Application of Biotechnology in DNA Fingerprinting and Forensic Analysis. Copyright 2009 Pearson Education, Inc.

Transcription

1 Application of Biotechnology in DNA Fingerprinting and Forensic Analysis

2 Introduction to DNA Fingerprinting and Forensics Forensic science intersection of law and science Historic examples Early 1900s fingerprints DNA Fingerprinting 1985 Unique signature found in each person s genetic

3 What Is a DNA Fingerprint? DNA fingerprints is a way of identifying a specific individual,. It is also known as genetic fingerprinting or DNA profiling. Uses: identifying paternity or maternity and for identifying criminals or victims Every individual carries a unique set of genes Chemical structure of DNA is same, but the order of the base pairs differs Every cell contains a complete set of DNA that identifies the organism as a whole Only one tenth of 1% of DNA differs from person to person

4 Fingerprinting DNA fingerprinting uses a specific type of DNA sequence, known as a microsatellite, to make identification Microsatellites are short pieces of DNA (1-6 base) which repeat many times (1-100 times) in a given person's DNA. In a given area, microsatellites tend to be highly variable, making them ideal for DNA fingerprinting. By comparing a number of microsatellites in a given area, one can identify a person relatively easily. Also called short tandem repeats (STR) FBI has chosen 13 unique STRs for testing Combined DNA Index System (CODIS)

5 Paternity/maternity verification The sections of DNA used in DNA fingerprinting, although highly variable, are passed down from parents to their children no child has pairs that their parents do not have

6 Forensic forensics is considered a very critical part of any investigation Witnesses can often be mistaken, have fading memories, or even pass away, forensics "tells the same story" no matter how many times it is tested, or how many years have passed. DNA fingerprinting is very attractive because it doesn't require actual fingerprints All the DNA sections are contained in every cell, any piece of a person's body, from a strand of hair to a drop of blood, may be used to identify them using DNA fingerprinting

7 Two Main Types of Forensic DNA Testing RFLP (restriction fragment length polymorphism) Requires larger amounts of DNA DNA cannot be degraded PCR (polymerase chain reaction) Less DNA and DNA can be partially degraded Extremely sensitive to contaminating DNA

8 What Is a DNA Fingerprint? DNA profiling depends on a small portion of the genome Exons code proteins Introns do not code for proteins DNA fingerprint use the introns for identification the individu

9 Prokaryotes vs eukaryotes The introns contain repeated sequences of between 1 and 100 base pairs Called variable number tandem repeats (VNTR s) Some VNTR s are inherited from mother and some from father

10 What Is a DNA Fingerprint?

11 Preparing a DNA Fingerprint DNA Collection Search for sources of DNA Collection requires attention : Wear disposable gloves; change them frequently Use disposable instruments Avoid talking, sneezing, and coughing Avoid touching any item that might contain DNA(face, nose, or mouth)

12 Preparing a DNA Fingerprint Enemies of Evidence Sunlight and high temperature Bacteria Moisture DNA fingerprinting is a comparative process Samples from crime scene must be compared to suspect DNA Best sample from suspect DNA is fresh, whole blood

13 RFLP A molecular method of genetic analysis that allows individuals to be identified based on unique patterns of restriction enzyme cutting in specific regions of DNA The technique takes advantage of the polymorphisms in individual pe ople's genetic codes. Polymorphism: multiple forms of a single gene that can exist in an individual or among a group of individuals.

14 Preparing a DNA Fingerprint RFLP (restriction fragment length polymorphism) Analysis cutting a particular region of DNA with known variability, with restriction enzymes, Separating the DNA fragments by agarose gel electrophoresis and determining the number of fragments and relative sizes. The pattern of fragment sizes will differ for each individual tested. RFLP focuses on segments that contain sequences of repeated DNA bases, which vary widely from person to person.

15 Preparing a DNA Fingerprint Southern Blot Technique Transfer DNA fragments from gel to nitrocellulose or nylon membrane Membrane incubated with a probe Short strand of complementary DNA with a radioactive or fluorescent tag Targeted area on the DNA fragment is called a locus Expose X-ray (photo) film to membrane to obtain permanent record of results

16 Preparing a DNA Fingerprint

17 Preparing a DNA Fingerprint PCR used to amplify DNA found at crime scene into an amount that can be analyzed DNA produced is identical to the original sample Use PRIMER to identify the suspect