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Category Archives: Medical Issues

Q and A: How Could My Character Keep Blood In a Liquid State For Later Consumption?

Q: I have a killer who drinks the blood of his victims. If he wants to bleed out a victim and wind up with blood in his freezer that he can reheat in a Mr. Coffee, I assume he’ll need some sort of anticoagulant. Is that right? Would he have to use it immediately at the murder scene? What would the average person have access to that could serve this purpose, especially if he didn’t preplan his first kill. Better still, is there some way to reconstitute the blood after it coagulates?

Craig Faustus Buck, Sherman Oaks CA

 

LEFT: Clotted and Separated Blood RIGHT: Unclotted Blood

LEFT: Clotted and Separated Blood
RIGHT: Unclotted Blood

 

A: Actually there are several ways to accomplish this. If your killer has access to the victim for several days or weeks prior to the event, he could slip some Coumadin into his food daily for two or three weeks prior to the killing. Coumadin, or warfarin, is an oral anticoagulant that works mostly in the liver to prevent blood clotting. It takes a week or so to build up to levels that would keep the blood liquid.

That might be cumbersome for your story, so there is another choice. Heparin. Heparin should be given intravenously but it works immediately as an anticoagulant. Your killer could inject a large dose of heparin right before the killing. This would of course require that he have full control of the victim or at least convince the victim that the injection was harmless. Either way, if he gave 100,000 to 200,000 units of heparin intravenously the victim’s blood would be anti-coagulated within seconds and he could then bleed him and store the blood as a liquid for an extended period of time.

Lastly, as he drained the blood he could put it into a container that contained EDTA. This is what is used in the blood vials when blood is drawn that needs to be anti-coagulated for certain tests. It’s a white powder that is available from pharmaceutical supply houses. Mixing some of this with the blood would prevent it from coagulating so it could be stored as a liquid.

As far a reconstituting it, once blood clots it immediately begins to separate into the reddish clot and the yellowish serum. Vigorous shaking or running it through a blender could remix the blood, resulting in a red liquid that he could then consume.

 
4 Comments

Posted by on July 18, 2014 in Blood Analysis, Medical Issues, Q&A

 

Visine and Munchausen Syndrome By Proxy

visine-1

 

Visine is a useful medication. I use it all the time. When the Santa Ana’s blow in SoCal and the temperature rises, the humidity falls, and eyes dry out, Visine works very well. When used properly it is very safe and effective—-but, if used improperly, it can be a deadly poison.

Actually, anything can be deadly. The difference between a drug and a poison is simply a matter of dose. What can cure, can harm; what can harm, can kill. It’s really that simple.

The active, and dangerous, ingredient in Visine is tetrahydrozoline hydrochloride. If ingested in sufficient amounts, it can cause an elevation in blood pressure, a drop in heart rate, a reduction in body temperature, nausea, vomiting, shortness of breath, blurred vision, seizures, coma, and death, to name a few effects.

The case of Samantha Elizabeth Unger underlines this danger. Seems she poisoned her two children by adding the medication to their juice. And may have done so multiple times—-which could indicate that this is a case of Munchausen Syndrome By Proxy—a psychiatric disorder in which parents harm children in order to garner attention and sympathy. Odd, but not rare.

Recently on Crime and Science Radio, Jan Burke and I interviewed Beatrice Yorker, the Dean of the College of Health and Human Services at California State University, Los Angeles and a renowned expert in Munchausen Syndrome By Proxy. Take a listen and check out some of the links for more info on the fascinating topic.

 

 

Guest Blogger: Daphne Holmes: How DNA Testing Helps Determine Paternity

DNA

 

How DNA Testing Helps Determine Paternity

The impetus for determining the paternity of a child likely dates back to the most primitive tribal cultures. Particularly in patriarchal cultures where females were regarded as the property of males, it was deemed important to ensure that a man’s “property” had not been shared, and that the virtue of the female was beyond question. As societies became more sophisticated, the need to establish paternity became as much an economic issue as a moral one. In modern cultures, paternity testing is used primarily to establish whether or not a man is responsible for providing financial support to a child, as well as determining whether the child carries any of the father’s genetic predispositions for health challenges.

Physical appearance – In more primitive cultures (some of which continue to flourish), the objectives behind determining the paternity of a child were culturally and/or emotionally based. If a child was born who lacked identifying characteristics of either parent, it was frequently assumed that the father was someone other than the woman’s mate. The repercussions to the mother were quite severe, often culminating in her death. Unfortunately – especially for the women – the comparison of obvious physical traits was highly subjective, and many women suffered dire consequences, even if their husband/mate was indeed the biological father.

Blood typing – With the early 20th century discovery that different individuals had different blood types, and the recognition in the 1920s that those blood types were genetically inherited, a more accurate means of determining paternity came into common use. It was discovered that by comparing the parents’ blood types, it was possible to determine the most likely blood type of the child. While this was admittedly a step above the “he has his father’s eyes” paternity test, it was still only about 30% accurate.

Serological testing – It was discovered in the 1930s that specific proteins not considered during blood typing could establish the presence of genetically inherited antigens that would more accurately identify the child’s biological father. Unfortunately, serological testing only improved the accuracy of paternity testing to about 40%. Hardly conclusive evidence.

Tissue typing – In the 1970s, the human leukocyte antigen (HLA) was discovered in abundance within white blood cells. When samples of this genetically inherited antigen taken from the mother and child were compared to the sample taken from the father, paternity could be established with roughly 80% accuracy. While this was a significant improvement over previous methods, the collection procedure itself was unpleasant, and the size of the sample required made it hazardous to the child, particularly if the child was less than six months old. Obviously, more work needed to be done.

DNA testing (RFLP) – In the 1980s, the technique called restriction fragment length polymorphism (RFLP) was discovered that looked at a significantly wider spectrum of variables in the blood than had been analyzed with earlier techniques. It was discovered that the offspring of two parents would have half the unique characteristics of each parent. This technique elevated the accuracy of paternity testing to the level of statistical certainty. Unfortunately, the amount of blood required for accurate sampling was, like tissue sampling, large, posing potential problems for the child. In addition, the potential for genetic mutations in the child could render a false negative, indicating that neither the woman or the man was the child’s biological parents. For these reasons, RFLP testing has been all but abandoned.

DNA Testing (PCR) – By the 1990s, the RFLP testing was replaced by the polymerase chain reaction (PCR) technique. This technique involves the computerized replication of DNA collected from even a minuscule sample that is collected anywhere on the individual’s body, then comparing the subjects’ profiles. In addition to requiring a very small sample (typically via an oral swab), the subject is not submitted to discomfort as in earlier test techniques, and the computerized analysis takes far less time, while still providing accuracy at the level of statistical certainty, 99.99%.

Author: Daphne Holmes contributed this guest post. She is a writer from www.ArrestRecords.com and you can reach her at daphneholmes9@gmail.com.

 

 

Snake Venom For Treating Seizures? On Second Thought

rattlesnake

 

In the dark ages of medicine, meaning anything before 50 to 100 years ago, those afflicted with epilepsy were treated, how shall we say, less than compassionately. They were often thought to be infected by some evil miasma, or possessed by a lurking devil or witch or warlock, or were afflicted with some contagious process. They were isolated from society, feared and shunned by all, and often subjected to horrific treatments – everything from freezing water to cutting holes in the skull to let out the evil spirits (trepanning).

 

trepan

 

This is not an uncommon reaction when people are faced with things that they don’t understand. And 100 years ago the medical profession actually understood very little.

A case in point would be Philadelphia physician Dr. Ralph Spangler who suggested that rattlesnake venom, which interestingly he had been using to treat tuberculosis (go figure), might be useful in treating epilepsy. He published an article about a Texas man who had been bitten by a rattlesnake and subsequently the epileptic seizures that had plagued him suddenly ceased. In this empirical observation of a single case he jumped to the profound conclusion that snake venom cures seizures. Thankfully cooler heads prevailed and other physicians pointed out that snake venom not only didn’t, and couldn’t, help epilepsy but rather frequently caused allergic reactions as well as hemolytic destruction of the blood. Not pretty.

The history of medicine is replete with such examples.

 

Crime and Science Radio: Deadly Doctors, Killer Nurses and other Medical Miscreants

photo 2012 cas

 

Join Jan Burke and I for a lively interview with Bea Yorker. We will delve into the very odd and not all that rare Munchausen by Proxy Syndrome as well as healthcare professionals who commit serial murders.

 

BIO: Beatrice Crofts Yorker is the Dean of the College of Health and Human Services at California State University, Los Angeles where CSULA’s forensic science program is located. She is renowned for her own research into Munchausen By Proxy, her landmark study of medical serial killers, and her publications on other topics that bring law, psychology, medicine, and ethics together.

 

LISTEN: http://www.blogtalkradio.com/suspensemagazine/2014/03/09/crime-and-science-radio-with-special-guest-bea-yorker

 

LINKS:

Medicine Net: Munchausen Syndrome: http://www.medicinenet.com/munchausen_syndrome/article.htm

Munchausen Syndrome, Cleveland Clinic: http://my.clevelandclinic.org/disorders/factitious_disorders/hic_munchausen_syndrome.aspx

Munchausen By Proxy: Cleveland Clinic: http://my.clevelandclinic.org/disorders/factitious_disorders/hic_munchausen_syndrome_by_proxy.aspx

Kid’s Health: Munchausen By Proxy Syndrome: http://kidshealth.org/parent/general/sick/munchausen.html

Medicine Net: Munchausen By Proxy: http://www.medicinenet.com/munchausen_syndrome_by_proxy/article.htm

Angels of Death: The Doctors: Crime Library: http://www.crimelibrary.com/serial_killers/weird/doctors/index_1.html

Angels of Death: The Female Nurses: Crime Library: http://www.crimelibrary.com/notorious_murders/angels/female_nurses/index.html

Angels of Death: The Male Nurses: Crime Library: http://www.crimelibrary.com/notorious_murders/angels/male_nurses/index.html

Serial Murder By Healthcare Professionals by BC Yorker, et al: http://www.ncbi.nlm.nih.gov/pubmed/17199622

Serial Murder By Healthcare Professionals by BC Yorker, et al: As PDF File: http://www.chem.sc.edu/analytical/chem107/tox/chem107_toxarticle.pdf

Psychology Today: The Medical Murder Club: http://www.psychologytoday.com/blog/the-human-equation/201206/the-medical-murder-club

 

 

Is “Real” Artificial Blood On the Horizon?

red-blood-cells

 

Blood is indeed the river of life. It carries oxygen and nutrients to all the cells of the body and removes toxic byproducts to keep everything clean and healthy. The cardiovascular system is a closed system in that it constantly recirculates, and like submarines, leaks from the system can be disastrous, and deadly. Blood is also a living, biological material and this makes it very difficult to handle. It must be taken from a living person, treated to prevent clotting, and stored in a manner that prevents decay. The logistics of this are very difficult, particularly when blood is needed in places such as war zones, very remote areas, and even in space. If someone is severely injured and in danger of exsanguinating – – the $10 word for “bleeding to death” – – then rapidly replacing this loss blood is essential. IV fluids and plasma expanders and other assorted intravenous materials can be given to buy time, to keep the volume in the system to an adequate level, and to keep everything circulating, but these materials have a major drawback – – they don’t carry oxygen. So the only life-saving remedy is to replace the blood.

Over the years there have been many attempts to develop artificial blood, a product that would carry oxygen and be logistically more friendly. Something that did not require anticoagulation, refrigeration, and care in its transport and storage. Something that could be carried and stored like a bottle of water. Many of these endeavors have proven to be unsuccessful.

Blood substitutes have traditionally been based on hemoglobin, the oxygen-carrying molecule within the red blood cells (RBCs). Products such as HemoPure (made from bovine hemoglobin), PolyHeme (made from outdated human blood), and HemAssist (based on cross-linked hemoglobin) all seemed promising but safety issues arose with each and these have not been completely resolved.

Other forms of “artificial blood” have been based on perfluorocarbon emulsions. These too have faced many problems.

Another problem with blood therapy is keeping a steady and safe supply. There are only so many donors and the blood’s shelf-life is not all that long. If blood could be manufactured so that an adequate and steady supply could be maintained, this would be a giant step forward.

Well, now it seems that manufactured truly artificial blood might be on the horizon. A group at the University of Edinburgh is beginning clinical trials on a process for making red blood cells from stem cells. Since these would be “real” RBCs, the technique holds promise.

 
2 Comments

Posted by on April 30, 2014 in Medical History, Medical Issues

 

Futuristic Robotic Surgery Is Here

Robotic Device

 

My second Dub Walker thriller HOT LIGHTS, COLD STEEL dealt with the future of robotic surgery. Future as in way down the road. But now it seems it’s not all that far away. Virtual Incision in Lincoln, Nebraska is working on a very clever device that could make space missions safer. Very cool stuff.

 

HLCSCover300X450

 

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/

 
 

Crime and Science Radio: Sex, Lies, and Crime: An Interview With Sex Crimes Expert and Best-Selling Author Linda Fairstein

CSR 300x250-72dpi

 

Join Jan Burke and I as we discuss sex crimes with best-selling author Linda Fairstein.

Linda Fairstein is an honors graduate of Vassar College and the University of Virginia School of Law, a former prosecutor, and one of America’s foremost legal experts on crimes of violence against women and children. For three decades, she served in the office of the New York County District Attorney, where she was Chief of the Sex Crimes Prosecution Unit for twenty-five years. She was the lead attorney in the famous the Robert Chambers “Preppy Murder” case. She is an internationally bestselling author of a series of crime novels, which feature Manhattan prosecutor Alexandra Cooper. Linda is also the author of a non-fiction work. Sexual Violence: Our War Against Rape, which was a New York Times Notable Book of the Year. She is a sought-after media consultant on the issue of the criminal justice system and crimes of violence against women for major networks such as CNN, MSNBC, and cable affiliates. She continues to practice law as a pro bono representative of victims of violence. She and her husband Justin Feldman live in Manhattan and on Martha’s Vineyard.

linda-fairstein

 

LISTEN: http://www.blogtalkradio.com/suspensemagazine/2014/02/21/crime-and-science-radio-with-linda-fairstein

LINKS:

Linda Fairstein Website: http://www.lindafairstein.com

Linda Fairstein Facebook Page: https://www.facebook.com/LindaFairstein

Linda on Twitter: @lindafairstein

Alex Cooper Series on Goodreads: https://www.goodreads.com/series/43692-alexandra-cooper

USA Today Interview (2013): http://www.usatoday.com/story/life/books/2013/08/16/linda-fairstein-central-park-sex-crimes/2656599/

Sex-assault Case Puts Focus on Police Unit, Not Quite as Seen on TV: http://www.nytimes.com/2011/05/19/nyregion/strauss-kahn-case-puts-focus-on-real-special-victims-squad.html?pagewanted=all&_r=0

Inside the NYPD’s Special Victims Division: http://www.newsweek.com/inside-nypds-special-victims-division-67761

New York’s DA’s Office Trial Division: http://manhattanda.org/trial-division

Crime Library: A Killing in Central Park: The Preppy Murder Case: http://www.crimelibrary.com/notorious_murders/not_guilty/park/4.html

Jennifer Levin’s Mother Remembers “Preppy Murder” Case: http://newyork.cbslocal.com/2011/09/02/jennifer-levins-mother-remembers-preppy-murder-case/

Murderpedia: Robert Chambers: http://murderpedia.org/male.C/c/chambers-robert.htm

Children Of The Night: http://childrenofthenight.org

Sex Slaves: The Psychology of Mastery: http://www.crimelibrary.com/criminal_mind/sexual_assault/sex_slaves/1_index.html

Joyful Heart Foundation

RAINN: Rape, Abuse and Incest National Network

Cleveland Plain Dealer Series on Ohio’s sexual assault kit backlog investigations

Houston Chronicle article re Houston elimination sexual assault kit backlog

The Guardian’s story on Detroit Prosecutor Kym Worthy’s fight to investigate 11,000 abandoned sexual assault kits

Contra Costa Times: “California bill calls for evidence in unsolved, neglected rape cases to get attention”

Inside the Lives of American Sex Slaves: National Geographic

Coalition to Abolish Slavery and Trafficking

 

LindaFairstein_TerminalCity_CV.indd

 

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.

 
 
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