Chapter 9 DNA The Indispensible Forensic Science Tool
Chapter 9: DNA The Indispensible Forensic Science Tool
If you were on the jury……. Would you have enough knowledge about DNA to understand what the prosecution and or defense was presenting in court? Would you have enough knowledge to make a good judgment about guilt or innocence based on DNA evidence? … or would it be another O. J. Simpson case? ?
A polymer is a large molecule made of many repeating smaller units called monomers.
Chromosome Nucleus When forensic evidence includes DNA evidence, specifically what did forensic technologist possibly collect at the scene? Human Body Cell DNA Gene
Sources of DNA Evidence • Can be found in all body cells • • Blood Semen Saliva, Urine Hair roots Teeth Bone Muscle Tissue • Most abundant in our buccal (cheek) cells • Blood is 99. 9% red blood cells that have no nuclei; and therefore, no nuclear DNA • DNA obtained from blood comes from white blood cells
The job of DNA …. is to direct the building of proteins.
Methods of making more copies of DNA: 1. Recombinant DNA • Uses bacteria to copy fragments of DNA • Use to make vaccines • Not useful in forensic DNA analysis…. . WHY? ? ? 2. Polymerase Chain Reaction (PCR) • Uses heat, primers, and enzymes to copy strands of DNA
Bacteria are used because they reproduce rapidly, making more of the newly inserted DNA as they do. a m e s ar s i h t de e n i c Vac “Recombine” two piece of DNA from 2 different sources
The polymerase chain reaction (PCR) is a biochemical technology used to amplify a single or a few copies of a piece of DNA. It generates millions of copies of a particular DNA sequence in just two minutes.
What is DNA Typing? • Also known as DNA Fingerprinting • Method in which DNA is converted into a series of bands that ultimately distinguishes each individual. • Only one-tenth of a single percent of DNA (about 3 million bases) differs from one person to the next. Scientists use these regions to generate a DNA profile of an individual.
Process of DNA Typing? • Method consists of three basic steps: 1. Cutting DNA into small pieces 2. Separating those small pieces 3. Completing a process that makes these small pieces visible
DNA Fingerprinting
DNA Typing: aka DNA Fingerprinting http: //www. youtube. com/watch? v=dr. C 7 r. R 7 CIBg
Each probe only recognizes a DNA sequence. Multiple probes will be added to single sample so that each of the DNA segments will be visible.
RFLP vs. STR 2 types of DNA typing: 1. Restriction Fragment Length Polymorphism (RFLP) • Uses a sequence of 15 -35 nitrogenous bases to make bands on the electrophoresis gel • Can’t use PCR because the sequence is too long • Can take up to 10 weeks to complete
RFLP vs. STR 2 types of DNA typing: 2. Short Tandem Repeats (STR) • Uses a sequence of 3 -7 nitrogenous bases to make bands on the electrophoresis gel • PCR is used with these short sequences • Can be completed within about 3 days
Short Tandem Repeats STRs Counting the number of repeats by size comparison Largest AGCT 4 Repeats AGCT 3 Repeats AGCT 2 Repeats AGCT 1 Repeat Smallest
Because the DNA can be replicated in the laboratory for a STR process, it isn’t necessary forensic technicians to collect a large sample of DNA from the actual crime scene.
Types of DNA Nuclear • found in the nucleus • constitutes 23 pair of chromosomes inherited from both parents • each cell contains only one nuclei Mitochondrial • found in the cytoplasm • is inherited only from mother • each cell contains hundreds to thousands of mitochondria • can be found in skeletal remains 21
Mitochondrial DNA • Analysis of mt. DNA is more: • difficult • time consuming • costly than nucleic testing of DNA • Only used when nuclear DNA typing is not possible 22
Vietnam unknown soldier identified using mitochondrial DNA
Present Work in DNA • CODIS--Computer Based DNA Information System • A data base of DNA profiles of individuals convicted of sex crimes and other violent crime • Innocence Project • Group of college law students work on cases where DNA may prove innocence (or guilt) • Since the late 1980’s, DNA technology has been available. People, as a result, have been reopening cases and testing the evidence for DNA. Some have been exonerated because their DNA did not match. 26
FBI’s CODIS DNA Database Combined DNA Index System Used for linking serial crimes and unsolved cases with repeat offenders w Launched October 1998 w Links all 50 states w Requires >4 RFLP markers and/or 13 core STR markers w
The Future • Greater automation of the DNA typing process • Use of SNP’s--single nucleotide polymorphism which measures a one nucleotide change or difference from one individual to another. 28
Before and After • In a paragraph, describe how the process of DNA fingerprinting prior to 1990’s was different to the techniques used since that time. • Page 317 may be useful to you • Make sure to use the terms we have covered concerning these processes. • http: //learn. genetics. utah. edu/content/labs/
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