DNA PROCESSINGMike McCutcheon

DNA DNA, or Deoxyribonucleic Acid

DNA is examined from the cell nucleus DNA is the building block for all life and is

unique for every person. Nearly every cell in a person’s body has a

nucleus The nucleus has 23 Chromosomes

100,000 genes in these chromosomes Four chemical bases of DNA: Adenine,

Guanine, Cytosine, and Thymine. G always pairs with C A always pairs with T Over 3 billion base pairs

DNA from Crime Scenes

DNA evidence can include: Blood, saliva or saliva stains, liquid

semen or semen stains, vaginal fluids, fingernails, hair (with root), skin cells, fingerprints, nasal and ear secretions, bones, sweat

In other words, DNA is everywhere. You must know where to look for it and how to

preserve it

DNA History

First report in 1868, but the structure was discovered in the 50’s

In 1984, Alec Jefferies, was able to map out DNA so that it could be compared to other samples

Restrictive Fragment Length Polymorphism (RFLP) was created and could discriminate to the certainty of 1 in 5 million

The problem was a large undegraded sample was needed Because each cell only has one nucleus

DNA History

Polymerase Chain Reaction (PCR) was developed to solve the problem of needing a large sample The scientist was able to copy the DNA

structure creating enough genetic material to be tested

It allowed for much smaller samples, but he the statistical discrimination was much lower than the RFLP

Some times the discrimination was not enough to make individual characteristics

Current DNA Analysis

Short Tandem Repeat (STR) Similar to the multiplication of the DNA in PCR,

but with a much higher discrimination rate 1 in 6 billion

Saliva from licking a postage stamp has enough DNA material to make a distinct individualization

Proper Evidence Collection and Storage

In order for a lab to successfully examine DNA evidence, it is imperative that the samples be collected and stored properly.

Examples: Gloves, Tyvek suits are a must, not a suggestion Use sterile water Air dry Druggist fold Use polyester swabs instead of cotton swabs Properly packaged Use adhesive tapes

DNA Analysis

DNA can tell us many things: Remember, it is only as good as what you

can compare it to Great care must be made to ensure that

the sample is well protected.

mDNA

Mitochondrial DNA is not the same as DNA Mitochondria are organelles that are in

each cell. The organelles exist in more numbers in each

cell mDNA is inherited only from the mother

It can be compared to any female relative For example: Hair from a decomposed

body can be compared to the mDNA of living relatives to see if there is a match

DNA needs the hair root. mDNA does not

Future of DNA Testing

Has come a long way. DNA can be extracted from a fingerprint

What is called “touch DNA” Rapid growth of DNA databases through

CODIS Many states require those

arrested/convicted to submit DNA to the CODIS database

Sources

http://www.newenglandinnocence.org

http://www.nij.gov

Gardner, R. (2012) Practical Crime Scene Processing and Investigation. 2nd ed. CRC Press

http://www.guardian.co.uk