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DNA Fingerprinting. Dna basics. Forensics Uses. DNA evidence has been used to investigate crimes, establish paternity, and identify victims of war and large-scale disasters. Science and the Law: the Implications of DNA Profiling. New York State to Exonerate Innocent Prisoners Using DNA.

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Forensics uses
Forensics Uses

  • DNA evidence has been used to investigate crimes, establish paternity, and identify victims of war and large-scale disasters

Science and the Law: the Implications of DNA Profiling

New York State to Exonerate Innocent Prisoners Using DNA

The Smoking Gun, 9/11 DNA Evidence Revisited

DNA Paternity Test – Worldwide Increase

Background information
Background information

  • Body consists of 60 trillion cells

    • Most of these cells contain a nucleus

      The exception = Mature red blood cells

    • Each nucleus contains the genetic material, or the directions, to make us who we are

      • The genetic material is found in structures called chromosomes

Where is dna found
Where Is DNA Found?

  • DNA is found in all nucleated body cells—white blood cells, semen, saliva, urine, hair root, teeth, bone, tissue

    • Most abundant in buccal (cheek) cells

  • Red blood cells have no nuclei; and therefore, no nuclear DNA

    • DNA obtained from blood comes from white blood cells

Background information1
Background information

  • Chromosomes are composed of little segments called genes

    • The gene is the fundamental unit of heredity

      Holds instruction for the body cells to make proteins that determine everything from hair color to our susceptibility to disease

  • Each gene is composed of a specific sequence of DNA


  • DNA stands for deoxyribonucleic acid

    • Blueprint, or directions, for all living things

    • Universal – found in every living thing

  • DNA is in the form of a double helix, or spiral ladder

Dna components
Dna components

  • DNA is made up of primary units called nucleotides

    • Each nucleotide is composed of three pieces

      Sugar (deoxyribose)

      Phosphate group

      Nitrogenous base

      • Four different bases: Adenine, Guanine, Thymine, Cytosine

Dna shape
DNA shape

  • The sugar and the phosphate group create the backbone of the molecule

    • This is the sides of the ladder

  • The bases are the rungs of the ladder

Base pairing rule
Base pairing rule

  • Each base matches up with one other specific base = base pairing rules

    Adenine will always bind to thymine, and vice versa

    Cytosine will always bind to guanine, and vice versa

  • Each DNA strand contains over 1 million base pairs

    • It is the order of bases that dictate your traits

Types of dna
Types of Dna

  • Nuclear

  • Found in the nucleus

  • Constitutes 23 pairs of chromosomes inherited from both parents

  • Each cell contains only one nuclei

  • Mitochondrial

  • Found in the cytoplasm

  • Is inherited only from mother

  • Each cell contains hundreds of thousands of mitochondria

  • Can be found in skeletal remains

Nuclear DNA is present in the head of the sperm. Mitochondrial DNA is present in the tail. At conception, the head of the sperm enters the egg and unites with the nucleus. The tail falls off, losing the father’s mitochondrial DNA

Nuclear DNA

Mitochondrial DNA

Historical information
Historical Information

  • James Watson and Francis Crick—1953 discovered the configuration of the DNA molecule

  • Alec Jeffreys—1985 isolated DNA markers and called them DNA fingerprints

  • Kary Mullis—1985 developed PCR testing

  • 1988—FBI starts DNA casework

  • 1991—first STR paper

  • 1998—FBI launches CODIS database

Dna typing dna profiling
DNA Typing (DNA Profiling)

  • Method in which DNA is converted into a series of bands that ultimately distinguish each individual.

  • Only one-tenth of a single percent of DNA (about 3 million bases) differs from one person to the next.

    • Scientists use these regions to generate a DNA profile of an individual.

Uses of dna profiling
Uses of DNA Profiling

  • To identify potential suspects

  • To exonerate individuals

  • To identify crime and casualty victims

  • To establish paternity

  • To match organ donors

Non coding regions
Non-Coding Regions

  • 3 percent of the human DNA sequences code for proteins

  • 97 percent is non-coding and is repetitive; repeating the same sequence over and over

  • 50 percent of the human genome has interspersed repetitive sequences

Dna typing fingerprinting
DNA TYPING“Fingerprinting”

  • Steps in the profiling process

    • PCR—Polymerase Chain Reaction

    • RFLP—Restriction Fragment Length Polymorphism

    • STR—Short Tandem Repeats

Pcr polymerase chain reaction
PCRPolymeraseChain Reaction

  • PCR  a technique used for making copies of a defined segment of a DNA molecule.

    • This can be valuable when the amount of evidence is minimal.

    • Millions of copies of DNA can be made from a single speck of blood.

Pcr the process
PCRThe Process

  • Heat the DNA strands, causing the strands to separate (unzip).

  • Cool the mixture and add a primer  a short sequence of base pairs that will add to its complementary sequence on the DNA strand.

  • Finally, add a DNA polymerase and a mixture of free nucleotides to the separated strands.

  • Repeat as needed


Each time the PCR process is completed, the number of DNA strands DOUBLES

Process is typically repeated 25-30 times

PCR Virtual Lab

Rflp restriction fragment length polymorphisms the steps
RFLP—Restriction Fragment Length Polymorphisms:THE STEPS

  • Isolate—separate DNA from the cell; use copies made from PCR

  • Cut—using restriction enzymes to make shorter base strands

    • Restriction enzymes cut DNA into smaller fragments at very specific locations

  • Sort—by size using electrophoresis

  • Analyze—the specific alleles for identification



A technique used to separate DNA fragments.

  • An electrical current is moved through a gel substance causing molecules to sort by size.

    The smaller, lighter molecules will move the furthest on the gel.

  • After developing, the fragments can be visualized for characterization.

Let's use RFLP technology to determine if Jack is the father of Jill's child named Payle.

In this scenario, DNA was extracted from white blood cells from all three individuals and subjected to RFLP analysis. The results are shown below:


Dna technologies: of Jill's child named Payle.



Short tandem repeats str
Short Tandem Repeats (STR) of Jill's child named Payle.

  • STR’s are locations (loci) on the chromosome that contain short sequences of 2 to 5 bases that repeat themselves in the DNA molecule.

    • Each parent’s STR can be different sizes

STRs of Jill's child named Payle.

  • The advantages of this method are that it provides greater discrimination, requires less time, a smaller sample size, and the DNA is less susceptible to degradation.

Short tandem repeats str procedure
Short Tandem Repeats (STR) Procedure of Jill's child named Payle.

  • Extract one of the possible genes found in the human genome that qualify.

    • Example: The gene TH01 has seven human variants with a repeating sequence of A-A-T-G

  • Amplify the sample by means of PCR

  • Separate by electrophoresis

  • Examine the distance the STR migrates to determine the number of times TH01 repeats

Short tandem repeats str1
Short Tandem Repeats (STR) of Jill's child named Payle.

  • Each person has two STR types for TH01—one inherited from each parent.

  • By continuing the process with additional STRs from other genes, you can narrow down the probability of DNA belonging to only one person.

Short tandem repeats str2
Short Tandem Repeats (STR) of Jill's child named Payle.

  • STR typing is visualized by peaks shown on a graph. Each represents the size of the DNA fragment.

  • The possible alleles are numbered for each loci.

    • There are 13 internationally accepted loci and have become the standards for human identification

Str example
STR Example of Jill's child named Payle.

Dna interactive
DNA Interactive of Jill's child named Payle.

The website below has a STR animation demonstration. Click on human identification, profiling and then on the third circle called Today’s DNA Profiling to see the demonstration.


Three Possible Outcomes of Jill's child named Payle.

  • Match—The DNA profile appears the same. Lab will determine the frequency.

  • Exclusion—The genotype comparison shows profile differences that can only be explained by the two samples originating from different sources.

  • Inconclusive—The data does not support a conclusion as to whether the profiles match.

Dna technologies: of Jill's child named Payle.


Mitochondrial dna
Mitochondrial DNA of Jill's child named Payle.

  • Analysis of mDNA is more:

    • rigorous

    • time consuming

    • costly than nucleic testing of DNA

  • mDNA is constructed in a circular or loop

  • 37 genes are involved in mitochondrial energy generation

  • Is used when nuclear DNA typing is not possible

FBI’s CODIS DNA Database of Jill's child named Payle.

Combined DNA Index System

  • Used for linking serial crimes and unsolved cases with repeat offenders

  • Launched October 1998

  • Links all 50 states

  • Requires >4 RFLP markers and/or 13 core STR markers