WRONGFUL CONVICTIONS CLASS  

DNA: A Primer for UMKC Wrongful Convictions Class

[In preparing these materials, Prof. Moenssens makes it clear that he is neither a biochemist nor a population geneticist, though he has been close to the development of the forensic uses of DNA. As special counsel to Lifecodes, Inc., one of the two companies that pioneered forensic DNA in the U.S., he authored an amicus brief in 1987 in the very first appellate case to decide the admissibility of DNA in this country, namely State v. Andrews, 533 So.2d 841 (Fla. App. 5 Dist. 1988). In its decision approving of the admission of DNA evidence, the Florida court quoted extensively from the 3^rd edition of Prof. Moenssens’ "Scientific Evidence in Criminal Cases" book. A 93-page chapter, authored by Kenneth E. Melson, is included as Chapter 15 in the 4^th edition of "Scientific Evidence in Civil and Criminal Cases," 1995, Foundation Press - by Moenssens, Starrs, Henderson & Inbau.]

1. What is DNA? The initials "DNA" stand for deoxyribonucleic acid, the building blocks of life, which are contained in a ribbon-like molecule in the nucleus of almost all human cells. This DNA molecule, first described as being in the form of a double helix by scientists Crick and Watson in 1953 (they both received Nobel prizes for their work), contains the design for every living organism. Research in molecular biology and genetics (which actually had its start when, in 1865, the Austrian Monk Gregor Mendel, crossed peas to prove that traits such as color and shape were controlled by hereditary factors) did not become applied to forensic uses, in criminal cases where biological evidence was available and in civil cases seeking to establish paternity, until 1985 in Great Britain, and almost immediately thereafter in the United States.

The first conviction obtained by DNA evidence occurred in England in 1987. In the United States, the technology transfer from the pioneering research laboratories (Lifecodes, and Cellmark Diagnostics) to the FBI Laboratory and other crime laboratories did not occur until the early to mid-1990's. The first appellate decision in the U.S. on the admissibility of DNA-based expert opinion evidence occurred in 1988. Since the novel technique drew heavily on existing research in the medical field, its adoption as a means of "identifying" individuals was rapid.

2. Some basic "cell" stuff and what is the significance of DNA in human beings?  Human beings have approximately 80 to 100 trillion cells in their bodies. Most cells exist in loosely organized groups in which they have special jobs to do. There are, for instance, nerve cells carrying information from the eyes to the brain, nerve cells sending instructions from the brain to our limbs, tissue cells with different functions, etc. All of these cells are also alive in the sense that they breathe, take in food, get rid of water, grow up, reproduce, and finally die.

Within each cell are chromosomes, which are structures of DNA and proteins that carry the genetic material making up an individual. Every human nucleated cell has 22 matched pairs of non-sex chromosomes and two sex chromosomes. Along the rod-like chromosomes in a cell’s nucleus are genes, which are the basic carriers of inherited traits. A human being possesses nearly 100,000 genes. Each gene contains a coded sequence of DNA nucleotides (the combination of a base with a sugar and phosphate group). Various combinations of these coded sequences of the DNA strand are called "alleles."

Since the human body contains so many trillions of cells, they are obviously extremely small. There would probably be in excess of one million cells in an area of human skin no larger than a square inch. We cannot see, with the naked eye, what a "cell" looks like, and yet within each cell are located these even smaller things. Just try to visualize:

(1) Each of the 46 chromosomes in just one cell has a DNA molecule in the form of a double helix. If we were to stretch out the molecule of just one of these cells, it would be six to nine feet in length.

(2) If we were to stretch out like an uncoiled rope, end-to-end, all of the DNA molecules contained in the 100 trillion cells in just one human body, the rope would be 93 billion miles long!

3. What is the "double helix" thing that one sees on the opening page of your website? The double helix in the nuclear DNA molecule may be compared to a coiled rope ladder, with two side supports composed of sugar and phosphate groups that are connected with steps or rungs. Each "step" contains a combination of two substances called "bases." There are only four different bases; they are called: adenine (A), cytosine (C), guanine (G), and thymine (T). Each one of these "steps" is a nucleotide. These nucleotides repeat themselves in their arrangement of base pairs as they form a strand of the double helix, but the bases that make up a nucleotide are always paired in the same manner. A always bonds with T. G always bonds with C. While these bases always link to each other in the same manner – that is, A-T, T-A, G-C, or C-G – they do so in sequence lengths of immense variability. If you take, for example, a strand of DNA that contains only 10 nucleotides (base pairs), the number of possible variations is four-to-the-tenth-power or 1,048,580 different possible sequences. The order, or the sequence, of these base pairs is the genetic code of an individual. Specific locations along the DNA molecule may contain anywhere from a few base pairs to thousands of base pairs.

4. Is it hard to do DNA "analysis" to establish identity?  The analysis of DNA is complex and there are a number of different ways in which one may proceed. The most "specific" method for establishing a "match" is called the Restriction Fragment Length Polymorphism method, or RFLP in short. This technique is based on the knowledge that while most DNA is the same for all individuals, there are nevertheless small portions of the DNA strand that contain sequences of base pairs that have been found to be extremely variable or "polymorphic." By locating these specific sequences in two different samples of biological material – one of unknown origin (usually the "crime scene" sample), the other of a known person – it can be determined whether they "match." This is a process which calls for a number of different steps, involving the extraction of DNA, the isolation of the extremely polymorphic sequences that will be targeted so that the rest of the DNA can be discarded, and the comparison of what is left from the two (or more) samples.

When a "match" is found – that is, the same Variable Number of Tandem Repeats (VNTRs in short) – are believed to exist in both samples, the molecular biologist has finished his work.

This does not tell us, however, what the meaning of our finding is, since we don’t know, at this stage, how frequently these polymorphic sequences may be found to exist in a given population sample. For that determination, forensic DNA analysts turn to two entirely different disciplines: population genetics, and statistics.

Using the blood banks as a reservoir for analysis, population geneticists have been able to calculate how often, in a given population sample, a particular highly variable base pair sequence occurs. Let’s take a simplified hypothetical example where we look at just three locations on the DNA strand. Say that in targeting the various polymorphic regions of the DNA strand, the microbiologists find that at Site A the same variation occurs once in the DNA of every 80 humans. The Site B characteristic sequence on the DNA molecule might be found to be occurring only once in every 400 individuals. By contrast, the Site C characteristics have been determined to occur once in every 100 individuals. Proceeding from the assumption that the way each site’s sequence occurs is independent of all the other sites, we can now calculate, by applying Newcomb’s theory of probabilities, how likely it is that among the population at large the exact same three sequences found at sites A, B and C will occur. This is done by multiplying the probabilities: 80 x 400 x 100 which gives us 320,000. Thus, the probability that identical sequences will occur at all three locations on the DNA of two different individuals (in a random population sample) is one in 320,000.

Today, most DNA analyses target at least ten different sites, or loci (locations), on the DNA strand. The FBI currently uses probes for 13 different loci. It can be readily seen that this process of multiplying the probabilities at ten or more sites easily reaches into the one-in-several-billion that we are used to hearing when DNA results are discussed in the media.

5. Is it correct to call DNA "the ultimate identifier"? A book written for the general public which attempts to explain DNA technology starts by calling DNA the ultimate identifier. Can DNA positively identify a particular individual? The answer is both "yes" and "no," depending on your perspective. Every individual’s DNA is probably different from the DNA of every other individual, but until we have the ability to examine each and every sequence of a complete DNA strand – something that will probably never occur – we must be satisfied with a calculation based on what we know about a relatively small number of portions to the DNA, to which we then apply the law of probabilities (and all kinds of other scientific principles that are not relevant for our discussion).

These "random population sample" calculations do not necessarily hold true within a family. The same sequences that are very variable among the population at large are not as variable among people who are genetically related. In fact, identical twins have, as far as we currently know, the same DNA. We will probably develop, at some later time, the technology to distinguish even between identical twins based on the extremely subtle "errors" that are introduced in an individual’s DNA when the cells replicate themselves..

The important point to remember is that it is possible to find a number of variable locations between two unrelated individuals that match exactly. See the story on Prof. Moenssens’ website titled "A Mistaken DNA Identification? – What Does It Mean?", which can be accessed at http://www.forensic-evidence.com/site/EVID/EL_DNAerror.html. The site discusses the case of a person charged with a crime he had not committed after his DNA was found to "match" the DNA sample already contained in Great Britain’s database of 470,000 people. Because the potential error rate with which the "identification" was made concluded that the suspect’s DNA matched that of the crime scene sample in seven loci, the probability of the same sequences occurring in two different individuals was one in 37 million. He was promptly charged with the commission of the crime, solely on the basis of this "match." When later retesting was done at the request of the defense, it was established that while the first seven loci tested were found to match, when additional loci were also tested, differences began to appear which showed the suspect was not the contributor of the crime scene DNA.

As our DNA databases become larger, such duplications – while still extremely rare – are nevertheless likely to occur with ever greater frequency, unless we also expand the number of loci that are targeted for analysis.

6. Are there DNA comparison methods that are different from RFLP? Yes. In addition to RFLP – a method that is time consuming since it involves subjecting one DNA sample to repeated analyses for as many locations (loci) as are sought to be tested – there are other methods that are much faster but also less specific. One such method is the Polymerase Chain Reaction (PCR) method, which selectively duplicates (or amplifies) very short segments of DNA. It is a method that can be used when very little DNA is present. [RFLP requires typically that at least 10 to 50 ng (nanograms) of high molecular weight DNA be present. PCR requires much less, theoretically down to a as little as a single nucleated cell.] For that reason, PCR is used often to analyze the DNA that may be found in the root of hairs, or in the saliva retrieved from cigarette butts or licked postage stamps.

The method of analysis by PCR is much simpler and faster, with the analysis being completed and obtainable in days, as opposed to weeks required for RFLP.

7. What is Mitochondrial DNA or mtDNA? The DNA analysis which has been discussed in the preceding sections of this Primer is based on an analysis of DNA contained in the nucleus of the cell, which is why it is called "nuclear DNA." Heredity insures that the nuclear DNA comes from a combination of paternal and material characteristics.

In the mitochondria of the cell (located outside the nucleus), there is also DNA-like information to be found, but that information is inherited only through the maternal line, and therefore does not contain as great a genetic variation as can be found in nuclear DNA. In fact, all maternally related persons share the same mtDNA sequences. MtDNA analysis is also more expensive and takes longer to do than either PCR or RFLP. While not a unique method of personal identification, mtDNA is very useful in excluding suspects.

In forensic analysis, this is particularly useful in the examination of hairs. Hair that falls out naturally, or is cut off, does not contain nuclear DNA. (The root of a hair, if attached to a hair sample, contains such cells and can therefore be analyzed by PCR or even RFLP.) An ordinary hair shaft without a root does contain, however, mitochondrial DNA that was transmitted to an individual through the maternal line. This hereditary link may assist in either establishing a possibility that the mtDNA came from the defendant, or it may establish positively that the mtDNA could not have come from the defendant – an exclusion

Mitochondrial DNA is also more stable than nuclear DNA so that it is sometimes available in samples that are too degraded to allow the recovery of nuclear DNA that is suitable for testing.

8. What is the significance of DNA in establishing innocence? This topic is explored in the assigned text: Barry Scheck, Peter Neufeld, Jim Dwyer, ACTUAL INNOCENCE, March 2001 (Signet Printing).

While probability calculations made after a "match" has been determined to exist still permit, at least theoretically, erroneous "identifications," when the DNA of a suspect/defendant/inmate is found to be different from that extracted from a biological sample obtained at a crime scene, then the exclusion is definitive – that is, the crime scene DNA could not have come from the suspect/defendant/inmate under any circumstance.

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1. In the April, 2001, issue of the American Bar Association Journal, see the article by Mark Hansen, "The Great Detective," at p. 37. The article’s subheading states, "DNA evidence, the best police investigative tool since the advent of fingerprinting, also helps free the innocent. As exonerations mount, more are questioning their faith in the criminal justice system."

2. Read the file titled titled "DNA Statistics Found Insufficient to Convict without Corroboration" at http://www.forensic-evidence.com/site/EVID/DNA_Watters.html. The file contains the opinion of the (British) Court of Criminal Appeals in the case of R. v. Watters, decided October 19, 2000.

3. An Interview With DNA Forensics Authority Dr. Bruce Weir can be found at

4. "Phenotype v. Genotype: Why Identical Twins Have Different Fingerprints," by Edward P. Richards, at

http://www.forensic-evidence.com/site/ID/ID_Twins.html

5. "Instructing Jury That DNA Testing Is ‘Reliable Scientific Technique’ Held Improper

by Appeals Court," at http://www.forensic-evidence.com/site/EVID/EL_dna_instr_bad.html

Missouri has recently adopted a statute allowing access to DNA evidence for post-conviction testing.  The Missouri Supreme Court had previously adopted a Court Rule providing access but vacated the Rule when the General Assembly adopted the statute.  See Mo. S. Ct. R. 29.17,  Post-Conviction Motion for Forensic DNA Testing not Available at Trial (adopted 2/20/01, vacated 8/21/01).

547.035. 1. A person in the custody of the department of corrections claiming that forensic DNA testing will demonstrate the person's innocence of the crime for which the person is in custody may file a post-conviction motion in the sentencing court seeking such testing. The procedure to be followed for such motions is governed by the rules of civil procedure insofar as applicable.

2. The motion must allege facts under oath demonstrating that:

(1) There is evidence upon which DNA testing can be conducted; and

(2) The evidence was secured in relation to the crime; and

(3) The evidence was not previously tested by the movant because:

(a) The technology for the testing was not reasonably available to the movant at the time of the trial;

(b) Neither the movant nor his or her trial counsel was aware of the existence of the evidence at the time of trial; or

(c) The evidence was otherwise unavailable to both the movant and movant's trial counsel at the time of trial; and

(4) Identity was an issue in the trial; and

(5) A reasonable probability exists that the movant would not have been convicted if exculpatory results had been obtained through the requested DNA testing

3. Movant shall file the motion and two copies thereof with the clerk of the sentencing court. The clerk shall file the motion in the original criminal case and shall immediately deliver a copy of the motion to the prosecutor.

4. The court shall issue to the prosecutor an order to show cause why the motion should not be granted unless:

(1) It appears from the motion that the movant is not entitled to relief; or

(2) The court finds that the files and records of the case conclusively show that the movant is not entitled to relief.

5. Upon the issuance of the order to show cause, the clerk shall notify the court reporter to prepare and file the transcript of the trial or the movant's guilty plea and sentencing hearing if the transcript has not been prepared or filed.

6. If the court finds that the motion and the files and records of the case conclusively show that the movant is not entitled to relief, a hearing shall not be held. If a hearing is ordered, counsel shall be appointed to represent the movant if the movant is indigent. The hearing shall be on the record. Movant need not be present at the hearing. The court may order that testimony of the movant shall be received by deposition. The movant shall have the burden of proving the allegations of the motion by a preponderance of the evidence.

7. The court shall order appropriate testing if the court finds:

(1) A reasonable probability exists that the movant would not have been convicted if exculpatory results had been obtained through the requested DNA testing; and

(2) That movant is entitled to relief.

Such testing shall be conducted by a facility mutually agreed upon by the movant and by the state and approved by the court. If the parties are unable to agree, the court shall designate the testing facility. The court shall impose reasonable conditions on the testing to protect the state's interests in the integrity of the evidence and the testing process.

8. The court shall issue findings of fact and conclusions of law whether or not a hearing is held.

547.037. 1. If testing ordered pursuant to section 547.035 demonstrates a person's innocence of the crime for which the person is in custody, a motion for release may be filed in the sentencing court.

2. The court shall issue to the prosecutor an order to show cause why the motion should not be granted. The prosecutor shall file a response consenting to or opposing the motion.

3. If the prosecutor consents to the motion and if the court finds that such testing demonstrates the movant's innocence of the crime for which he or she is in custody, the court shall order the movant's release from the sentence for the crime for which testing occurred.

4. If the prosecutor files a response opposing the movant's release, the court shall conduct a hearing. If a hearing is ordered, the public defender shall be appointed to represent the movant if the movant is indigent. The hearing shall be on the record. The movant shall have the burden of proving the allegations of the motion by a preponderance of the evidence.

5. If the court finds that the testing ordered pursuant to section 547.035, demonstrates the movant's innocence of the crime for which he or she is in custody, the court shall order the movant's release from the sentence for the crime for which the testing occurred. Otherwise, relief shall be denied the movant.

6. The court shall issue findings of fact and conclusions of law whether or not a hearing is held. An appeal may be taken from the court's findings and conclusions as in other civil cases.