Familial DNA: An Unusual Way for Your Inspector to Find the Perp - Information for Writers

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I was recently chatting with David Swykert about some of the stories he'd come across while at work as a 9-1-1 operator. He introduced me to a new concept, familial DNA.

First, David, would you please introduce yourself?

David - 

I am a retired 911 operator living in northern Kentucky. I also worked as an operations manager for a large transportation company and as part of my job investigated accidents. I worked as an emergency operator for the Department of Public Safety in northern Michigan until 2006. I have written in several different genres, mystery, romance, and even some literary, short fiction and novels. I have five published novels.

Fiona - 

How did you first learn about familial DNA in crime cases?

David - 
I first heard about Familial DNA from the officer that was our CSI for our department. It's simply a DNA search that turns up no exact match, so you ask the computer for the closest match.

Fiona -

If you need a quick brush up on DNA in crime scenes go HERE

So the DNA found at a scene that did not match any of the DNA that was in the computer bank. The officer would then task the computer to find as close a match as possible, hoping to find the general family from which the possible perpetrator belonged. Is there precedent for this?

David - Yes. Lonnie David Franklin, deemed The Grim Sleeper, because of the length of time in between murders committed by him. There was never any DNA at any of the crime scenes that identified Franklin. 

The investigators found him by running a Familial DNA search which turned up his son, who was a convicted felon. This led the investigators to Franklin. 

After Franklin's arrest, the investigators tested Franklin and his DNA was a match with that found at the crime scene. 

He was caught the summer of 2009. But this case is just going to trial perhaps this year (2014). There have been volumes of appeals and briefs filed because there was never any direct evidence that connected Franklin to the crimes, and defense lawyers contend his investigation based on someone else DNA was a violation of his Fourth Amendment rights concerning illegal search and seizures.


The argument is: the inspectors had no direct evidence that connected Franklin to the crime before they investigated him.

When you run a persons records, you have to have a law enforcement purpose that allows the search, the defense contended they didn't have one. 

The courts have ruled so far in favor of the prosecution, and the trial is moving forward. But it will get appealed to higher courts. The Fourth Amendment protects you against unusual search and seizure, but of course there can be very broad interpretations of what this means.

Fiona - 

What are the arguments against using familial DNA?

David - 
Civil Libertarians argue that using someone else's DNA to justify investigating someone else violates the Fourth Amendment that protects us against "unreasonable" search and seizure. They see this as "unreasonable." 

I really don't think an officer can "abuse" the technique. In defense, the lawyers can always ask to see who's DNA caused the detectives to investigate a defendant, discover whether that DNA close to the perpetrators, and ask about probable cause. 

Amazon Link

When I heard about familial DNA searches, I thought it would be a great hook for a crime story, which I wrote in early 2009 just before LAPD caught The Grim Sleeper using the technique.

I'm surprised crime writers haven't written a lot of books regarding the use of the technique. In mine, they catch him, but the D.A. isn't sure they can prosecute him successfully, which causes my detective, Bonnie, a lot of consternation. She knows he did it, but perhaps he can't be convicted. Which could happen out in LA. That's just getting started.
Fiona - 
Let's talk about your book. Can you give a synopsis?

David - 
This is a fictional story about Detroit Homicide Detective Bonnie Benham, who convinces the District Attorney to allow a Familial DNA search as she investigates the murder of several young girls. 

The book reveals standard investigative homicide procedures and the frustration of the officers as all leads go nowhere and the body count continues to mount. A task force is put together and Bonnie and her partner, Neil Jensen, who understands Bonnie’s frustration, become inseparable as they track this killer of children.

Fiona - 
I had never heard of familial DNA prior to your book, while it will probably be more prominent as the trials catch the imagination of writers. If a writer wants to include this twist in their plot line can you give us any more information about the process?

David - 
It's no different than a DNA search, except the lab expands the search to include DNA that is close to the DNA profile from the crime scene. The investigators then investigate the people the expanded search includes. 

Last time I checked there were only two states in the U.S. that even have a policy regarding it's use, Colorado, and California, Michigan, where my story is set, is not one of them. 

What I thought would be the hook for my story is the old: I know he did it, but I can't prove it. It took from 2009 until this year for the courts to get The Grim Sleeper into a courtroom, and this case will perhaps set precedence for the future use of the technique. I think the rest of the states are waiting to see the outcome before they write a policy.

Fiona -
What do you hope the outcome will be?

David - 
I want to see the guilty convicted. DNA profiling has worked both ways, it's freed a lot of innocent people. As unique as DNA is, I would hope the courts decide if the DNA is close enough to a match this constitutes a reasonable search. 

I'm not an expert on the scientific profiling of DNA, but I would think they can set parameters that the profile must meet, a standard, which when met, allows indicates that it is reasonable to investigate this person. 

I believe ultimately the courts will allow its use. Fingerprinting isn't absolute, and they allow it entered as evidence. So there is already precedence.

Fiona - 
David, thank you so much for chatting with us today - I can almost hear all of the cogs starting to whir in the minds of mystery writers.

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Forensic Trace Evidence: Hair and Fur - Info for Writers

 (Photo credit: Wikipedia

So your investigator arrived on the scene.
(Crime Scene 101 for writers article)

They've photographed and collected all of the macro-evidence. 

Now they need the trace evidence (that which isn't easily seen with the naked eye) collected and processed. This trace evidence might include hair. 
* Hair is one of the most collected forms of trace evidence.
* Hair is particularly useful because it is stable over time.
* Because hair is produced around blood vessels it is a long term
   record of toxins
   ` Illicit drugs such as THC in marijuana
   ` Poisonings such as arsonic
   ` Heavy metal exposure such as lead.
   ` Medications
* Hair grows at a fairly predictable rate of about .5 inches per
   month. So scientists can even calculate when the exposure to
   the toxin began - depending on the length of the hair.

Investigators will use three basic means of collecting hair and other trace evidence.

1. Hunt and peck
2. Tape
3. Vacuum
Video Quick Study (9:50) Prt 1 
Video Quick Study (1:54) Prt 2 Teacher explaining collection
                     methods of finding trace evidence including hair. 

Humans have various hair all over their bodies including body hair, eyelashes, and eyebrows. But only head hair and pubic hair have forensic use.

So let's say we have a rape victim. They find hair on her clothes. 

1. They will have to collect hair from the victim - this is a known or

    K sample

2. The laboratory will compare the victim K sample to the 

    Q sample - the sample in question.

    a. First, they will figure out if the Q sample is a human hair.

    b. Second, They will determine if the K and Q samples have

        the same general characteristics.

Let's say that the victim K sample excludes the Q sample that is they could not come from the same person. But our investigators have their eye on a bad-guy. They ask him for hair samples. He can 

a. Agree and submit to testing

b. Refuse - if he refuses then the courts can order him to submit.

The suspect K sample is collected.

1. It is suggested by the FBI that 100 full, intact strands, including

    the follicle are harvested from the suspects head from various

    regions as even hair from an individual person can differ

    from region to region on their heads.

2. It is suggested that at least 20 intact strands of pubic hair are

    obtained.

*If the laboratory says that the suspect K sample and the Q sample

  do not share similar qualities, this excludes the suspect. 

*If the lab says that there are similarities in the K and Q samples,

  this DOES NOT mean that you found your villain. 

* Hair is class evidence - it can be used to exclude but not to prove

   someone is culpable.

* If there are similarities, the sample is sent for DNA testing.

  (DNA 101)

* By doing lab analysis first, it saves a great deal of time and money

   over going right to DNA analysis

Let's do a little biology 101 - I know you're excited!

(Photo credit: Wikipedia)

* The root of the hair is

   anchored into the dermis of

   the skin

* Follicles are surrounded by
   epidermal cells
* Blood vessels at the roots
   deliver nutrients

Looking at the hair itself

* Hair is mostly made
   from keratin

 (Photo credit: Wikipedia)

* The outside of the hair is 
   called the cuticle. 
* In humans, the cuticle
   gives very little information. 
* Mammals have various
   patterns in their cuticles and
   the labs can compare the
   various patterns to tell
   that's a bat, or a rabbit, or a
   werewolf. 

* Inside of the cuticle is the cortex.
* The cortex is the thickest layer of the hair strand.
* This is where pigment from the melanin can be found, giving hair
    its color.
   ` Hair colorant can coat the surface or penetrate to the cortex.

   `In bleached hair pigmentation is lost from the cortex
   `Only the hair that is treated will show a change in color, so at the
     root the true color will be visible. There will be a line of 
     demarcation between the two

* When people change the color of their hair, or their hair changes
    naturally as the subject ages, this can create issues in finding 
    similarities in the K and Q samples. 
* PLOT TWIST!
   A fingerprint cannot be altered, but your villain can thwart an
   investigator by dying their hair, committing a crime,
   and then dying their hair a different color. So even if the police
   take K samples from their hairbrush they will not show as similar
   in the lab. And when they take them from hair that's been altered
   it too will not show as the same.

Pubic Hair Medulla (Photo credit: Wikipedia)

The Medulla

* The medulla is at the core of the hair sample

* It is the hollow region at the center.

* A data bases of medulla patterns have been developed to

   identify various animals and differentiate human from other

   animal hair.
* Finding animal hair can be very helpful. It can link transferred
   hair from a suspect at a crime scene. For example, Blade Slayer
   goes in and attacks your heroine. Trace evidence hair is found.
   It's a black rabbit, and Blade Slayer happens to have a black
   rabbit named Cuddles. It's circumstantial, but it can be helpful.
* Animal hair forensics can also be used in crimes like poaching
   and illegal animal importation (Wildlife Forensics Blog Post)

Three Phases of Hair Growth

Anagen Phase - 
* 2-7 yrs for scalp hair 
* Growth phase where cells are formed at the root which pushes the
   hair out of the scalp making the hair longer.
* This hair will only fall out if it is yanked out.
* When hair from this phase is

Animation of the structure of a section of DNA. The bases lie horizontally between the two spiraling strands. (Photo credit: Wikipedia)

   found at the crime scene it has a
   follicle attached. 
* The follicle contains DNA that
   will identify an individual
Catagen Phase- 
* The hair is in transition
* The hair no longer grows, the
   cuticle pulls away
Telegen Phase - 
* The final phase where hair falls
   out.
* In the catagen and telegen
   phases the follicle is no longer
   attached to the hair. Nuclear
   DNA cannot be found. The
   investigators will try to test for
   mitochondrial DNA in the hair
   shaft. Mitochondrial DNA is not
   conclusive as everyone in the
   matriarchal line will have the
   same DNA (DNA 101 for Writers)
* Telogen hairs are those typically found at crime scenes.
* Because hair is easily transferred from one place to another, it is
   circumstantial evidence.

What else can an investigator tell from a hair strand?

* Pubic hairs have shaft differences along the length and a

   continuous medulla

* Male facial hair is usually more triangular in shape
* Hair that's been cut or shaved will have a blunt end
* Hair that is allowed to grow naturally such as arm hair will have a
   naturally tapered end
* Head hair - not recently cut- will show a frayed or split end
* Age cannot be discerned.
* Sex cannot be determined.
* Ethnicity - is difficult. The person would have to have a very
   clean background as Caucasian, African, or Asian ancestry.
   And then, there are variables that can point the investigators
   in a direction. It is not conclusive.

So what can an investigator say about a hair sample?

* Is it human, or animal (or vampire)?

* Is it a useful sample, either head or pubic hair?

* Is it head or is it pubic hair?

* Is the Q sample consistent with the K sample?

   `If yes, further investigation - suspect stays in the pool.

   `If no, suspect is removed from possibilities; they look for another

    suspect.

   `If yes AND no that is there are similarities AND differences,

    then no conclusion can be drawn.

Video Quick Study (4:16) Hair testimony at Casey Anthony trial

Video Quick Study (4:27) Britain CSI school

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Skeletons in Her closet: The Forensics of Skeletons for Writers

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I curled up like a cat on Miriam’s living room couch with a cup of hibiscus tea steeping on the table beside me. Miriam was on the phone with the police, jotting notes about a case they wanted her to work for them. Someone’s Great Dane came home this morning with a human skull in his mouth. The detective needed a jump-start – some information to get going with while the skull waited its turn on the forensics lab shelf. ~ WEAKEST LYNX










Writers, if your crime scene includes skeletal remains or even remains that have advanced to a soupy mess, the person who is called in to take control of the bones is a FORENSIC ANTHROPOLOGIST.
***NOTE: The forensic anthropologist is applying their post graduate studies in biology and anatomy as well as their understanding of trauma to research the bones. They do not solve the crime. They do not interview suspects or witnesses (LINK to Interrogation for Writers). They simply: study, document, report, testify (where necessary).

Forensic anthropologists can help identify skeletonized human remains, such as these found lying in scrub in Western Australia, circa 1900–1910. (Photo credit: Wikipedia)

Forensic Anthropology - Dem Bones!
Video Quick Study (3:13) Tanya Peckmann talks about her job.

Servicemembers search for POW/MIAs on Wake Island Greg Berg uses a sifter to look for bone and artifacts at a dig site Jan. 12 on Wake Island. Mr. Berg, a forensic anthropologist, was sent to do a site survey after Wake Island officials notified the Joint POW/MIA Accounting Command of bones located on the island. JPAC officials are charged with achieving the fullest possible accounting of all Americans missing as a result of past conflicts. (U.S. Air Force photo/Tech. Sgt. Shane A. Cuomo) (Photo credit: Wikipedia)

The job of Forensic Anthropologists is to make some determinations concerning the skeleton that was discovered or exhumed. They are called in by officials to remove the remains.
* Remains are placed in a body bag for transport to a
   forensic laboratory.
* The remains are reconfigured to a supine position, and
   photographed.
* Any remaining soft tissue is cut away from the skeleton
* The bones are abraded with steel wool to remove dirt,
   bugs, and soft tissues.
* The bones are then soaked in a chemical solution to
    further clean and prepare them for examination.

This Video Quick Study (12:04) is a non-narrated look at a forensic anthropologist team at work





The Forensic Anthropologists attempt to make the first sets of identifying data:
* Approximate age

FAFG - coded corpse (Photo credit: xeni)

* Sex
* Size/height
* Ancestry

AGE:

* Teeth and bone growth help to identify the proper age.
* Precise age determination is easier in children than in adults because of the statistical probability of various
   developments taking place in teeth and bone fusion/growth plates.
* Age results for adult remains are given in broad ranges.
* 206 is the average number of bones of an adult.
* An adult  skull has approximately 22 bones.

Parts of a long bone (Photo credit: Wikipedia)

* A newborn skull has approximately 44 bones.
* In assessing age in children, the long bones of the body
   show dramatic changes with age.
*ossification of the growth plates follow general
  standards:
  - First growth plates close at the elbow
  - next ankles, knees, hips, then shoulders.
  -  The last growth plate to close up is the central tip of
     the clavicle around 23-28. (health and nutrition
     effects this age span)

Video Quick Study (1:48) - bone changes from infancy to adult

   * Teeth form from crown to root.
   * At birth primary teeth are already present in the jaw.
   * At 6 mos most infants have visible teeth.

Video Quick Study (3:17) Dr. Snow identifies Gacy's
                                        victims by age.

. (Photo credit: Wikipedia)

SEX:

* Prior to puberty, the skeletal remains cannot

   be identified as male or female without DNA.

* A pelvis in a female is wider from front to back.
* Joints tend to be larger on males.

THE SKULL - this information is statistically correct. Measurements are made and compared at different points on the skull to determine a statistical probability rather than a 100% certainty.
* Male occipital protuberance is larger to attach larger
   neck muscles.
* Male brow ridges are larger
* Women tend to have higher smoother foreheads.
* Male jaws tend to be at a 90 degree angle with
   squared corners.
* Women's jaws tend to be smoother with
   pointier chins

Video Quick Study (2:35)

the adult skull is normally made up of 22 bones. Except for the mandible, all of the bones of the skull are joined together by sutures, semi-rigid articulations formed by bony ossification, the presence of Sharpey's fibres permitting a little flexibility (Photo credit: Wikipedia)

SIZE AND HEIGHT

* Is best identified from a full skeleton.
* Statistics have been developed to allow a range based on skull size.

the adult skull is normally made up of 22 bones. Except for the mandible, all of the bones of the skull are joined together by sutures, semi-rigid articulations formed by bony ossification, the presence of Sharpey's fibres permitting a little flexibility (Photo credit: Wikipedia)

ANCESTRY

* Without DNA ancestry is difficult.
   LINK to DNA article

* DNA is best harvested from the teeth, though it is

   possible to extract from bone.

* Skull structure yields the biggest clues about

   race/ancestry based on math formulas.

* Few people today come from a racially pure

   ancestral line, making identification more difficult.

* In order to apply the statistics to ancestral

   identification, a fairly intact skull is required.

Skeletons under excavation at Walkington Wold (Photo credit: Wikipedia)

Beyond excavation (LINK to Crime Scene Info for Writers), and the preliminaries of age, sex, size and ancestry, a forensic anthropologist can offer investigators other identifying information:
* History of bone breakage
* History of surgical interventions such as ACL replacements and other injuries where screws and implants
   were used.
* Nutrition over the life span
* Toxicity over time such as arsenic or mercury.
* Exposure to heavy metals like lead

* They can also help determine the number of skeletons in a mass destruction such as a large fire or plane
   accident.

They can inform and testify about stab wounds and what type of weapon might have been used through trauma analysis.
* Was the break:
   - antemortim trauma - before death like healed fracture or screws from surgical repair.
   - post mortem trauma - what happened to skeleton after the death - like an animal
   - perimortem trauma - bone damage at or around the time of death, such as  a broken jaw or cracked
     skull.

To gather this information they use CAT scans, and other medical diagnostic machinery.
Video Quick Study (3:51) Discusses high-tech tools.

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Walking Through Forensic DNA Basics: Information for Writers

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 (Photo credit: Wikipedia)

This week I had the opportunity to go down to Richmond to visit the FBI headquarters. A handful of Sisters in Crime Members were being hosted by the FBI Evidence Response Team. I want to thank the team for sharing their expertise. (Names and images are withheld for security purposes)

That night I learned a lot about processing the scene of a crime, collecting everything from foot prints BLOG LINK - Footwear Evidence to  fingerprints BLOG LINK to Fingerprint Evidence to fibers.

But the gold star belongs to DNA. DNA has risen to be THE  best available evidence because the laboratory results are statistically linked to a single person and exclude all others.

Did you know that with the improvements in science, they can now trap enough DNA in a fingerprint to create DNA profile?

If you are writing a story that involves a crime, it's likely that your investigation team will be looking for DNA to collect and use to solve the case.

Processing Blood Samples, FBI

Forensic analysis of DNA can be confusing so let's walk through this together.

STEP ONE - What Is DNA? 

First the bilology basics. I know. I know. It's the spinach on your plate. But it's important, so I'll try to make this as quick and as painless as possible.


DNA - Deoxyribonucleic Acid -
* All cells have DNA (except red blood cells)
* DNA is the genetic material making up our chromosomes
* Gene – the basic unit of heredity; a sequence of DNA nucleotides
   on a chromosome.
* Genome – the sum total of an organism’s genetic material.
* DNA encodes the instructions for when and how to make
   proteins. These proteins tell the cell how it will
   function - is it a brain cell? a liver cell?
* It looks like a twisted ladder. The uprights are made out of
   phosphates and sugars. rungs are pairs of
   smaller particles called nucleotides.


You're doing great! Hang in there!

(Photo credit: Wikipedia)

* All DNA is made up of a combination of four letters
  G - Guanine
  C - Cytosine
  A - Adonine
  T - Thymine
* G and C got together A and T go together

Mitosis (Photo credit: id-iom)

Mitosis -
* DNA replication
* A cell splits by dividing like a zipper
* The new cells contain an identical set
   of cells as were present at conception
* This only changes when there is a
    random mutation
* All cells in the whole body contain the
   exact same DNA

Video Quick Study of Mitosis (1:29)
VIDEO QUICK STUDY (8:03) basic info on DNA and Mitosis - might be more information than you need, but the presentation is thorough and easily understood.


STEP TWO - There Are Two Kinds of DNA

 (Photo credit: Wikipedia)

Nuclear DNA-
* It is found inside the nucleus packed
   into chromosomes
* It is inherited from both parents
   50% from our mom and 50% from
   our dad.
* Each parent contributes 23
   chromosomes for a total of 46.
* The dominant and recessive qualities
   gives us our traits
* A DNA profiles belongs to an
   individual and ONLY that
   individual and no one else in the world    UNLESS we have an
   identical twin. Plot twist!
* The closer we are in genetic
   relationship to someone else, the
   closer the DNA configuration.
* Each cell has one copy of nuclear DNA


Mitochondrial DNA-
* Is found in mitochondria
* 100% of mitochondrial DNA is inherited from mom.
* The mitochondrial DNA is the same in our brothers and sisters
    regardless of who fathered each child.
* All mitochondrial DNA came from your mom which came from 
   your mom's mom which came from your
   mom's mom's mom etc. How cool is that?
* Is not housed in a a set of chromosomes
* This DNA is smaller than Nuclear DNA
* This DNA is present in larger numbers than Nuclear DNA
   (nuclear DNA has just one copy per cell)
* This DNA tends to be more stable than Nuclear DNA over time.

VIDEO QUICK STUDY (1:58) Two Minute Science Lesson: How DNA Testing Works

STEP THREE - Collecting DNA Evidence

Maryland V. King Police can collect DNA without a warrant Video Quick Study (1:55)

Biological evidence is perishable
* DNA will fragment
* The best shot at getting useful DNA is in a fresh sample
* Fresh tissue has more nuclear DNA and an older sample has less

Things that cause DNA to degrade
* UV light
* Acid
* Bleach
* Hydrogen Peroxide
* High humidity
* Heat and Fire
* Anything that oxidizes biological molecules


Handle with Care:
Video Quick Study (2:16) Mentions the changes in technology and the importance of properly preserving the sample.

* If the evidence that is being collected is wet it should be air dried.
* The evidence should be stored in a PAPER BAG that can release
    moisture
* Store in low temperatures (this prevents bacterial or fungal
   growth that has its own DNA)
*  Avoid as much as possible environmental contamination.

Crime Scene Techs:
* Need to understand that they can be contaminated by the crime
   scene (pick up bacteria etc.)
* Can contaminate a crime scene with their own saliva, dander, hair
   etc.
* The FBI Processing unit that I visited this week uses full Tyvek
   suits to prevent contamination of the scene.
* People who were on the scene will often be asked to give a DNA
   sample called an "ELIMINATION SAMPLE"
* Most often reference samples are taken from a buccal swab. A
   square piece cotton is swabbed over the
   inner cheek. This is placed in an envelope. Why not a vial?
   Because a closed container encourages the
   growth of other life forms. 
   VIDEO QUICK STUDY (3:07) How to collect a buccal sample.
* DNA elimination samples are collected from victims and
   witnesses etc.

. (Photo credit: Wikipedia)

PLEASE NOTE this elimination sample does NOT get run through the system. It is merely there for the scientists to compare with the sample they are analyzing. Your character will NOT be located and charged with a previous crime. There are all kinds of privacy laws that prevent this from happening, according to the FBI agents we were interviewing.


Death Investigators: What if you have a body to identify?
If the investigators have an idea who this might have been they can get a swab from a blood relative and try to find markers that they share. If no relative is available, then they could go to the person's home and try to collect DNA there from a toothbrush or razor, etc.

What if the house burned down and DNA from that location is not available? Well, investigators could try to find stored DNA samples, for example a woman's pap smear might be stored or perhaps your character had given blood to the Red Cross.

Here's a VIDEO QUICK STUDY (6:09) that gives a simplified description - good overview. 
STEP FOUR - Extracting and Processing DNA

Extracting DNA isn't hard you can do it right now in your own kitchen. Don't believe me?
Video Quick Experiment for You to Try (2:46)
Video Quick Study - Separating DNA from Blood (6:37)

In extracting DNA from Crime Scene or reference samples, the goal is to find the 1% that differs from everyone else. This gives an individuals DNA Fingerprint or DNA Profile.

99.9% of our DNA is the same in all humans. Only .1% differentiates us

* DNA is stiff and brittle. In order to avoid damaging it, a
   technique is employed that breaks down the cell around it.
* In a crime scene laboratory being meticulous is paramount.
* VIDEO QUICK STUDY - (6:19 - but go right to 3:00 mark) this
   process is better explained through this video than writing the
   steps because of the equipment

IF YOU ARE WRITING A BOOK THAT TAKES PLACE IN THE 80s OR 90s use RFLP:

RFLP Analysis - Restriction Fragment Length Polymorphism not widely used since the mid-90s
* A large sample is required
* Results are not compatible with major DNA databases
* The proces uses molecular scissors to cut where a TA next to a
   CG combos. Since everyone has different DNA profile's the
   material created will be of different lengths. (15-35 repeating
   base pairs)
* This is then processed with Gel Electrophoresis
   Video Quick Study (5:18) Frankly this is the quickest, easiest
   way of understanding the process

To correct the problem of sample size, scientists developed PCR - Polymerase Chain Reaction
* This was developed in 1983 as a method for replicating DNA
* VIDEO QUICK STUDY (3:32) sorry this has no audio, but it is
   the best quick study I could find
* PCR takes advantage  of the DNAs double strand and its simple
   code
* Uses a thermocycler to double the amount of DNA with every
   cycle.
* Only one strand of DNA can make a billion copies in four hours

IF YOU ARE WRITING A BOOK THAT TAKES PLACE AFTER Mid-90s use STR:

STR - Short Tandem Repeat
* It still uses PCR to make copies
* STR focuses on the smaller repeating units in DNA
* STR uses only about 3-7 repeating base pairs (where RFLP
   needed 15-35)
* Can be used on much smaller samples than RFLP
* Can be used on more degraded samples than RFLP
* Only 18 cells are needed to get a DNA profile - this is why they
   can pick up DNA from a fingerprint, according to our FBI
   instructor.
* Uses Capillary Electropheresis -  done in a column (not in a flat
   gel as in electrophoresis)

THERE ARE 13 DIFFERENT CORE LOCATIONS WITHIN DNA that captures most of humans variability in STR

CODIS FBI Logo (Photo credit: Wikipedia)

* Each core location has its own
   established probability of being
   found in the larger population.
* When all 13 different probabilities
   are added together the statistical
   probability are in the quadrillions.
* These can be put into the CODIS
 (Combined DNA Index System)
  developed by the FBI in the late
  90s. Pay attention to this date if
  your story happens before this time
  period.


Recently they've developed a way to tell if the DNA comes from a man or a woman by looking at the sex chromosomes. (XX or XY) They do this by looking at the amelogenin gene on the sex chromosome. It is longer in a man than woman but this is enough to tell the difference. This is important because sometimes there is a mixed sample of DNA, for example if they do a vaginal swab for sperm.


STEP FIVE - Is It a Match?

Reading the computer output is outside of the scope of this article - though I will address this in the near future.

CODIS 13 point profile (Photo credit: Wikipedia)

The information gathered is analyzed and a statistic is assigned.
* Population Genetics gives us
    statistics about the likelihood of this
    profile occurring in a population. It is
    a PROBABILITY that the same
    profile is replicated in the population
    and not coincidence.
* The more stretches of DNA that are
   compared between two people the
   statistics possibility of error narrows.
   It can become so narrow that it
   EXCLUDES everyone
   else from the pool of possibilities
   EXCEPT an identical twin.




Okay how was that? Not bad right? We made it to the end of the DNA pathway. Now as you sit on the bench to catch your breath, let's review some points at which a plot twist could mess everything up:

* Has the prosecution kept tight control of its chain of who has
   custody from collection to end result?
* Was the biological material from which the DNA was extracted
   identified? For example, in a rape case was it semen that is being
   identified?
* Is the testing laboratory accredited?
* Has the testing laboratory  been audited by an outside agency?
* Has the testing laboratory  undergone a proficiency test - and was
   it a blind test?
* Did the laboratory run the required control samples?
* Was there examiner bias? Did the tech talk directly to the
   investigator or was it blind?
* How large was the DNA sample? Was it from a pool of blood?
   Or was it from a fingerprint?
* What if your character -- either victim or accused -- has a relative
    involved in the research (or an ex-wife eek!)?
* Was more than one DNA profile mixed in the sample?

So many ways to play with DNA evidence! 

EDIT 

Intermountain Forensics:

This is very good! If we could add to your collection: CODIS Core Loci is now 20 markers and keep an eye out on next generation sequencing and genetic genealogy for the future of forensic DNA. Nice work!

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