How is DNA used to solve crimes? Evidence How is DNA used to solve crimes?

What is DNA? What makes up DNA? DNA stands for deoxyribonucleic acid and contains genetic information. It is found on chromosomes located in the nucleus of our cells. DNA Image: http://science.howstuffworks.com/genetic-science/dna-evidence.htm What makes up DNA? The sides or backbone of the DNA molecule are made up of sugar (deoxyribose) and phosphate molecules. The rungs that form the middle of the molecule are made up of pairs of nucleotides or nitrogen bases. Adenine (A) pairs with thymine (T), while guanine (G) always pairs with cytosine (C). The order of the bases determines the genetic code. Double Helix Backbone Cytosine Thymine Adenine Guanine Nitrogen Bonds

How is DNA used as evidence? Each person’s DNA is different from other people (except identical twins). DNA collected from a crime scene can either link a suspect to the evidence or eliminate a suspect, similar to the use of fingerprints. DNA can identify a victim through DNA from relatives, even when no body can be found. DNA can link crime scenes together by linking the same perpetrator to different scenes locally, statewide, and across the nation. DNA can place an individual at a crime scene, in a home, or in a room where the suspect claimed not to have been. DNA can refute a claim of self-defense and put a weapon in the suspect's hand. It can change a story from an alibi to one of consent. DNA Strand Image & information : http://www.dna.gov/audiences/investigators/know/

What factors affect DNA evidence? Environmental factors (e.g., heat, sunlight, moisture, bacteria, and mold). Therefore, not all DNA evidence will result in a usable DNA profile. Further, DNA testing cannot identify when the suspect was at the crime scene or for how long.   CODIS stands for COmbined DNA Index System, which is an electronic database of DNA profiles that can identify suspects. DNA profiles from individuals convicted of certain crimes, such as rape, murder, and child abuse, are entered into CODIS and help officers identify possible suspects when no prior suspect existed. What is CODIS? Did you know? Each human cell contains three billion DNA base pairs. Our unique DNA amounts to 0.1% or 3 million base pairs. DNA information : http://www.dna.gov/audiences/investigators/know/

Which three statements below are true? True or False? Which three statements below are true? 1. The DNA in a man's blood is the same as the DNA in his skin cells and saliva.   2. Each person's DNA is different from every other individual's. 3. DNA can be found in all the cells in our bodies except the blood cells. 4. DNA can have forensic value even if it is decades old. 5. DNA evidence was first used to get a conviction in a trial in 1987. Watch the video segment from NOVA: "The Killer's Trail" and be ready to answer the questions on the next slide.

Choose the best answer for each. Video Quiz Choose the best answer for each. 1. Who was the victim? A. Marilyn Sheppard B. Sam Sheppard C. Sam Sheppard, Jr. 2. What are the keys to DNA fingerprinting? Chromosomes B. Alleles C. Nitrogen bases 3. Where did the scientist get the sample of DNA for Marilyn Sheppard? A. Hair B. Skin C. Fingernail 4. Whose blood was found in the blood trail? A. Marilyn Sheppard B. Sam Sheppard C. Neither

DNA Fingerprints: Gel Electrophoresis DNA fingerprints identify people at the molecular level.

Sex, Lies and DNA https://www.youtube.com/watch?v=BRtgNOD0I_w

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.

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

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

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 if the DNA found at the crime scene belongs to the suspect

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

Make a DNA fingerprint (restriction map) based on the DNA sequence repeats below

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

DNA fingerprinting is used for identification. DNA fingerprinting depends on the probability of a match. Many people have the same number of repeats in a certain region of DNA. The probability that two people share identical numbers of repeats in several locations is very very small. (mother) (child 1) (child 2) (father)

Children share some bands with both parents

DNA Fingerprinting Video 2m25s

Several regions of DNA are used to make DNA fingerprints. Individual probabilities are multiplied to find the overall probability of two DNA fingerprints randomly matching. 1 1 1 1 500 90 120 5,400,000 1 chance in 5.4 million people to have the same DNA fingerprint x = 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.

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

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

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!!

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.

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.

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