DNA fingerprinting

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Information about the DNA finger Printing

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DNA fingerprinting DNA profiling (also called DNA testing, DNA typing, or genetic fingerprinting) is a technique employed by forensic scientists to assist in the identification of individuals by their respective DNA profiles

DNA PROFILING:

2 DNA PROFILING 1980 - American researchers discovered non-coding regions of DNA 1984 - Professor Alec Jeffreys developed the process of DNA profiling 1987 - First conviction based on DNA evidence

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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

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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

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

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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.

STAGES INVOLVED:

7 STAGES INVOLVED Cells broken down to release DNA DNA strands cut into fragments Fragments separated Pattern of fragments analysed

1. DNA EXTRACTION:

8 1. DNA EXTRACTION

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9 2. DNA CUTTING 3. FRAGMENT SEPARATION The samples containing the fragments are pipetted into individual wells in a gel

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An EcoR1 restriction enzyme

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RFLP Analysis: RF stands for Restriction Fragments . Those are the fragments that were cut by restriction enzymes. L stands for Length , and refers to the length of the restriction fragment. P stands for Polymorphisms , a Greek term for “many shapes”. The lengths of some of the restriction fragments differ greatly between individuals. RFLP = Restriction Fragment Length Polymorphism

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Molecular biologists have identified regions of the human genome where restriction fragment lengths are highly variable between individuals. Electrophoresis of these RFLP’s produce different patterns of DNA bands. With 3 billion base pairs in the human genome, however, RFLP analysis would produce a ‘smear’ of many similar sized fragments.

ELECTROPHORESIS:

13 ELECTROPHORESIS Fragments separated by length DNA (negatively charged) Moves towards +ve terminal Shorter fragments move faster

4.DNA TRANSFER:

14 4.DNA TRANSFER DNA split into single strands using alkaline solution DNA fragments transferred from gel to filter paper or nylon membrane (This is called Southern blotting) Gel, with filter paper attached, is removed & separated

5. ANALYSIS:

15 5. ANALYSIS Radioactive probe in solution binds to DNA Revealing a pattern of bands X-ray film

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16 HOW DNA PROBES WORK

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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.

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Red boxes represent the repeat unit and the blue lollipops represent cut sites for a restriction endonuclease. (Here 3 different variants, may be 50 in reality).

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Analysis of a VNTR locus most commonly results in a two-band pattern, one band inherited from each parent. A one-band pattern can occur if the size of the two parental bands are the same or nearly the same. For our simple example of three different alleles designated A, B, and C illustrated above, six unique DNA profiles are possible.

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The possible genotypes are AA, BB, CC, AB, BC, and AC

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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

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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.

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4-6: DNA fingerprint. The final DNA fingerprint is built by using several probes (5-10 or more) simultaneously.

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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?

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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

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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.

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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

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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.

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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

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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

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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?

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The Federal Bureau of Investigation (FBI) has been a leader in developing DNA typing technology for use in the identification of perpetrators of violent crime. In 1997, the FBI announced the selection of 13 STR (short tandem repeat) loci to constitute the core of the United States national database, CODIS. All CODIS STRs are tetrameric repeat sequences. All forensic laboratories that use the CODIS system can contribute to a national database.

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For example, D7S280 is one of the 13 core CODIS STR genetic loci. This DNA is found on human chromosome 7. The tetrameric repeat sequence of D7S280 is "gata". Different alleles of this locus have from 6 to 15 tandem repeats of the " gata " sequence.

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