As we honor Mothers this month and Fathers next month, I thought it would be fun to do a two part series on DNA… since these are the building blocks of how we are fearfully and wonderfully created!
In the beginning…. two distinct sets of gene pools merge and in those genes are all the DNA we will ever need to become who we are today. The term DNA gets thrown around a lot, so let’s break down the concept of DNA and look at a couple different types and how they are used in crime solving.
DNA stands for deoxyribonucleic acid. It is found in the cells of all living things (plants and animals included). A complete set of DNA is unique to each individual and only identical twins share the same DNA.
DNA contains a set of gene codes arranged along 25,000 chromosomes that contains all the information about a person’s genetic make-up and well-being from birth to death. Your hair and eye color and what diseases you’re prone to are found in DNA.
DNA was first discovered in 1868, but it wasn’t until the 1950s that scientists figured out how DNA looked like. And only in the late 1980s that DNA started to be used forensically to link suspects and victims to crimes.
How doe DNA works? We’ll start with the building blocks of DNA science and then see how it applies to forensic science.
Nucleotide
What is it?
The core DNA unit consists of a base attached to a sugar-phosphate strand. The four bases contain nitrogen and they are: Adenine, Cytosine, Guanine, and Thymine. Adenine always pairs with Thymine. And Guanine always pairs with Cytosin. This core unit of DNA repeats itself over and over and over in one lone double helix configuration.
Mitochondrial DNA (mtDNA)
What is it?
Mitochondrial DNA is inherited from the mother only and is found outside the cell. It provides the cell with energy and there is lots of it. Hundreds or even thousands of mitochondria live on a single cell; compared with just one set of nuclear DNA in each cell. MtDNA is extracted from hair shafts, teeth, bone, organs and tissues.
How is it used to solve crimes?
Mitochondrial DNA is used in cases of trying to prove identity from nuclear DNA when the body has been destroyed or disintegrated (charred, dismembered, or highly decomposed). And in order to prove identity you need a sample from the deceased’s maternal line. The down side to mtDNA is that it’s expensive to process and only a few labs do it. Also, persons with the same maternal lineage who are tested by mtDNA will not be distinguishable in DNA code from each other.
Nuclear DNA (nDNA)
What is it?
Nuclear DNA is the form of DNA found within the cell in the nucleotides creates by the 23 chromosomes from mom and dad.
How is it used to solve crimes?
Nuclear DNA is sometimes called touch DNA. This is the kind you hope to find at the crime scene in the form of blood, urine, semen, saliva on a cigarette butt, or glass.
Artificial DNA (aDNA)
What is it?
Artificial DNA was first engineered in Tel Aviv in 2009. Amplified DNA cells was mixed with DNAless red blood cells to create fake blood. And it fooled the American labs. Looks like we’ve come a long way since the days of corn starch, food coloring, and syrup. All you need is a sample DNA from anyone or a DNA profile from a database. There are currently two processes for manufacturing fake DNA. One is called whole genome amplification and the other is a cloning process So far current forensic testing has failed to tell the difference between nDNA and aDNA.
How is it used to solve (or commit) crimes?
Now, your high tech criminals, or even those with just some college-level knowledge of genetics, can engineer a crime scene or sell aDNA on the black market to other criminals. Want justice to be served in this case? A prosecutor can now contest the reliability of biological versus artificial DNA and save the case if he thinks the perp was faking it. Or a defense attorney can try to get DNA evidence thrown out if he believes someone planted fake DNA evidence against his client.
Y Chromosome DNA
What is it?
A Y Chromosome refers to a sample that contains only a male DNA sample. A YSRT is a testing method that extracts only the Y chromosome in order to identify a male presence in the sample being tested.
How is it used to solve crimes?
YSRT is used in cases of gang rape to prove multiple Y chromosomes or when there isn’t much male DNA present. YSRT testing is more rare and few labs do it. There is no organized Y chromosome database maintained in the U.S.
Familial DNA
What is it?
Not every single arrested criminal has their DNA listed in the CODIS database (run by the FBI). Since that is the case, a familial DNA search allows DNA from the scene of a crime to be run through CODIS and if there is a partial match (15 loci points) that would indicate that a relative of that criminal left DNA at the crime scene. With this information, law enforcement can now pinpoint a more specifical branch of potential suspects through their family tree.
How is it used to solve crimes?
In extreme crime cases, law enforcement officials can seek requests to use familial DNA searches in order to match DNA from a scene of the crime (or victim) to suspect’s family members. It has become more accepted practice in the U.S. after the 2010 Grim Sleeper case in California. It’s still rare to use familial DNA and only 12 states allow it under these circumstances: the case must be a cold case, an extremely violent crime, and investigators must have exhausted all leads and means.
DNA Fingerprint
What is it?
Each person’s DNA contains a slightly different code. The code is found in the way the bases are arranged. Remember the bases? Adenine, Thynine, Cytosine, and Guanine? So, the way in which these pairs (A-T and C-G) are arranged along the double helix creates your unique DNA fingerprint. And this is fingerprint can be replicated and used to make matches. A DNA fingerprint is also called DNA typing, DNA blue print, or a genetic profile.
How is it used in crime solving?
In all humans 99.9% of our genomes or DNA looks exactly the same as everyone else’s. It’s that 0.1% that tells us apart. When trying to make DNA matches, technicians look for 21 different loci (or regions) on the human chromosome. And it’s not uncommon that a majority of these 21 loci look the same from one person to the next. According to a LA Times article from July 8, 2008, “Although a person’s genetic makeup is unique, his genetic profile — just a tiny sliver of the full genome — may not be. Siblings often share genetic markers at several locations, and even unrelated people can share some by coincidence.” We’ve been trained by CSI to rely on the absolute validity of DNA evidence. But in reality DNA evidence can get stuck on boggy soil of doubt; thereby providing fertile ground for storytelling twists.
Now, we’ve covered the basics. In Part 2 we’ll take a look at other aspects of DNA identification… like fire and DNA… water and DNA… DNA versus fingerprints… and the new DNA ancestry detectives! And we’ll take a look at a new technology that traces smudges of microbes you leave on your phone… a world beyond DNA and fingerprint identification!
