DNA fingerprinting

Historical background DNA fingerprinting was developed in 1984

by Alec. J. Jeffrey at the University of Leicester

He was studying the gene of myoglobin.

This is a picture of Alec. J. Jeffrey

What is DNA Fingerprinting? The chemical structure of everyone's DNA is the

same. The only difference between people (or any

animal) is the order of the base pairs. The information contained in DNA is determined

primarily by the sequence of letters along the zipper.

Structure of DNA

9.3 DNA Fingerprinting

KEY CONCEPT DNA fingerprints identify people at the molecular level.

9.3 DNA Fingerprinting

A DNA fingerprint is a type of restriction map.

• DNA fingerprints are based on parts of an individual’s DNA that can by used for identification.– based on noncoding regions of DNA– noncoding regions have repeating DNA sequences– number of repeats differs between people– banding pattern on a gel is a DNA fingerprint

9.3 DNA Fingerprinting

DNA fingerprinting is used for identification.

• DNA fingerprinting depends on the probability of a match.– Many people have the

same number ofrepeats in a certainregion of DNA.

– The probability that two people share identicalnumbers of repeats inseveral locations isvery small.

(mother) (child 1) (child 2) (father)

9.3 DNA Fingerprinting

– Individual probabilities are multiplied to find the overall probability of two DNA fingerprints randomly matching.

– Several regions of DNA are used to make DNA fingerprints.

1 1 1 1500 90 120 5,400,000 1 chance in 5.4 million peoplex x = =

9.3 DNA Fingerprinting

• DNA fingerprinting is used in several ways.

– evidence in criminal cases

– paternity tests– immigration requests– studying biodiversity

– tracking genetically modified crops

The different sequence segments that vary in size and composition and have no apparent function are called minisatellites

The different sequences is the same as the word "POST" has a different meaning from "STOP" or "POTS," even though they use the same letters. i

Using these sequences, every person could be identified solely by the sequence of their base pairs

there are so many millions of base pairs, the task would be very time-consuming

Instead, scientists are able to use a shorter method, because of repeating patterns in DNA.

These patterns do not, however, give an individual "fingerprint,"

they are able to determine whether two DNA samples are from the same person, related people, or non-related people.

DNA Fingerprinting using VNTR's On some human chromosomes, a short sequence of

DNA has been repeated a number of times. the repeat number may vary from one to thirty

repeats these repeat regions are usually bounded by specific

restriction enzyme sites cut out the segment of the chromosome containing

this variable number of tandem repeats (VNTR's ) identify the VNTR's for the DNA sequence of the

repeat.

Making DNA Fingerprints

DNA fingerprinting is a laboratory procedure that requires six steps:

1: Isolation of DNA.

2: Cutting, sizing, and sorting. Special enzymes called restriction enzymes

are used to cut the DNA at specific places

3: Transfer of DNA to nylon.The distribution of DNA pieces

is transferred to a nylon sheet by placing the sheet on the gel and soaking them overnight.

4-5: Probing.Adding radioactive or colored probes to the nylon sheet produces a pattern called the DNA fingerprint.

4-6: DNA fingerprint. The final DNA fingerprint is built by using

several probes (5-10 or more) simultaneously.

Practical Applications of DNA Fingerprinting 1.Paternity and Maternity : person inherits his

or her VNTRs from his or her parents

Parent-child VNTR pattern analysis has been used to solve standard father-identification cases

Can someone tell me who is my father?

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

FBI and police labs around the U.S. have begun to use DNA fingerprints to link suspects to biological evidence – blood or semen stains, hair, or items of clothing

3. Personal Identification The notion of using DNA fingerprints as a sort of

genetic bar code to identify individuals has been discussed

4.Diagnosis of Inherited Disorders diagnose inherited disorders in both prenatal and

newborn babies These disorders may include cystic fibrosis,

hemophilia, Huntington's disease, familial Alzheimer's, sickle cell anemia, thalassemia, and many others.

5.Developing Cures for Inherited Disorders By studying the DNA fingerprints of relatives

who have a history of some particular disorder identify DNA patterns associated with the disease

6.identification of Chinese medicine The Hong Kong Baptist University was able to

use DNA fingerprinting to identify the Chinese medicine—Lingzhi in 2000

Considerations when evaluating DNA evidence In the early days of the use of

genetic fingerprinting as criminal

evidence, given a match that had a

1 in 5 million probability of occurring

by chance the lawyer would argue

that this meant that in a country

of say 60 million people there were 12 people

who would also match the profile.

2. Problems with Determining Probability A. Population Genetics VNTRs, because they are results of genetic

inheritance it will vary depending on an individual's

genetic background

B. Technical Difficulties Errors in the hybridization and probing process

must also be figured into the probability Until recently, the standards for determining

DNA fingerprinting matches, and for laboratory security and accuracy which would minimize error

When evaluating a DNA match, the following questions should be asked:

-Could it be an accidental random match?

-If not, could the DNA sample have been planted?

-If not, did the accused leave the DNA sample at the exact time of the crime?

-If yes, does that mean that the accused is guilty of the crime?

A Kid’s set of apparatus for DNA fingerprinting, What does it mean?

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