22 April 2019

DNA Testing for Crimes by Twins

Science is on the verge of distinguishing between identical twins. Consider cases of crimes where DNA material leads not to one person, but two: identical twins. Until now, no one could say with certainty which twin might be guilty. Here's why.

Each twin comes from the same egg, split into two, creating two eggs with identical DNA. Old DNA testing was unable to distinguish between identical twins, but there are two fascinating options on the horizon that might just help.

The first difference between identical twins begins immediately. Although each is endowed with the same DNA - “When a fertilized egg starts dividing, there’s a small chance each new cell will gain a new mutation. When the cells separate into twin embryos, one gets some of the mutant cells and the other gets the rest. Unique mutations will end up in cells throughout each twin’s body.”

“Such a test would be difficult, then — but it would also be definitive. Just a single mutation, confirmed by multiple analyses, would be enough to implicate one twin and exonerate the other.”

“It’s not something that’s going to happen every day in every laboratory,” said Dr. Krawczak (a geneticist who now teaches at Kiel University in Germany). “But once people become aware of this, there may be a lot of cold cases that come back to life.”

However, this testing is in its infancy and is both expensive and time consuming.

The next set of DNA changes are called epigenetic changes and happen during embryonic development and continues for the rest of our lives.

Dia Rahman, a PhD student in Public Health at University of Waterloo has a special interest in social impacts on health and, therefore, is fascinated with epigenetics. “We are born with our DNA but what is impacted by the environment is the dance between active and inactive genes,” Dia says. “That is what is impacted by our upbringing and experiences. That is epigenetics.”

“A common analogy used to describe the epigenome is to consider genes as instruments in the “symphony” of life. But they don’t play themselves. They need musicians. Epigenetics would be the musicians that help express (or silence) the performance of our genes. Exercise, sleep, trauma, aging, stress, disease, and diet have all shown significant effects on the epigenome.”

Detecting epigenetic changes is faster and cheaper than looking for mutations. Graham Williams at the University of Huddersfield, UK, has found that epigenetic changes alter the melting point of DNA. “When the team heated up the twins’ DNA samples, they found the melting points were different – allowing them to tell the twins apart genetically. The test was also much quicker than whole genome sequencing, says Williams. “It can be done in just a few hours.”

So, essentially, we are born with our DNA - an entwined gift from our mother and father. This is not immutable. Some of our DNA can be altered by mutations. Parts of our DNA is also turned off and on by how our life impacts us. As our DNA testing improves, we can distinguish between identical twins.

Perhaps the most important part of all this has nothing to do with crime. It show that our DNA we once thought never changed is actually impacted by the life we live. And that is fascinating.


  1. That is fascinating, Mary.

    I've long suspected my brothers had low boiling points. Now I can prove it, although we're not twins. Young Leigh, junior mad scientist, built a fluoroscope. He X-rayed his youngest brother's skull. That may explain a few things later in life.

    Very helpful article, Mary.

  2. Fascinating, Mary. I've always wondered about how one could use DNA to figure out which twin "did it".

  3. Good information. This is a great twist for a story plot. Thanks for sharing.

  4. Great post, Mary - This would take care of a lot of the old "identical twin" plots.
    But it's also fascinating how life experiences change genes. I was amazed by the study about the WW2 famine in the Netherlands that showed that it actually changed the genome - and that change was handed down much further than anyone might think.

  5. That is amazing news! And then there are mirror twins, polar body or half-identical twins, chimeras ... the mind boggles.

  6. Leigh - LOL! A new plot - which sib melted the others?
    Paul - this testing is still in its infancy but fascinating.
    O'Neil - I picture a lab that tests and verifies and the need to convince others of this new tech!
    Eve - that is the part I still can't get my head around. How do these epigenetic changes get passed down generation to generation? Certainly stress changes DNA and makes people more likely to respond to stress with cortisol spikes - but how does that get passed down - creating a common narrative of an 'anxious' family trait??
    Elizabeth - totally!

  7. As an identical twin, I have said for years we have major difference. We spent the first 20 or so years listen to how much we were "identical" but into our mid to late 20s we realized the difference. A small amount of anesthesia will knock my sister our for hours, me I woke up too soon after surgery, twice...not fun. Medication, they have to cut hers in half and give me double. There are many other things like this that we've discovered over the years so it dosen't surprise me about the latest DNA news.


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