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Forensic Science: DNA Fingerprinting Techniques

Learn about DNA fingerprinting, a molecular identification method used in criminal cases, paternity tests, and biodiversity studies. Explore gel electrophoresis and probability analysis.

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Forensic Science: DNA Fingerprinting Techniques

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  1. 9.3 DNA Fingerprinting 2.1 Atoms, Ions, and Molecules • Set up Cornell Notes on pg. 17 • Topic: 9.3 DNA Fingerprinting • Essential Question: • Describe two ways in which DNA fingerprinting is used. • Describe two ways in which DNA fingerprinting is used. KEY CONCEPT DNA fingerprints identify people at the molecular level Get out your homework: Who Ate the Cheese?

  2. KEY CONCEPT DNA fingerprints identify people at the molecular level.

  3. REVIEW from 9.1 • Gel electrophoresis is used to separate DNA fragments by size. • A DNA sample is cut with restriction enzymes. • Electrical current pulls DNA fragments through a gel.

  4. A DNA fingerprint is a type of restriction map. DNA fingerprints are based on parts of an individual’s DNA that can be used for identification. • based on noncoding regions of DNA that have repeating DNA sequences • number of repeats differs between people

  5. X X A DNA fingerprint is NOT actually a fingerprint!

  6. Blood found at crime scene • Need to determine if it is the suspect’s blood, or the victim’s blood • We can use DNA fingerprinting to find out • The DNA found at the crime scene belongs to the suspect

  7. Make a DNA fingerprint (restriction map) based on the DNA sequence repeats below (p. 16) - 7 6 5 4 3 2 1 0 + # of repeats

  8. Make a DNA fingerprint (restriction map) based on the DNA sequence repeats below (p. 16)

  9. Make your own DNA Fingerprint! Quick Online Lab • http://www.pbs.org/wgbh/nova/education/body/create-dna-fingerprint.html

  10. (mother) (child 1) (child 2) (father) DNA fingerprinting is used for identification. • DNA fingerprinting depends on the probability of a match. • Many people have thesame number ofrepeats in a certainregion of DNA. • The probability that two people share identicalnumbers of repeats inseveral locations isvery small.

  11. Children share some bands with both parents

  12. DNA Fingerprinting Video 2m25s

  13. x x 1 1 1 1 500 90 120 5,400,000 = 1 chance in 5.4 million people to have the same DNA fingerprint = • Individual probabilities are multiplied to find the overall probability of two DNA fingerprints randomly matching. 1 in every 500 people has 3 copies in location A 1 in every 90 people has 6 copies in location B 1 in every 120 people has 10 copies in location c • Several regions of DNA are used to make DNA fingerprints.

  14. DNA fingerprinting is used in several ways. • evidence in criminal cases • paternity tests (Who da’ Daddy???) • immigration requests • studying biodiversity • tracking genetically modified crops

  15. The Killer’s Trial 6m30s • Read the Article • Watch the video and answer the questions

  16. Who Killed Sally Parker?: Gel Electrophoresis • A DNA Fingerprinting Simulation

  17. Today’s Task • Today you will work with a partner to perform a lab simulation based on a scenario in which you are to identify the murderer of Ms. Sally Parker. • This activity will model the processes of gel electrophoresis and DNA fingerprinting • Let’s get started!!

  18. Procedures • Begin by reading the scenario and discussing it with your partners. Be sure you understand the problem. • Get the materials needed to complete the activity.

  19. Procedures • Following base pairing rules, please fill in the complementary strand of DNA • Examine each DNA fragment strip closely, looking for the sequence AATT. This is a restriction site, where enzymes will cut the DNA into even smaller fragments. Use a pencil to mark these sites, with a line between the inner A and the inner T (AA│TT). • Then use the scissors to cut across the fragments at those sites. Count and label the number of base pairs contained in each of the DNA fragments. • Use the chart paper provided by your teacher to make a larger version of the gel electrophoresis chamber. • Use a ruler or meter stick to make sure all of the lengths are the same.

  20. Who Killed Sally Parker? Materials Needed: • Direction Packet • Pencil • Scissors • Ruler • Chart Paper • DNA Samples (7) • Tape • Bio Book (266-267) Remember to include on your poster: • Charge (+/-) • Title • Color • Circle the suspect who killed Sally Parker REMEMBER to cut @ AATT AA TT

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