Tag Archive for: electropherogram

Law enforcement officers collect a variety of evidence at crime scenes, such as bullet fragments, weapons, narcotics, and fingerprints. In addition, police gather body fluids, skin cells, bones, and hairs, hoping that one or more of those substances will contain a suspect’s DNA.

But where, you might ask, is the DNA located? Well, it’s certainly not doing the backstroke in the pool of blood that leaked from a fallen victim of a gunshot. Instead, the DNA evidence sought by police—nuclear DNA—is contained within the nuclei of cells.

Cells, the Home of Nuclear DNA

All cells in our body are made up of a cell wall (cell membrane), cell fluid (cytoplasm) and a nucleus, with the exception of red blood cells and platelets. Since neither of latter two have a nucleus they do not contain DNA.

Nuclear DNA is made up of genetic material from our fathers and mothers. The nucleus of each cell contains a pair of chromosomes—, one from each parent.

Each cell typically contains 23 pairs of chromosomes, for a total of 46. Twenty-two of the pairs are called autosomes, and they look identical in both male and female humans. The 23rd pair are the sex chromosomes and they are distinctly different between males and females. Females have two copies of the X chromosome. Males have one X and one Y chromosome.

As evidence in criminal matters, DNA serves a dual purpose—identifying an individual as the source of the DNA found on an evidence item, or to exclude the individual as the contributor of the collected DNA evidence.

Now, we’ve briefly and generally discussed that DNA lives in cells, and those cells are where scientist go to retrieve the DNA needed for testing. And we know that DNA is readily found in body fluids, skin cells, bones, and for many years it was believed that testing hair for DNA was only possible if the bulb/root at the base of the hair shaft was intact. This was so because the keratinization process that creates the hair shaft during its growth often breaks down (lyses ) cell membranes.

DNA IS present, though, in hair shafts, but in small quantities. It’s quite short and fragmented, which is similar to DNA found in ancient remains. So yes, like testing DNA found remains of wooly mammoths and other beings and bits and bobs from long ago, it is possible to isolate nuclear DNA from rootless human hair samples.

In fact, to make this possible, a company called InnoGenomics uses a magnetic bead extraction system that’s specifically optimized for the process of capturing low-level, highly degraded DNA.

By combining InnoGenomics’ two DNA typing kits together—InnoXtract and InnoTyper 21 (IT21), the isolation and typing of nuclear DNA from rootless hair shafts is quite achievable. And, the process is compatible with Capillary Electrophoresis (CE) instruments, such as Promega’s Spectrum CE System.

So yes, crime writers, the heroes of your tales have a tool to add to their crimefighting toolboxes, because it is indeed possible to obtain nuclear DNA from hair shafts.

DNA Testing in General

The first step in the testing process is to extract DNA from the evidence sample. To do so, the scientist adds chemicals to the sample, a process that ruptures cells. When the cells open up DNA is released and is ready for examination.

Did you know it’s possible to see DNA with the naked eye? Well, you can, and at the bottom of this page you’ll learn how see the DNA that you, in your home kitchen, can extract DNA from split peas.

After DNA is extracted it’s then loaded into wells inside the genetic analyzer.

Scientist placing a well plate containing 96 individual wells into a genetic analyzer. Below right in photo is a closeup of a well plate.

Electric current separates the DNA, sending it from the wells through narrow straw-like tubes called capillaries. During its journey through the analyzer, DNA passes by a laser. The laser causes the DNA loci (a gene’s position on a chromosome) to fluoresce as they pass by, which allows a tiny camera to capture their images.

The image below shows DNA’s path from the wells through the capillaries past the laser.


At the end of the testing, the equipment produces a graph/chart called an electropherogram, a chart/graph of peaks and valleys that precisely pinpoints where genes are located.

An allele is a term that describes a specific copy of a gene. Each allele occupies a specific region on the chromosome called a gene locus. A locus (loci, plural) is the location of a gene on a chromosome.

Peaks on the graph depict the amount of DNA strands at each location (loci). It is this unique pattern of peaks and valleys that scientists use to match or exclude suspects.


The image below, as ominous as it appears, is an electropheragram showing the DNA of a strawberry.


Serial Killer Challenges DNA Results

*The following text regarding the appeal from serial killer Timothy W. Spencer, The Southside Strangler,” is from the US Court of Appeals for the Fourth Circuit. Spencer’s case was the first in the U.S. based on DNA evidence that resulted in the death penalty. I served as a witness to Spencer’s execution. Click here to read about my experience.

“Timothy W. Spencer, Petitioner-appellant, v. Edward W. Murray, Director, Respondent-appellee, 5 F.3d 758 (4th Cir. 1993)

US Court of Appeals for the Fourth Circuit – 5 F.3d 758 (4th Cir. 1993)Argued Oct. 28, 1992. Decided Sept. 16, 1993

J. Lloyd Snook, III, Snook & Haughey, Charlottesville, VA, argued (William T. Linka, Boatwright & Linka, Richmond, VA, on brief), for petitioner-appellant.

Donald Richard Curry, Sr. Asst. Atty. Gen., Richmond, VA (Mary Sue Terry, Atty. Gen. of Virginia, on brief), for respondent-appellee.

Before WIDENER, PHILLIPS, and WILLIAMS, Circuit Judges.


WIDENER, Circuit Judge:

Timothy Wilson Spencer attacks a Virginia state court judgment sentencing him to death for the murder of Debbie Dudley Davis. We affirm.

The gruesome details of the murder of Debbie Davis can be found in the Supreme Court of Virginia’s opinion on direct review, Spencer v. Commonwealth, 238 Va. 295, 384 S.E.2d 785 (1989), cert. denied, 493 U.S. 1093, 110 S. Ct. 1171, 107 L. Ed. 2d 1073 (1990). For our purposes, a brief recitation will suffice. Miss Davis was murdered sometime between 9:00 p.m. on September 18, 1987 and 9:30 a.m. on September 19, 1987.

Miss Davis was murdered sometime between 9:00 p.m. on September 18, 1987 and 9:30 a.m. on September 19, 1987. The victim’s body was found on her bed by officers of the Richmond Bureau of Police. She had been strangled by the use of a sock and vacuum cleaner hose, which had been assembled into what the Virginia Court called a ligature and ratchet-type device. The medical examiner determined that the ligature had been twisted two or three times, and the cause of death was ligature strangulation. The pressure exerted was so great that, in addition to cutting into Miss Davis’s neck muscles, larynx, and voice box, it had caused blood congestion in her head and a hemorrhage in one of her eyes. In addition her nose and mouth were bruised. Miss Davis’s hands were bound by the use of shoestrings, which were attached to the ligature device. 384 S.E.2d at 789.

Semen stains were found on the victim’s bedclothes. The presence of spermatozoa also was found when rectal and vaginal swabs of the victim were taken. In addition, when the victim’s pubic hair was combed, two hairs were recovered that did not belong to the victim. 384 S.E.2d at 789. The two hairs later were determined through forensic analysis to be “consistent with” Spencer’s underarm hair. 384 S.E.2d at 789. Further forensic analysis was completed on the semen stains on the victim’s bedclothes. The analysis revealed that the stains had been deposited by a secretor whose blood characteristics matched a group comprised of approximately thirteen percent of the population. Spencer’s blood and saliva samples revealed that he is a member of that group. 384 S.E.2d at 789.

Next, a sample of Spencer’s blood and the semen collected from the bedclothes were subjected to DNA analysis. The results of the DNA analysis, performed by Lifecodes Corporation, a private laboratory, established that the DNA molecules extracted from Spencer’s blood matched the DNA molecules extracted from the semen stains. Spencer is a black male, and the evidence adduced at trial showed that the statistical likelihood of finding duplication of Spencer’s particular DNA pattern in the population of members of the black race who live in North America is one in 705,000,000 (seven hundred five million). In addition, the evidence also showed that the number of black males living in North America was approximately 10,000,000 (ten million). 384 S.E.2d at 790.”

How You Can Easily Extract DNA From Split Peas!

Easy “pea-sy” DNA extraction

In the days before DNA testing became available for use in criminal cases, cops, prosecutors, judges, and juries relied on other physical evidence to send bad guys to jail—fingerprints and footprints, soil, glass fragments, trace evidence, etc. Those things along with confessions and eyewitness testimony were the building blocks used to convict the guilty.

Then, when DNA arrived on the scene, well, it soon became apparent that somehow officials had made a few boo-boos along the way and had sent more than a handful of innocent men and women to jail for crimes they didn’t commit. DNA testing of old evidence, in fact, exonerated people like our friend Ray Krone who served ten years in prison, three of which were on death row, for a murder he didn’t and couldn’t have committed.

Ray as an inmate at Arizona State Prison in Yuma

Ray Krone could’ve easily been eliminated as a suspect had DNA testing been conducted at the time of the investigation. Instead, his conviction was based on bite mark evidence, a test/examination/comparison method that’s been found to be unreliable.

DNA test results were used in court cases as early as the mid 1980s. Ray was convicted in the early 90s, without the benefit of DNA testing, a simple test that would have prevented him from serving time in prison as an honest, clean-handed man.

Nowadays, to weed out the innocent, DNA testing is routinely performed in the early stages of criminal investigations. And it helps … some. The use of DNA tests in post-conviction cases and appeals sometimes leads to exonerations, such as, for example, Ray Krone’s release from prison.

Electropherogram – a chart produced by testing equipment after DNA sequencing is completed.

Unfortunately, and what most members of juries do not understand, is that during a typical criminal investigation, in only about 10-20 percent of all cases do cops find testable biological evidence. In spite of this low percentage, some juries still expect a case to hinge on DNA results. However, without something to test, of course, there’ll be no electropherograms pointing to a specific suspect.

Sometimes, even with the presence of DNA, those results are not always definitive.

Electropheragram showing tested DNA of two subjects, and a mixture of DNA collected from a victim. Results showing a mixture make it difficult to point to any one suspect.

But let’s go back to the 10-20 percent figure, the number of cases where testable biological evidence is located and collected by investigators and then subsequently tested by laboratory scientists and other experts.

At the upper end, the 20 percent range, that leaves 80 percent of all criminal cases that are solved by using other means of crime-solving, such as the aforementioned fingerprints and footprints, soil, glass fragments, trace evidence and, of course, detectives going about the business of good old-fashioned door-knocking and talking to people. The combination of the physical evidence and confessions and eyewitness testimony is what leads to the majority of criminal convictions.

Sadly and dismally disastrous, without mostly foolproof scientifically tested evidence, courts must rely on human testimony, humans whose memories often fluctuate. Police investigators who enter a crime scene with a serious and dreaded case of tunnel vision. Prosecutors who do the same once the already skewed/tunnel-vision-tainted, unreliable witness’ flawed statement evidence is presented to them,

Overworked and underpaid public defenders aren’t always up to date on current scientific practices and the laws governing them. Those same attorneys carry heavy caseloads which stretches their time to a breaking point so thin that they can’t possibly devote the amount of time needed to decently defend their appointed clients. Their budgets are minimal, meaning expensive testing and other necessities for their clients’ defenses are practically nonexistent.

Post-conviction procedures (motion for new trials, ineffective assistance of council, appeals to address the lack of scientific testing to prove innocence) are a huge uphill climb for people who’ve been incarcerated. This is especially so for the poor.

Those of meager means often have no alternative other than to wade through prison law libraries, hoping to make sense of the legal jargon that fits their situation. They sometimes employ a jailhouse lawyer to help, paying for his services by whatever means available—cleaning his cell, cooking meals, shining shoes, and even purchasing items for them from the commissary, or having family members on the outside send money to the amateur legal eagle.

The wealthy, of course, have outside resources to help with the filing of necessary paperwork. But there’s sometimes a bad egg in this bunch, such as the high-priced, fancy-smancy defense attorney I overheard telling his client who’d just received 37 months in federal prison for possessing crack cocaine worth little more than $100, that for an additional $25,000 he could arrange to have him serve less time on home confinement. That’s fair, right?

And, there’s the Innocence Project who helps the wrongly convicted.

Aside from the obvious, there’s a real problem with the aftermath that’s sure to arise after retroactively clearing prisoners of their crimes based on DNA evidence.

Yes, when all the dust settles after all the men and women who’ve been wrongfully convicted and then cleared by the use of DNA evidence are out of prison with their recoreds expunged and their names cleared, there will still be hundreds if not thousands of people still behind bars because their convictions were based on the bad memory of a witness, a cop or prosecutor with tunnel vision, being in the wrong place at the wrong time, a mistake made at the lab during evidence analysis (mislabel an item, etc., tainted evidence, such as the accidental transfer of a fingerprint or even DNA evidence).

Someday soon there will be a false sense that DNA has cleared ALL the innocent people, leaving  those behind who  surely must be guilty of their crimes because there was no scientific evidence to prove otherwise. But we know this can’t be so. Why not? Because of human error.

Yes, it is indeed possible to transfer a fingerprint, even accidentally.

Tertiary DNA Transfer

It’s possible that DNA can be accidentally transferred from one object to another. A good example could be the killer who shares an apartment with an unsuspecting friend. He returns home after murdering someone and then tosses his blood-spatter-covered shirt into the washer along with his roommate’s clothing. The machine churns and spins through its wash cycles, an action that spreads the victim’s DNA throughout the load. Police later serve a search warrant on the home, seize the clothing, and discover the victim’s DNA on the roommate’s jeans. The innocent roommate is arrested for murder.

The list of human error possibilities is extremely long and, unfortunately, there’s no magic DNA bullet to help clear the innocent folks convicted based on an accident. Their battles are practically hopeless. Laws and courts make it nearly impossible for people already serving time to have a judge revisit their cases.

Odds are, that hopelessness follows a few of the condemned all the way to the execution chamber, where it is indeed conceivable that an innocent man could be, and most likely has been, put to death.

And, well, I suppose it’s possible that given the right/wrong circumstances, anyone, even you, could find themselves behind bars for a crime they didn’t commit.