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DNA Analysis Chapter 11 Learning Objectives • Know the structure and function of DNA. • Understand how DNA is applied in forensic science. • Extract DNA from cells. • Apply the concepts of RFLP, PCR, and STRs to characterizing DNA. • Comparing DNA fingerprints. Biology of DNA • Cell – the smallest unit of life. Biology of DNA • Nucleus – the control center of the cell. Biology of DNA • Chromosomes – long, threadlike groups of genes found in the nucleus. Biology of DNA • DNA (deoxyribonucleic acid) – hereditary material of most organisms. Biology of DNA • Gene – a specific sequence of nucleotides in the DNA that codes to make specific proteins. Function of DNA • Sections of DNA, called genes, code for specific proteins. • Proteins then determine human traits. Structure of DNA • DNA – a long-chain molecule made of four bases that are paired and held together with hydrogen bonds and a sugar-phosphate backbone. Nitrogen Bases • • • • Adenine Thymine Guanine Cytosine Complimentary Base Pairs • Adenine and thymine are connected with two hydrogen bonds. • Cytosine and guanine are connected with three hydrogen bonds. Backbone of DNA • Deoxyribose – sugar in DNA • Phosphate groups Nucleotides • Nucleotide units = base + sugar + phosphate • Outside – sugar and phosphate • Inside – base pair & hydrogen bonds Forensic Uses of DNA • Identify a potential suspect whose DNA may match crime scene evidence • Clear the wrongly accused • Identify victims • Establish paternity • Match organ donors with recipients Samples from Crime Scenes • Determine if useful • Specimen removed from object (clothing, skin, weapon) • DNA is extracted from cellular components • Enzymes release DNA from chromosomes. • DNA is ready for characterization. RFLP Analysis • Restriction Fragment Length Polymorphism • Restriction enzymes – recognize a specific sequence of bases and cut the DNA molecule at a specific point • Probe – a portion of DNA with a known sequence of bases that is used to find its complimentary strand. Statistical Analysis in DNA Fingerprinting • What are the chances of two people having the same size fragment? • Remember, we are not looking at the sequence…only size. PCR and DNA Fingerprinting • Polymerase Chain Reaction – lab technique used to make multiple copies of DNA for further testing. • Separation • Adding Primer • Synthesis of New Chain STR: Short Tandem Repeats • STRs – specific sequences of DNA fragments that are repeated at a particular site on a chromosome. • VNTR – variable number of tandem repeats. • Scientists scan 13 regions of VNTRs. Example VNTR Mitochondrial DNA • Mitochondria – power houses of the cell. • Mitochondrial DNA comes from the mother. • Analysis takes much longer and is much more expensive.