DNA fingerprinting

(DNA 指紋圖譜 )

By Yu Zhi Heng

7B (30)

Historical background DNA fingerprinting was developed in 1984 by Alec. J. Jeffrey at the University of Leic

ester 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

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 repe

ats these repeat regions are usually bounded by specific

restriction enzyme sites cut out the segment of the chromosome containing t

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

peat.

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 se

veral 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 be

en 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, hemo

philia, 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 wh

o 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 us

e 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 ge

netic 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?

END