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Y.Martinez, LSHS, 2014

DIRECTIONS: COPY NOTES IN ORANGE.

What is DNA profiling?What is DNA profiling?DNA profiling is the use of molecular genetic methods to DNA profiling is the use of molecular genetic methods to

determine the exact genotype of a DNA sample in a way that determine the exact genotype of a DNA sample in a way that can basically distinguish one human being from another. can basically distinguish one human being from another.

The unique genotype of each sample is called a The unique genotype of each sample is called a DNA profileDNA profile..

How do crime scene How do crime scene investigators create a DNA investigators create a DNA

profile? profile? 1. Evidence is collected at the crime scene:1. Evidence is collected at the crime scene:

Blood Tissue Semen

Urine HairTeeth Saliva Bone

2. DNA is extracted from sources at the crime scene and from victim and suspects

3. DNA samples are processedSample Obtained from

Crime Scene or Paternity Investigation Biology

DNAExtraction

DNAQuantitation

PCR Amplificationof multiple (STR) markers

Technology

Separation and Detection of PCR Products

(STR Alleles)

Sample Genotype Determination

GeneticsComparison of Sample

Genotype to Other Sample Results

If match occurs, comparison of DNA profile to population

databases

Generation of Case Report with Probability of Random

Match

4. Crime Scene Investigators search in areas of the genome that are unique from individual to individual and are “anonymous” (control no known trait or function)

The areas examined are Short Tandem Repeats or STR’s

Humans are 99.9% so…Humans are 99.9% so…

STR region

To determine the To determine the genotype (DNA profile) genotype (DNA profile) Crime Scene Crime Scene Investigators make Investigators make billions of copies of the billions of copies of the target sequence using target sequence using PCR.PCR. Starting DNA

Template

5’

5’

3’

3’

Target DNA

What’s the point of PCR?What’s the point of PCR? PCR, or the polymerase chain reaction, makes copies of a PCR, or the polymerase chain reaction, makes copies of a

specific piece of DNAspecific piece of DNA

PCR allows you to look at one specific piece of DNA by making PCR allows you to look at one specific piece of DNA by making copies of *only* that piece of DNAcopies of *only* that piece of DNA

PCR is like looking for a needle in a haystack, and then making a PCR is like looking for a needle in a haystack, and then making a haystack out of the needlehaystack out of the needle

Exons and IntronsExons and Introns*When DNA is made, exons and introns are made.*Exons are parts of DNA our body uses for everything!*Introns are non-coding regions of DNA or “Junk DNA”

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Suspects are Suspects are includedincluded in an investigation if in an investigation if their DNA profile matches with genotypes their DNA profile matches with genotypes found at the crime scene.found at the crime scene.

Suspects can be Suspects can be excludedexcluded if their DNA profile if their DNA profile does not match genotypes found at the crime does not match genotypes found at the crime scene.scene.

DNA profiling is never used alone; it is used in DNA profiling is never used alone; it is used in combination with other evidence. combination with other evidence.

What happens What happens during PCR?during PCR?

The PCR ReactionHow does it work?

The process occurs in a machine called a Thermalcycler.

The Thermalcycler will go through a series of heating and cooling to activate enzymes and denature DNA.

In about 3 hours, over 1 BILLION of copies of the desired gene is replicated.

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