RSS

Category Archives: DNA

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

For years now the concept of a “genetic chimera” has sparked the imagination of writers: from Stephen King to Michael Crichton, from CSI to The Office. The idea that an individual could harbor his/her own twin is creepy and intriguing at the same time, not to mention it offers the perfect escape from DNA testing in a police procedural plot.

But if you think that “chimeras have been done already,” think again. All fictional works written so far have exploited the concept of tetragametic chimeras, which results from combining two or more genetically distinct organisms. In humans, this happens when two fertilized eggs fuse together during the first hours of life in the womb.

Yet Mother Nature has invented many other forms of chimerism.

Some genetic defects/mutations can lead to individuals with genetically distinct cells in their body. Usually these defects involve anomalies in the number of chromosomes, but there are also asymptomatic cases, like for example animals whose coat is a patchwork of different colors, as in tortoiseshell cats. This type of chimerism is called mosaicism. Contrary to tetragametic chimeras, which originate from two or more individuals fused together, mosaics originate from a single individual. People whose eyes have different colors are also an example of genetic mosaicism.

Tortoiseshell cat (Source: Wikipedia)

Tortoiseshell cat (Source: Wikipedia)

 

Scientists claim that chimeras are much more common than we think. Chances are, you could be your own twin. But how surprised would you be if I told you that you are actually far more likely to be your mother’s chimera than your unborn sibling’s?

“Microchimerism refers to a small number of cells (or DNA) harbored by one individual that originated in a genetically different individual” (Gammill and Nelson, 2010).

An individual receiving a donor transplant or a blood transfusion is an example of microchimerism. Yet the most common form of microchimerism happens during pregnancy. There’s an ongoing two-way cell trafficking across the placenta, and these exchange cells can actually proliferate long term in the host’s body: fetal cells can be found in the mother years after she gave birth. In fact, because even spontaneous abortions cause fetal cells to be released into the mother’s body, women who became pregnant but never gave birth can also harbor this form of microchimerism.

Mystery writers are familiar with the “Jane Doe scenario”: an unidentified woman that lands on the medical examiner’s table. One of the many things the ME can learn about this woman with today’s technology is whether or not she was ever pregnant—even if the pregnancy ended with a spontaneous abortion. With a single test the ME can find male DNA in Jane Doe and deduce that at some point she was pregnant with a baby boy. A baby girl can also be detected, but it requires more than one test.

Just like fetal cells can be found in the mother years after she has given birth, the inverse is also true: maternal cells have been found in fetal liver, lung, heart, thymus, spleen, adrenal, kidney, pancreas, brain, and gonads. What’s surprising is that in either case (mother-to-fetus transfer, or, vice versa, fetus-to-mother transfer), the extraneous cells migrate to a certain tissue and, once there, they are able to differentiate and proliferate, acting at all effects as if they were engrafted. One paper found circulating maternal cells in 39% of the study subjects (Loubiere et al. 2006).

But even if you are not your own twin, even if you don’t harbor cells from your mother or your child, even then chimeras are closer than you think. Because we all originated from a chimera: roughly 10% of our DNA is made from viral genes, and how this came to happen is a fascinating story.

A long time ago a virus infected a sperm cell or oocyte of one of our ancestors. Once there, the genetic material from the virus fused with the genetic material of the cell —- that’s an old trick viruses play so they can replicate. Except this particular virus never replicated. The sperm or oocyte was fertilized and became a fetus, and that fetus now carried the bit of viral DNA. The viral genes were “stuck”, no longer able to replicate, and thus effectively silenced.

Finally, the last form of chimerism I would like to discuss is far less known because it belongs to a fairly new field: epigenetics.

Genes are packaged inside the nucleus, some deeply hidden inside, and some exposed so that they can be easily “translated” into proteins. This configuration can change in time, as genes can move from the inside of the nucleus and become exposed, while others previously exposed can become hidden. Life events, changes in the environment or in diet, stress, and traumas can potentially affect these mechanisms, causing some genes to turn on while turning off others.

Epigenetics is the study of all mechanisms that can affect gene silencing (turning the genes “off”) and gene expression (turning the genes “on”). In other words, it addresses the question: what causes some genes to shift from being hidden (silenced) to becoming suddenly exposed (expressed) and other genes instead to suddenly become hidden (silenced)?

The amazing thing is that these epigenetic mechanisms are not encoded in the DNA, yet there have been studies that have shown that epigenetic changes caused by stress or diet can indeed be carried over for the next two-three generations.

You’ve probably guessed it by now: an individual whose cells express distinct genes within the same tissue is called an epigenetic chimera.

From a writer’s point of view, this kind of chimerism lends itself to many more scenarios than the genetic one. For one thing, it is much more complicated to detect as the defects no longer lie in the genes themselves, but rather in which genes are expressed and which aren’t. At the same time, epigenetic disorders can give rise to any sort of dysfunctional phenotypes. And you have a wide range of “life events” that could potentially trigger the “sudden change” in your character(s): viruses can certainly mess up with the cells’ signaling and turn on forgotten genes; an accident or physical trauma can spike new sensations/symptoms (have you ever heard of someone’s sense of smell suddenly spiking after a car accident?); a change in diet/environment; etc.

Vampires and zombies may have been done already. But there’s still a lot of room for chimeras of all kinds.

 

EEGiorgi

EEGiorgi

 

E.E. Giorgi is a scientist, a writer and a photographer. She loves to blog about science for the curious mind, especially the kind that sparks fantastic premises and engaging stories. She has done scientific consultations for writers such as Autumn Kalquist (Legacy Code) and bestselling author Carol Cassella (Oxygen). E.E.’s detective thriller CHIMERAS, a hard-boiled police procedural with a genetic twist, is now available on Amazon.

Link to Blog: http://chimerasthebooks.blogspot.com/

Link to book on Amazon: http://www.amazon.com/dp/B00JI6UNPE

Chimeras Cover

Previous Posts on Chimerism:

 

Q&A: How Could My Sleuth Recognize a Chimera?: http://writersforensicsblog.wordpress.com/2010/07/05/qa-how-could-my-sleuth-recognize-a-chimera/

Organ Creation and Harvesting: Reality Imitating Art: http://writersforensicsblog.wordpress.com/2013/07/18/organ-creation-and-harvesting-reality-imitating-art/

Guest Blogger: Elena Giorgi: Deep DNA Sequencing: http://writersforensicsblog.wordpress.com/2011/09/22/guest-blogger-elena-giorgi-deep-dna-sequencing/

Human Chimerism: Mindboggling DNA Tests Gone Wrong-Guest Blogger: http://writersforensicsblog.wordpress.com/2010/06/24/human-chimerism-mindboggling-dna-tests-gone-wrong-guest-blogger/

 
 

Cat DNA Solves Another Homicide

TINKER

TINKER

 

Tinker doesn’t look like a snitch. But then again, neither did Snowball. Snowball is a very famous cat. It was Snowball’s DNA that led to the solution of a 1994 murder and it represented the first time cat DNA had been used to solve a crime.

From HOWDUNNIT: FORENSICS:

FORENSIC CASE FILES: SNOWBALL THE CAT

In 1994, Shirley Duguay of Prince Edward Island disappeared. A few days later her corpse was discovered in a shallow grave along with a leather jacket, which was soaked with her blood and dotted with white cat hairs. Her estranged husband, Douglas Beamish, owned a white cat named Snowball. DNA in blood taken from Snowball matched that of the cat hairs found at the burial site, proving that those hairs came from Snowball and no other white cat. Beamish was convicted, marking this case the first time that animal DNA was used to gain a conviction.

Tinker has now followed suit in a very interesting case from Britain.

 

Howdunnit200X267

 
 

Do Identical Twins Have Different DNA?

twins-1

 

DNA profiling is considered the gold standard for individual identification. DNA-containing bodily fluids found at crime scenes can often be linked to the perpetrator with a high degree of accuracy, often measured in one per billions. It is highly individual and therefore highly accurate for identifying a given individual.

But since identical twins begin as the same fertilized egg, they have identical genetic material (DNA). After fertilization, the fertilized egg divides into two cells. To produce identical twins, these two cells separate and then each progresses forward to produce an individual. This results in two identical individuals with identical DNA. Or does it?

Twins egg:sperm

 

Standard DNA testing uses the concept of Short Tandem Repeats (STR’s). STR’s are simply short segments of DNA that repeat in certain areas of the very long DNA strand found in all of us. The number of these repeats in the various locations are what allow DNA profiling to distinguish individuals so accurately. This is a complex, though not really difficult to understand, technique which is discussed in great detail in two of my books: Forensics For Dummies and Howdunnit: Forensics.

DNA Profile

But scientists have known for years that the DNA of identical twins is not perfectly identical. It might or might not start out that way at that first cell division but for sure as the cells divide and the individual grows within the uterus, minor DNA changes can occur. These are on the level of the base pair sequences that make up the DNA chain.

Another DNA technique called Single Nucleotide Polymorphism (SNP) actually looks at each base in the DNA strand and uses this for comparison with another strand to determine if they came from the same individual. This is the direction that DNA testing is going but for now STR remains the method of choice.

Identical twins would look the same using STR analysis but a deeper analysis using SNP would reveal variations, thus allowing identification and separation of two identical twins. Let’s say, blood is left at a crime scene and that blood is matched to a particular individual. Let’s further say that this individual is an identical twin. STR DNA analysis would not distinguish between these two brothers, But if SNP is employed, the one who left the blood at the scene can be distinguished from his identical twin.

The recent French serial rape investigation involving identical twins Yohan and Elwin would be a case in point. Applying the SNP technique in this situation would likely solve the case.

Pretty cool stuff.

Howdunnit Forensics Cover

 

From HOWDUNNIT: FORENSICS:

SINGLE NUCLEOTIDE POLYMORPHISM

Single nucleotide polymorphism (SNP) is a new technique that will likely see increased use in the future. The major problem at present is that it is expensive. We saw that RFLP fragments were fairly long, a drawback that lessens their value in degraded or damaged samples (discussed later). This problem was circumvented by the discovery of STRs, which are very short fragments. But, what if the DNA examiner could use single nucleotide bases as the standard for matching? This would increase the discriminatory power of DNA even further. This is what SNP does.

Let’s say that two sequenced DNA strands looked like this:

CGATTACAGGATTA and CGATTACAAGATTA

If we searched for an “ATTA” STR repeat, these two strands would be indistinguishable

since both have two ATTA repeats. But, with single nucleotide analysis the strands differ by a single base: The ninth base in the first sequence is guanine (G), while it is adenine (A) in the second one. SNP can be used with restriction enzymes in the RFLP technique, or with PCR, where it can be easily automated. Theoretically, this will allow for discriminating two DNA samples based on a single nucleotide difference.

 

A Kiss Is Just A Kiss . . . Until It’s Evidence

red lips isolated in white

 

 

Touch DNA is the new rage in DNA testing. It’s DNA obtained from fingerprints and from objects that have been touched. This contact deposits oils, debris, and skin cells on the surface touched. Cells that contain DNA. These cells can be collected, amplified through PCR (Polymerase Chain Reaction), and profiled by STR (Short Tandem Repeat) Analysis.

But what of a kiss? Same thing. Lips pressed to a cheek will also deposit skin cells.

Ask “Pierre G,” the as yet unnamed Parisienne jewel thief who gave his victim a peck on the cheek, apparently to “allay her trauma.” Very kind of him. Unfortunately for him, the police swabbed the woman’s cheek and found usable DNA from the thief. Some acts of “kindness” go unrewarded, I guess.

 

Crime and Science Radio: Inside the Los Angeles Regional Crime Lab: An Interview with Dean Gialamas

CSR 300x250-72dpi

This Saturday, February 1, 2014 at 10 a.m. PST join Jan Burke and DP Lyle as they welcome Dean Gialamas, Director of the Los Angles County Sheriff’s Department’s Crime Lab, to the show to discuss this unique lab, what it’s like be be a crime lab director, the new federal forensic science commission, and more!

Dean Gialamas is the former director of the Orange County Crime Lab, the current director of the LASD crime lab, and was recently appointed to the first-ever National Commission on Forensic Science.  He is a past president of the American Society of Crime Lab Directors, and the president-elect of the California Association of Crime Lab Directors.

The Los Angeles County Sheriff’s Department of Scientific Services is an ASCLD/LAB-International/ISO 17025 accredited laboratory that operates from 10 facilities and employs over 300 personnel.  It serves a population of six million residents and over 100 local, state, and federal agencies.

LISTEN

LINKS:

LASD’s Scientific Services

FBI Laboratory Services

The Crime Lab Project

How Stuff Works: How Forensic Lab Techniques Work

Forensic Science Timeline

Experts Named to National Commission on Forensic Science

Announcement of Formation of the National Commission on Forensic Science

LASD Scientific Services Bureau

LAPD Scientific Investigation Division

American Academy of Forensic Sciences

American Society of Crime Lab Directors

American Society of Crime Lab Directors – Laboratory Accreditation Board

International Association for Identification

California Association of Crime Lab Directors

Hertzberg-Davis Forensic Science Center

California Association of Criminalists

Dean Gialamas at NIJ 2010 on Backlogs as a False Metric

Forensic Science Education Programs Accreditation Commission

 

The Writers Forensics Blog: 100 Top Websites to Bookmark

The crew over at FornesicScienceDegrees.org have listed The Writers Forensics Blog as one of their Top 100 Websites to Bookmark, which they describe as a “list of great sites to present practical, real-world information on the subject.” Many great sources here.

Thanks. I’m flattered.

 

 

Albert Did It

Desalvo

 

For years, controversy has surrounded the famous Boston Strangler case. Albert DeSalvo, who was killed in prison in 1973, confessed to around a dozen murders, then recanted. One of the cases at the center of the controversy was the murder of 19-year-old Mary Sullivan. Many felt Albert was responsible; others said no. The controversy can now be put to rest.

 

MSullivan1

 

The Boston Police Crime Lab tested DNA obtained from Mary’s remains and then using Familial DNA techniques compared it with a fraternal nephew of DeSalvo’s. The results suggested that a relative of the nephew’s could be the killer. That is, it could be Albert. This was enough probable cause to obtain an exhumation order to retrieve Albert’s DNA. A match was then made between his DNA and that found in the corpse of Mary Sullivan.

Albert did it.

Familial DNA also played a role in the identification of the Grim Sleeper as Lonnie Franklin

 

Organ Creation and Harvesting: Reality Imitating Art

Back in 1998, Robin Cook released CHROMOSOME 6, a medical thriller that touched on organ creation and harvesting. A very interesting concept at the time. Seems that now such fiction is approaching reality as a group of Japanese scientists are working on a system for creating “chimeric embryos” within animal wombs. The hope is that this will provide organs for human transplants. In medicine, a chimera is an organism, human or animal, that has two or more genetically distinct cell lines.

 

Chrom6

 

Reality imitating art? This will no doubt be interesting and controversial as it moves forward.

 
5 Comments

Posted by on July 18, 2013 in DNA, Medical Issues

 

DNA in a NY Minute

DNA Analyzer

 

Writers often send me questions about DNA, and most include something about the turn around time for DNA analysis. Ten years ago the answer was weeks, five years ago hours, and now it seems only minutes are required.

Engineers at the University of Washington and scientists at NanoFracture, a company in Bellevue, WA, have developed a DNA extractor that uses electrodes and not spinning centrifuges to perform the critical and time-consuming step of removing DNA from any body fluid. And it does so in only a couple of minutes. Then on to a sequencer and before you know it you have a DNA profile.

Though not commercially available yet, this technology exists and it will be interesting to see how it progresses. Of course, it’s fiction-ready right now.

 
6 Comments

Posted by on June 4, 2013 in DNA, High Tech Forensics

 

Taking a Bite Out of Crime

 

David Stoddard

 

David Stoddard and his buddies apparently thought that home invasion robberies were a slick and low risk way of making a living. After all, who would say no to three armed men?

Turns out the family’s pit bull did.

 

Pit Bull

 

As the thieves fled, the dog attacked and bit Stoddard on his leg and arm. Tragically, the dog was shot and killed. But the investigators realized that the dog had bitten one of the intruders and swabbed the deceased dog’s mouth for DNA.

Very clever.

The profile matched stellar citizen Stoddard who had been arrested for another crime–the shooting of two women, one a pregnant teenager who died. Didn’t I say he was a stellar citizen?

Of course Stoddard has pled not guilty and his defense, as voiced by his attorney John Sinn, seems to be: “My client indicates that he doesn’t have a recollection of those events.”

Really? I guess we would all forget shooting a 16-year-old mother to be and getting bitten by a pit bull. I mean, really, it could happen, don’t you think?

 
 
Follow

Get every new post delivered to your Inbox.

Join 358 other followers