DNA PROFILING DNA FINGERPRINTING

DNA TYPING

(CHAPTER 7)

human to human genetic 99.5% identical or .5% different

There are 50 – 75 TRILLION CELLS IN A HUMAN BODY

Perspective on 50 trillion

Perspective on 50 trillion

Perspective on 50 trillion

The facts:

Each person is made of cells Each cell has DNA unique to that

individual (excluding identical twins) Each cell is 99.5 % similar to any

other person on earth. 0.5% difference exists !

This small difference is what is analyzed in order to differentiate between people.

Non-coding DNA = DNA that doesn’t do anything noticeable

3 non-coding regions useful to f.s.

1. SNP = SINGLE NUCLEOTIDE POLYMORPHISM

2. STR = SHORT TANDEM REPEATS

3. VNTR = VARIABLE NUMBER of TANDEM REPEATS

Single Nucleotide Polymorphism’s (SNP’s)

http://www.youtube.com/watch?v=5raJePXu0OQ

1.

Short Tandem Repeats (STR’s) (2-5 base pairs in length)

2.

Variable Number of Tandem Repeats (VNTR) (9-80 bases in length)3.

BECAUSE WE KNOW THESE DIFFERENCEZ BETWEEN PEOPLE EXIST, WE CAN CREATE A TECHNIQUE TO EXPLOIT THESE DIFFERENCES

THE TECHNIQUE:

DNA profiling = comparing one individual’s DNA with another.Uses a technique called gel electrophoresis

Gel Electrophoresis

http://www.youtube.com/watch?v=PSwlCk_Z02c

PROBLEM WITH ELECTROPHORESIS

The problem: The test requires more DNA than is typically found at a crime scene.

The solution is…..

POLYMERASE CHAIN REACTION (PCR)

PCR = Increasing the available DNA until there is enough to perform DNA profiling.

How it works: learn.genetics.utah.edu/content/labs/pcr/

= online lab we can watch

It’s too little DNA

Collect evidence

Extract DNA

It’s enough DNA

“Run” Electrophoresis

Amplify DNA (P.C.R.)

Compare results

Restrict DNA (chop it up)

Restrict DNA (chop it up)

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How does one cut DNA

TINY SCISSORS

Restriction enzyme

Restriction enzymes = cut DNA at EXACT locations

NOTE: There are over 6,000 known R. E.’s and therefore 6,000 different options of where to cut .

SO HERE’S THE QUESTION: If we want a specific piece of DNA how can we remove it from the loooooong strand of DNA?

Important part(NON-CODING REGION)

PROBLEM: THIS IMPORTANT PART OF DNA ISN’T ENOUGH TO WORK WITH… IF ONLY WE COULD AMPLIFY THE DNA

Thermocycler = PCR machine (amplifies DNA)

SOLUTION….

PCR THIS IMPORTANT PIECE

(Make a billion copies!)

Gel Electrophoresis

http://www.youtube.com/watch?v=PSwlCk_Z02c

NOW WE PUT THESE PIECES INTO GEL ELECTROPHORESIS

START’S HERE

MOVES DOWN HERE

A home invasion At point of entry, a

broken shard of glass cut the criminal leaving blood “A”.

At the hospital were 4 people who fit the profile AND had cuts that could have been made at the crime scene.

HOW IT CAN SOLVE CRIMES

IMPORTANT !

If the profile matches the suspect it provides strong evidence that the suspect was present at the crime scene (doesn’t prove they committed the crime)

If the profile doesn’t match the suspect then that suspect may be eliminated from the enquiry.

Comparisons can tell us:

Paternity (relatedness) Medical Problems

DNA profiling can tell:

Medical Issues Paternity suits

Legal issues Inheritance cases Immigration cases

1. Paternity and Maternity Because a person inherits his or her VNTRs from his or her parents, VNTR patterns can be used to establish paternity and maternity. The patterns are so specific that a parental VNTR pattern can be reconstructed even if only

the children's VNTR patterns are known the more children produced, the more reliable the reconstruction).

Parent-child VNTR pattern analysis has been used to solve standard father-identification cases as well as more complicated cases of confirming: legal nationality biological parenthood.

2. Criminal Identification and Forensics DNA isolated from blood, hair, skin cells, or other genetic evidence left at the scene of a crime can be compared, through VNTR patterns, with the DNA of a criminal suspect to determine guilt or innocence. VNTR patterns are also useful in establishing the identity of a homicide victim, either from DNA found as evidence or from the body itself.

3. Personal Identification The notion of using DNA fingerprints as a sort of genetic bar code to identify individuals has been discussed, but this is not likely to happen anytime in the foreseeable future. The technology required to isolate, keep on file, and then analyze millions of very specified VNTR patterns is both expensive and impractical. Social security numbers, picture ID, and other more mundane methods are much more likely to remain the prevalent ways to establish personal identification.

Biological material used for DNA profiling

Blood Hair Saliva Body tissue cells DNA samples have been obtained from

vaginal cells transferred to the outside of a condom during sexual intercourse.

Famous cases

2002 Elizabeth Hurley used DNA profiling to prove that Steve Bing was the father of her child Damien

Famous Cases

Colin Pitchfork was the first criminal caught based on DNA fingerprint evidence.

He was arrested in 1986 for the rape and murder of two girls and was sentenced in 1988.

Famous Cases

O.J. Simpson was cleared of a double murder charged in 1994 which relied heavily on DNA evidence.

This case highlighted lab difficulties.

Who invented DNA Profiling?

Sir Alec Jeffreys at the University of Leicester, UK in 1985.

He was knighted in 1994!

THE END

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Stages of DNA Profiling

Stage 1: Cells are broken down to release DNA If only a small amount of DNA is

available it can be amplified using the polymerase chain reaction (PCR)

Stages of DNA Profiling

Step 2: The DNA is cut

into fragments using restriction enzymes.

Each restriction enzyme cuts DNA at a specific base sequence.

Stages of DNA Profiling

The sections of DNA that are cut out are called restriction fragments.

This yields thousands of restriction fragments of all different sizes because the base sequences being cut may be far apart (long fragment) or close together (short fragment).

Stages of DNA Profiling

Stage 3: Fragments are separated on the basis of

size using gel electrophoresis. DNA fragments are injected into wells

and an electric current is applied along the gel.

Stages of DNA Profiling

DNA is negatively charged so it is attracted to the positive end of the gel.

The shorter DNA fragments move faster than the longer fragments.

DNA is separated on basis of size.

Stages of DNA Profiling

A radioactive material is added which combines with the DNA fragments to produce a fluorescent image.

A photographic copy of the DNA bands is obtained

Stages of DNA Profiling

Stage 4: The pattern of fragment distribution is

then analyzed.

Uses of DNA Profiling

DNA profiling is used to solve crimes and identify relatedness (who da baby daddy)