Ch. 11: DNA Analysis

DNA: Deoxyribonucleic Acid Nucleotide: Sugar (deoxyribose) Phosphate Nitrogenous Base 4 different bases: Adenine Thymine Cytosine Guanine

DNA: Deoxyribonucleic Acid Found in all nucleated body cells: WBC, saliva, semen, urine, hair root, teeth, bone, soft tissue, etc. RBC have no nuclei, therefore DNA in blood samples comes from WBC Most abundant in buccal (cheek) cells

Restriction Enzymes Bacterial defense mechanism Cut DNA molecules at specific sites (certain nucleotide sequences) We will be using Hae III

Hae III cut site . . . C C G G . . . . . . G G C C . . .

Gel Electrophoresis Uses electric current to separate DNA fragments by size Smaller DNA pieces migrate faster through gel

DNA Fingerprinting Everyone’s DNA sequence is slightly different (0.1%, or 3 million base pairs) Restriction enzymes cut different sized pieces (fragments) RFLP = restriction fragment length polymorphism

Uses of DNA Profiling To identify potential suspects To exonerate individuals To identify crime and casualty victims To establish paternity To match organ donors

DNA Exoneration

DNA evidence makes up part of the case against the defendant

Polymerase Chain Reaction (PCR) Uses DNA polymerase to amplify DNA (make a LOT of copies of a target sequence) Valuable when amount of evidence is minimal Millions of copies can be made from a single speck of blood

Short Tandem Repeats (STR) STR’s are locations (loci) on the chromosome that contain short sequences of 2 to 5 bases that repeat themselves in the DNA molecule. The advantages of this method are that it: Offers greater specificity* Requires less time Requires smaller sample size Is less susceptible to DNA degradation *The number of possible individual STR profiles greatly exceeds the estimated number of humans who have ever lived, so it is nearly impossible for a random match to occur.

FBI’s CODIS DNA Database Combined DNA Index System Used for linking serial crimes and unsolved cases with repeat offenders Launched October 1998 Links all 50 states Requires 4+ RFLP markers and/or 13 core STR markers

CODIS = Combined DNA Index System

STR Genetic Profile Allelic Ladders D3S1358 VWA FGA AMEL D8S1179 D21S11 D18S51 D5S818 D13S317 D7S820

STR Example Profile

STR Interactive Animation The website below has an informative STR animation demonstration. Click on “human identification”, “profiling” and then on the third circle called “Today’s DNA Profiling” to see the demonstration. http://www.dnai.org/d/index.html Print & complete the STR WORKSHEET before your next NB check!

Mitochondrial DNA (mtDNA) Found in cytoplasm of cells Inherited only from the mother (egg cell) mtDNA is constructed in a circular or loop As opposed to nuclear DNA, analysis of mtDNA is more: rigorous time consuming Costly Is used when nuclear DNA typing is not possible (i.e. skeletal remains)