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DNA Forensics DNA Forensics Lab – background I.DNA A. Human genome contains 3 billion base pairs B. Human DNA is about 99.9% the same C. The differences.

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Presentation on theme: "DNA Forensics DNA Forensics Lab – background I.DNA A. Human genome contains 3 billion base pairs B. Human DNA is about 99.9% the same C. The differences."— Presentation transcript:

1 DNA Forensics DNA Forensics Lab – background I.DNA A. Human genome contains 3 billion base pairs B. Human DNA is about 99.9% the same C. The differences in DNA is concentrated in specific regions of DNA

2 D. Variable Number of Tandem Repeats (VNTR) 1. DNA sequences from 3 to 30 base pairs (bp) long 2. Each person has unique position and number of the VNTRs in all DNA 3. From these dif a DNA fingerprint can be made – to distinguish the difDNA fingerprint

3 E. DNA can be found where? 1. hair 2. skin 3. saliva 4. semen 5. blood (most) 6. pretty much in any cells of body

4 II. DNA Fingerprinting A. Defn – a pattern of DNA characteristics that are unique to an individual B. How a DNA fingerprint is made 1. Obtain DNA 2. Isolate the VNTR – 2 methods a. Restriction Enzymes – chemicals cut DNA around each VNTRRestriction Enzymes b. PCR – polymerase chain reaction – use primers to “find” VNTR and make many copies of them

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6 3. Put DNA into a gel a. gel has massive intertwining matrix b. DNA is negative charge – so can run electricity through gel (DNA will travel to positive) c. DNA will separate by size (VNTR) i. short pieces out first ii. Like a small snake vs large snake through a jungle d. add stain to make DNA bands appear

7 Gel electrophoresis

8 V. DNA Forensics Lab Equipment A. micropipetter 1. used to measure small volumes 2. microliter (µl) = 1.0 x10 -6 liters B. gel case – to form and store gel

9 C. comb – to make wells (holes) in gel D. electrophoresing chamber – to hold gel and run electricity through gel

10 E. Power Source – supplies energy for electricity F. Centrifuge – to spin microtubes really fast to move all sample to bottom of tube  must be safe – balanced!

11 III. Restriction Enzymes (RE)RE A. Like chemical scissors to cut DNA B. Each RE cuts at specific site 1. there are at least 100 RE 2. ie:could cut after base sequence GCATT

12 Reading a DNA Fingerprint A. The fingerprint is all the bands together B. recall: shortest pieces are away from gel C. you can match evidence to suspect

13 Sample match DNA: Which lanes match?

14 D. Paternity cases are dif – Match dna bands from kid with mom – Left over on kids must be from dad – so match up

15 Sample paternity: ma kid pa 1 pa 2

16 Bellringer 4/25/11 1. What is a VNTR? Why are they important in DNA fingerprinting? 2. What are restriction enzymes? 3. Do you put wells on negative or positive side of electrophoresing chamber, why? 4. What does a centrifuge do?

17 IV. PCR – Polymerase Chain Reaction PCR A. Method to make many copies of small pieces of DNA – from small amount of DNA B. Use primers to find VNTR OR STRs- Short Tandem Repeats C. The VNTRs are then copied many times D. idea: heat, cool, heat, cool – at least 20 xidea:

18 E. PCR Mixture 1. primers – to find VNTRs – start replication 2. DNA polymerase (taq) – enzyme to add nucleotides (replicate) 3. buffer – solution 4. nucleotides – to build more DNA

19 F. Steps of PCR 1. Denature - heat DNA – to split apart 2. Hybridization or Annealing a. cool DNA b. DNA primers and polymerase attach to DNA - primers read from 5’ to 3’ end of DNA 3. DNA synthesis or Extension a. still cool b. make copy of short piece of DNA - using DNA polymerase 4. repeat cycle – heat/cool

20 PCR

21 VIDEOS DNA forensics – United Streaming – 3: E995C5A92&blnFromSearch=1&productcode=US# PCR Electrophoresis – good activity


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