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DNA Analysis Forensics Chapter 11.

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Presentation on theme: "DNA Analysis Forensics Chapter 11."— Presentation transcript:

1 DNA Analysis Forensics Chapter 11

2 DNA DNA “fingerprinting” is a common way to identify people by their unique genetic code It is currently being used to identify the perpetrator in a crime, to identify fathers in paternity cases, and to identify unknown remains in mass disasters and other situations DNA is in every nucleated cell of the human body and can be extracted from blood, semen, urine, bone, hair follicles, and saliva.

3 Biological Aspects of DNA
A basic functional and structural element of all living things is the cell Cell functions on its own, as in a red blood cell, or in groups, as in tissues or organs Chromosomes that are inherited from both parents, are long-chain DNA molecules that are tightly bound in a specific structure Human body has approx. 35,000 genes, which are simply portions of the DNA the code the information required to make specific proteins These proteins determine human traits and functions Genes have a specific code for a specific body function, are the fundamental unit of heredity, and determine traits of organisms

4 Biological Aspects of DNA
DNA= deoxyribonucleic acid and is a long-chain molecule made of four nitrogenous bases that are paired and held together with hydrogen bonds and a sugar-phosphate backbone Adenine pairs with Thymine; Cytosine pairs with Guanine Structure determines function Ability to replicate itself Structure= double helix

5 Biological Aspects of DNA
Average DNA molecule contains approx. 100 million nucleotide groups In humans, the order of these nucleotide bases is 99.9% the same The unique sequence of the other 0.1% makes each human one of a kind (except in identical twins, who have the same DNA) The sequence of these bases is a code for specific amino acids to combine to make specific proteins The sequence of the nucleotide bases is what determines the proteins that will lead to specific growth, functions, and reproduction

6 Forensic Uses of DNA Blood and bodily fluids are the most common evidence that forensic scientists use for testing DNA Blood is made up of RBCs that carry oxygen throughout the body; plasma, the fluid that carries the cells; platelets, which facilitate clotting; and WBCs, which defend the body against infection RBCs do not contain nuclei (means no DNA) WBCs contain nuclei (scientists want this!!) Polymerase Chain Reaction (PCR) is used to make copies so DNA can be tested

7 Forensic Uses of DNA DNA fingerprinting can be useful for many purposes: To identify potential suspects whose DNA may match evidence left at crime scenes To clear persons wrongly accused of crimes To identify crime and catastrophe victims To establish paternity and other family relationship To match organ donors with recipients in transplant programs

8 Forensic Uses of DNA Samples collected from a crime scene are examined to determine whether the sample is appropriate for DNA analysis…therefore, it must be properly prepared 1. removed from object 2. extracted from the cell (DNA must be isolated- no fats, proteins, or carbohydrates) 3. enzymes used to release DNA from chromosomal packaging..then it’s ready! 

9 RFLP Analysis for DNA Fingerprinting
RFLP- restriction, fragments, lengths, polymorphism DNA is cut into smaller pieces using restriction enzymes then the sample is run through electrophoresis, which separates the fragments according to size. Four main procedures in DNA fingerprinting Isolation of the DNA to separate the DNA from the cell Cutting with a restriction enzyme to make shorter base strands Sorting the segments by size, using an electrophoresis procedure Analyzing the resulting print by identifying specific alleles

10 Statistical Analysis in DNA Fingerprinting
The DNA molecule is hundreds of thousands of base pairs long Think: what are the chances of someone else having the same size fragment? We don’t care if the sequence is the same, only that the fragments are the same length.

11 PCR and DNA Fingerprinting
When there is little evidence to work with, PCR is used because it can make many copies in a short period of time Steps in PCR Separation Adding primer (begins replication process) Synthesis of new chain

12 STR: Short Tandem Repeats
Example: GATAG ATAGATAGAT AGATAGATAG Found on every chromosome and can easily be amplified Benefits to DNA analysis Takes less time Smaller sample size Exclusionary…eliminates more people faster! Allows for cross jurisdiction verification

13 Mitochondrial DNA Another structure in the cell that contains DNA is the mitochondria Mitochondria are the powerhouses of the cell Each cell contains thousands of mitochondria, each containing several loops of DNA mDNA is inherited from only the mother This makes any individual with the same maternal lineage indistinguishable if mDNA is used for analysis Techniques scientists use to characterize mitochondrial DNA are significantly more sensitive than the techniques for profiling nuclear DNA…but it’s more expensive FBI has only a few labs that will do mDNA testing and there are VERY strict limitations to the cases they will accept.

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