Category Archives: DNA

Father’s Unborn Twin Is the Genetic “Father” of His Son

A couple of years ago a happy couple in Washington welcomed a new baby boy. All was good until a paternity test showed that the father was not the father. Uh-oh. Well, it’s not really that bad. Turns out that genetic testing revealed the father was a chimera and the genetic testing was confused by his unborn twin’s DNA, which the father had absorbed in utero. Chimerism is an odd and interesting medical entity.


Greek Chimera

In Greek Mythology, the Chimera was a fire-breathing female that was part lion, part goat, and part dragon. Fortunately, human chimeras, which result from the combining of two or more human embryos in utero, are typically normal in every way—-except for that DNA stuff.

I’ve blogged and had Guest Bloggers comment on chimeras before:

Q&A: How Could My Sleuth Recognize a Chimera?

Guest Blogger: EE Giorgi: I Am My Mother’s Chimera. Chances Are, So Are You

Guest Blogger: Human Chimerism: Mindboggling DNA Tests Gone Wrong


Can a DNA Sample Reveal Age?


DNA found at crime scenes can be extremely useful in identifying a perpetrator. But this only works if they have a known suspect and a DNA sample from that suspect, or if the perpetrator is in the national DNA database—-CODIS. Without something to compare the crime scene DNA sample against, DNA is not very useful. Same can be said for fingerprints. But perhaps DNA offers something else.

Employing DNA obtained from a crime scene, Familial DNA has been used to narrow the list of potential suspects and this has proven useful in many cases—such as the famous Grim Sleeper serial killer. I have blogged on this before in cases such as The Boston Strangler and the amazing case of Yara Gambirasio.

DNA will of course reveal gender, but there is also research suggesting that race, hair and eye color, and physical features such as stature might also be determined from a DNA sample. These aren’t completely worked out yet but they are intriguing aspects of DNA analysis.

But what if a DNA sample could be used to determine the approximate age of the person? This would definitely help as, once again, it would narrow the suspect list. For example, if the crime scene DNA could be shown to have come from someone who was approximately 25 years old it would effectively eliminate a 60-year-old suspect. But is this possible? Maybe.

A new approach, using a process of gene expression called methylation, seems to offer hope. Researchers at the KU Leuven University in Belgium have developed a technique for assessing the degree of methylation in a DNA sample. They believe that this analysis will narrow the age range of the individual down to a four or five year window. If this proves to be true, law enforcement will have another useful forensic science tool.


Even Identical Twins Have Different DNA

For years the dogma was that identical twins possessed DNA profiles that were not distinguishable from one another. But things are changing.

Fraternal (dizygotic) twins come from two eggs and two sperm and are as different as if born years apart. They are twins solely because they shared the mother’s womb at the same time. But, identical twins (monozygotic) come from a single egg and sperm. They are formed when the fertilized egg undergoes its first division and the two new daughter cells move apart, each then proceeding to form a separate individual. Since they came from the same fertilized egg, the share the same DNA. In fact, the two would be indistinguishable by standard PCR-STR DNA Profiling.




But, in reality, even identical twins have distinct DNA. We just weren’t able to see the differences. Before now.

As each twin embryo grows and develops in utero, and the cells continue to multiply, the replication (copying) of each twin’s DNA isn’t perfect. Minor errors or variations begin to appear so that by birth each Twin’s DNA is slightly different from its sibling. And as life goes on, each twin is subjected to different environmental stresses, which is turn alters each one’s DNA replication.

As opposed to STR, which looks at repeating short sequences of bases within the DNA strand, a newer DNA technique, known as Single Nucleotide Polymorphism (SNP), gives the examiner a complete DNA sequence of the strand being analyzed. That is the exact sequence of bases in each strand is determined and this can reveal the differences in the DNA of identical twins. Another newer technique known as High Resolution Melt Curve Analysis (HRMA) might offer still another method to make this distinction.

So even identical twins are not so identical.

Want to know more about DNA profiling? Check out the updated 2nd Edition of FORENSICS FOR DUMMIES.


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Posted by on May 2, 2016 in DNA, Uncategorized


Guest Blogger: Lisa Black: Everything Old Is New Again


My character, Cleveland forensic specialist Maggie Gardner, is unrealistic in one respect—she still spends a lot of time at her microscope looking at tiny bits of trace evidence, hairs, fibers, paint, and glass.

No one does that any more. Well, maybe Abby on NCIS, but she’s the most unrealistic forensic person on screen, even though she’s so cute we don’t care.

Sure, on old episodes of Dragnet you can see some nerdy guy in a lab coat explain how these pollen spores are only found in one quadrant of the city, but that art had already died before I started in forensics in 1994. We got spoiled by DNA, by ‘absolutely yes’ or ‘absolutely no’ answers. No one wanted to hear that this red nylon was ‘consistent with’ the suspect’s shirt, because they wouldn’t be hearing how many red nylon shirts were manufactured, how many were sold in this area, and while we’re at it let’s hack into Macy’s sales figures and find out who they were sold to. Unlike television, forensic labs do not have databases of all this information and would probably be violating a few important laws if they did. Nope, ‘consistent with’ was all you got. Take it or leave it.




They left it. Microscopic analysis became more or less a thing of the past. Forensic techs today wouldn’t recognize a pollen spore or know what to do with it if they did. Fibers are ignored. Hairs are examined only to screen out candidates for, well, DNA.

Imagine my surprise, then, when I peruse the latest Journal of Forensic Sciences and stumble on an article about using something called palynological scanning to rapidly evaluate suspect and victim testimony.




Palynology, it turns out, is a fancy name for…pollen. Pollen and spores and other ‘microscopic entities’ of trees, shrubs and herbs. No hairs, fibers or paint, but you get the idea. This analysis proved useful in some cases of rape or assault, in situations where the victim and suspect both contacted the ground and pieces of the ambient flora could attach to their clothing.




In one case the suspect said he and his victim engaged on a lawn behind a public building. The victim said he attacked in a heavily wooded area, the spot surrounded by beech, birch and sycamore trees. Each site had a distinct mix of items—palynomorphs– with complicated Latin names. The suspect didn’t deny that he had made contact with the victim so willingly gave up the clothing he’d been wearing at the time, and sure enough, all those little palynomorphs indicated that he had been in the woods and not on the lawn. This did not prove that he had committed the crime. It only proved that he had lied about the sequence of events, and that was sufficient to prompt a confession. Otherwise this case would have languished in an eternal hell of ‘he said vs. she said.’

Of course had this guy listened to legal counsel before he made a statement, he probably would have figured out to come up with an alternative, and innocent, reason to have been rolling on the ground near the crime scene, and all these spores would have been for naught. As it is, surely the defense will bring out statistics regarding the vast number of beech and sycamore trees in the area, perhaps in the suspect’s own neighborhood, and the idea that maybe he had been doing some gardening earlier in the week in that same pair of pants. This is why things like pollen analysis fell out of favor with the courts…but the spores are still out there, voluminous, distinct and quite concrete little buggers that will stick in all sorts of places one might wish they wouldn’t. So are hairs, fibers, and paint. Maybe ‘consistent with’ is all you can get out of them. But maybe, sometimes, that’s enough.

So in my books Maggie still looks at all this stuff because it’s more visible and visceral than yet one more DNA sample. Let’s face it—you’ve seen one cotton swab, you’ve seen them all. Bright clothing fibers are much more entertaining.

And this trace evidence will lead her down a number of roads—some of which, it turns out, she’d be better off avoiding.

Wiltshire et al. “A Rapid and Efficient Method for Evaluation of Suspect Testimony: Palynological Screening.” Journal of Forensic Sciences, Vol. 60, #6, Nov 2015, pp 1441-1450.


L Black

Lisa Black has spent over 20 years in forensic science, first at the coroner’s office in Cleveland Ohio and now as a certified latent print examiner and CSI at a Florida police dept. Her books have been translated into 6 languages, one reached the NYT Bestseller’s List and one has been optioned for film and a possible TV series.

Lisa’s Website:


that darkness cover


Hello! Just a quick note to let you know that my new book, That Darkness, is now available wherever books are sold!

It seemed like a typical week for crime scene specialist Maggie Gardiner–a gang boss shot in an alley, a lost girl draped over an ancient grave, a human trafficker dumped in the river–nothing all that out of the ordinary for the Cleveland police department as spring turns toward summer along the Erie banks. The methods are usual, the victims unsurprising–but when she notices a pattern, a tenuous similarity among the cases, she begins to realize that her days will never be typical again. How much of her life, her career, her friends, will she be willing to risk to do what’s right?

Jack Renner is a killer who does not kill for any of the conventional reasons…no mania, no personal demons. He simply wants to make the world a safer place. He doesn’t think of himself as a dangerous person–but he can’t let anyone stop him. Not even someone as well-meaning as Maggie Gardiner.

Maggie has the self-sufficiency of a born bit-of-a-loner. She works with a bevy of clever experts surrounded by armed police officers. She is both street smart and book smart, having seen the worst the city has to offer.

But Maggie Gardiner is not safe. And, until she can draw Jack Renner into the light, neither is anyone else.

Jeff Lindsay, author of the Dexter series, says: “Lisa Black always delivers authentic characters in riveting stories. That Darkness takes things to a spellbinding new level with a taut and haunting story that will stay with you long after you finish reading it.”

Publisher’s Weekly says: “The intriguing forensic details help drive the plot to its satisfying conclusion.”

“Black is one of the best writers of the world of forensics, and her latest introduces Maggie Gardiner, who works for the Cleveland Police Department. Her relentless pursuit of answers in a dark world of violence is both inspiring and riveting. Readers who enjoy insight into a world from an expert in the field should look no further than Black. Although Cornwell is better known, Black deserves more attention for her skillful writing – and hopefully this will be her breakout book.”– RT Book Reviews, 4 Stars (Top Pick)


Guest Blogger: Megan Inslee: My Love-Hate Relationship with Forensic DNA



What is the most important point to keep in mind when working with forensic DNA evidence?  There are probably a lot of answers to that question, depending on your experience and perspective.  I’ll let you in on my opinion for now, as a former DNA forensic scientist. One of the imperatives of working forensic DNA cases in this modern age is this: accepting that there are cases (many, in fact) that DNA can’t resolve.

Almost every time I testify, I’m asked “why might you not find DNA?” This is a good question, one which I usually answer with a fairly long list of possibilities, but it all boils down to three main points. 1. DNA may not have been deposited in the first place. Does this mean that the incident didn’t happen as reported by the victim or witnesses? Not necessarily – more on that a bit later.   2. Maybe too little DNA was deposited for the lab to test and identify. But can’t you guys detect even a few cells? More on that, later, too.  Or, 3. Perhaps DNA was deposited at an adequate level, but much of it was washed away or degraded over time. I saw a special on cold cases solved by DNA decades later – I don’t believe there’s anything you can’t do. Well, keep reading.

1. DNA may not have been deposited in the first place.

We’ve become so accustomed to DNA evidence being presented in criminal justice cases that we seem to need to take a collective step back to reflect on a case in which it just isn’t there.  It really depends on the scenario and the knowns of the case what this lack of DNA on an evidence item could mean.

The murderer doesn’t always cut herself on the knife and leave drops of her blood at the scene. The burglar may have kept his gloves on throughout the entire crime, never touching anything with a bare hand.  A child molester doesn’t always leave semen evidence for us to test.

And, of course, DNA may not be present on a tested evidence item simply because the scenario didn’t unfold the way investigators believed or the witnesses stated or the victim recalled.  Corroborating DNA evidence with reported scenarios is a tricky business, one which doesn’t always result in a resolution tied up with a big red bow.

2. Maybe too little DNA was deposited for the lab to test and identify.

Remember the days when crime labs couldn’t get DNA from anything smaller than a blood drop the size of a quarter?  And remember when, even when they started getting DNA from smaller samples, the odds of someone else having the same DNA profile was only one in several thousand?  Well, I don’t – that was before my time.

But I was there for the early years of the current DNA typing technology, Short Tandem Repeats (STRs). Those were the days in which we tested mainly blood, semen, and saliva.  We had a good idea of what we could and couldn’t get results from and we ended up with a lot of single-source DNA profiles.  These result in straight forward comparisons to reference samples which yield either an exclusion, if the profiles don’t match, or a match.  In the case of a match, we calculate and issue some crazy-big statistic that illustrates to the reader (the investigator or attorney or juror) just how significant this match is (spoiler alert: the number is often in the quadrillions – matches are pretty darn significant).  And as great as this is and was, the criminal justice system wanted (and in many cases, needed) more.

Science over time, I’ve found, rarely disappoints.  The techniques and products that result from years of experimentation, trial and error, grant funding and academic research end up being a culmination of the best approach among many.

Instead of changing the sites we used for forensic DNA typing, researchers found that we could extract and clean up the DNA a little better and attain higher sensitivity.  They modified the primers and added a few more.  They improved the reagents that we used to get our profiles and made them a little more robust. They made instruments that could automate sample processing so that we could do more samples in less time.  All of this has led to higher throughput and more sensitive results.

Currently, scientists are not just attempting to get DNA profiles from well-defined body fluid stains, as before, but also from areas of evidence items that have tested faintly positive for a body fluid. They are swabbing areas of items that someone in the case may have touched.  These types of samples have much, much fewer cells than, say, a fat drop of blood.  And, while significant to the case and incident at hand, these samples are likely to contain not only very few cells, but mixtures of more than one person’s DNA, further complicating the analysis.

3. Perhaps DNA was deposited at an adequate level, but much of it was washed away or degraded over time. 

It’s important to remember that DNA is a molecule, one with millions of parts.  Cells must be intact in order to properly preserve the DNA.  And hundreds of cells must be present in a sample in order to obtain a decent profile for comparison. Wiping or washing a surface can remove cells. Environmental factors such as heat, UV light, or bacteria can break cells open, exposing DNA and ultimately breaking it down.

Also, it’s useful to know that the laboratory process, itself, is lengthy, requiring many phases, none of which perfectly preserve all of the DNA in the sample from one step to the next.  If I detect 200 cells in a sample in the lab, it doesn’t mean that 200 cells were originally deposited on the evidence item at the time of the crime.  Even in the best evidence-preservation scenario, there is loss of genetic material on the crime-scene-through-laboratory-testing journey.

In the end, as much as I love forensic DNA (and I hope you do, too), it’s important to keep its limitations in perspective in every case. The presence of DNA evidence does not prove guilt. The absence of DNA evidence does not prove innocence. The current state of forensic DNA technology is, however, amazing! I think we can all relish in that without abandoning our role as critical thinkers.


Megan Inslee spent 13 years as a DNA forensic scientist in Washington State.  She has her Bachelor’s in Biology as well as her Master’s in the Genetics track of Laboratory Medicine from the University of Washington. She currently resides on an island outside of Seattle with her husband and three small children, writing technical documents, preparing grant proposals, and providing consultation on a freelance basis.


Posted by on March 29, 2016 in DNA, Guest Blogger, Uncategorized


Dirty DNA



One truth in forensic DNA testing is that you must have a sample to test. That, of course, should be self-evident. But sometimes crime scene DNA isn’t readily available. There are no blood or semen stains on the floor or bed sheets or any location where they could be easily sampled. What’s the crime lab to do?

New methods are under development that allow for extracting useable DNA from some unusual places, even dirt. GEMBE (gradient elution moving boundary electrophoresis) grabs DNA hidden in the dirt by employing a molecular “tug-of-war.” Cool.

For more about DNA sampling and testing, grab a copy of my updated, 2nd Edition of FORENSICS FOR DUMMIES.

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Forensics For Dummies Updated 2nd Edition is now available.

Get it through your local Indie Bookstore or here:



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