a natural substance prepared fresh each time, occasionally small areas of the gel will have a different density to the rest of the block, which can lead to an interesting ‘wavy’ effect once the DNA is passed through it. This is a common effect of hand rather than machine processing and one of the reasons your DNA Portrait will be absolutely unique!

 Why are some lanes ‘streaky’ whereas others are relatively clean?

The streakiness or ‘smearing’ you may see in some lanes of your DNA portrait is usually caused by the presence of high amounts of your original chromosomal DNA; in other words, all of the other DNA that we extracted from your DNA sample.



When we generate your unique DNA Portrait, we are aiming to amplify just one specific region of your DNA at a time (the one that relates to the trait of interest). To do this, we add a little of your DNA to each reaction to act as the template. If there is a lot of DNA template present, this can show up on the final image as a streak. In other words, that streak is the rest of your DNA, left over from the reaction!