dna evidence how can dna be used to solve crimes?

DNA Evidence

How can DNA be used to solve Crimes?

Do Now: Why is DNA considered circumstantial evidence?

In groups of 5 or less, work together on the DNA questions. Write all names and answers on loose-leaf paper. Hand in.

Closure: At a crime scene, list at least 3 places investigators should look for DNA evidence.

Objective: Describe how DNA can be analyzed and used as evidence.

Do Now: Where can DNA come from? Brainstorm all evidence that may have DNA

Objectives: Describe what DNA is and identify the different types of DNA

What is DNA?DNA contains genetic information.

Found on chromosomes located in the nucleus of our cells**

Individual Evidence

Objectives: Describe what DNA is and identify the different types of DNA

Made up of base pairs: (think of a bar code)

A – TC – G

The order of the base pairs determines the genetic code

Objectives: Describe how DNA can be analyzed and used as evidence. Explain the importance of CODIS in forensic science.

ADENINE

THYMINECYTOSINE

GUANINE

Complimentary

Base PairingAGTACG

TCATGC

Human DNA50% of a person’s DNA comes from each parent

23 pairs (46 chromosomes) in nucleus of most cells*1 chromosome in each pair is inherited from mother and other from the father

Every person has a different DNAsequence expect identical twins.

**How can we distinguish between identical twins apart?


Types of Human DNANUCLEAR DNA: found in chromosomes

Used for DNA FingerprintingUnique to individual

MITOCHONDRIAL DNA: Found in mitochondria

Inherited from motherNot uniqueExample: bone, hair shaft

Objectives: Describe the different types of DNA can be analyzed and used as evidence.

Why use mDNA?More stable over time/conditions*

Can get more DNA if sample is limited

Can get DNA from a highly degraded source

Objectives: Describe how DNA can be analyzed and used as evidence.

How is DNA used?

Identify a victim

Link or exclude suspect to crime scene/evidence

Link multiple crime scenes

Establish Maternity/Paternity


What Factors Affect DNA evidence

Heat, sunlight, moisture, bacteria, and mold (this was a major issue in the O.J. Simpson Case)

Not all DNA evidence will result in a usable DNA profile.

DNA testing cannot identify when the suspect was at the crime scene or for how long.


What is CODIS?

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 identify possible suspects when no prior suspect existed.


Introduction to DNA Fingerprinting

http://www.youtube.com/watch?v=RLpalVirlTk#t=322





1. When did DNA start to be an important tool in forensics?A. 1880s B. 1960s C. 1980s

2. What type of evidence does the FBI consider its most powerful tool?A. Fingerprints B. Blood C. DNA

3. What program is used to match DNA samples to possible contributors?A. CODIS B. AFIS C. DNA Code

4. What is it called when the program makes a match?A. Hot Hit B. Cold Hit C. Dead Hit

5. How many criminals have been convicted based on this software?A. 300 B. 900 C. 1,500

Watch the video and then answer the questions.Video Link:

http://videos.howstuffworks.com/tlc/29325-understanding-using-genes-to-help-solve-crimes-video.htm



Do Now: What are some factors that degrade (affect) DNA?

Objectives: Describe the role of DNA in the O.J. Simpson case

1. When did DNA start to be an important tool in forensics?A. 1880s B. 1960s C. 1980s

2. What type of evidence does the FBI consider its most powerful tool?A. Fingerprints B. Blood C. DNA

3. What program is used to match DNA samples to possible contributors?A. CODIS B. AFIS C. DNA Code

4. What is it called when the program makes a match?A. Hot Hit B. Cold Hit C. Dead Hit

5. How many criminals have been convicted based on this software?A. 300 B. 900 C. 1,500

The answers are …

http://law2.umkc.edu/faculty/projects/ftrials/Simpson/Dna.htm

Complete DNA and the O.J. Simpson case study

Closure: The DNA found at the scene only shows OJ was present for the crime. What other evidence could they/did they find to try to link him as their major suspect?

Objectives: Describe the role of DNA in the O.J. Simpson case





Do Now: What is a DNA Fingerprint?

The method of identification based on an individuals DNA:

Objectives: Describe how a DNA fingerprint is performed

2 Main Types of DNA Testing

1. RFLP: * analyzes variable lengths of DNA cut by restriction enzymes.

requires large amounts of DNA and no degradation

RFLP: Restriction Fragment Length Polymorphism.


Restriction enzymes: cut DNA at specific base sequences resulting in variable lengths of DNA


Gel Electrophoresis: Method of separating molecules of DNA within an electric field based on the size and charge of DNA fragments


http://www.dnalc.org/resources/animations/gelelectrophoresis.html

More probes taken, the better the match probability will be.

Denim blue jeans actually interfere with the restriction enzymes!





How are gel electrophoresis results analyzed?


DNA and Paternity


Complete the following activities:Who are the parentsWhich man is the father

Closure: If everyone gave their DNA to CODIS every substantial crime could be run through the CODIS program to produce cold hits. This would solve more crimes faster. Would you agree to giving your DNA to the government to run a program like that?


Do Now: What does a restriction enzyme do?


2nd Main type of DNA testing:

PCR: (Polymerase Chain Reactions) specific sequences of DNA that have high variability (differences) are copied millions of times

Less DNA needed and can be partially degraded


http://www.wiley.com/college/boyer/0470003790/animations/pcr/pcr.htm

Newest type of DNA testing:

STR: Evaluates specific short repeating regions (loci) within nuclear DNA

FBI uses 13 standard specific STR regions for CODIS


G-G-C-C-X-X-X-G-G-C-C-X-X..G-G-G-C-C-X-X-G-G-C-C-X-X…..

STR

C-C-X-X-X-G-G C-C-X-X-G-G

PCR amplifySTR region

STR

well well

Gelelectrophoresis

Person A Forensic sample

For 1 STR sequence at 1 locus

Complete STR profile


STR match probabilities are 1 in a quintillion (1x1018) or more


Complete “The break in” activity and concepts of biotechnology reading. And hand in.

Closure: Name three different reasons why a DNA profile may be needed to identify a person.


Do Now: What is an advantage to PCR over RFLP?

Objectives: Construct a gel electrophoresis simulation and determine who committed the crime

Start the individual DNA Fingerprinting Lab and hand in.

Closure: If we only have 4 bases (AGCT) that our DNA is made up of, how can everyone's DNA be completely different? Hand in your closure/do now sheet.

Objectives: Construct a gel electrophoresis simulation and determine who committed the crime

Do Now: Can any two people have the same DNA? Can any have the same mDNA?

Finish the individual DNA Fingerprinting Lab and hand in.

Closure: Do other animals have DNA?

Objectives: Construct a gel electrophoresis simulation and determine who committed the

crime

Do Now: There’s a copy of our entire DNA sequence in every cell of our body with one exception: red blood cells. But our sex cells only have ______ of our DNA.

Finish the individual DNA Fingerprinting Lab and hand in. (20min)


crime

Complete the DNA profile review sheet. Hand it in.

Closure: Besides determining suspects or paternity, what else can DNA be used for?


crime

Do Now: Why does the DNA travel to the bottom of the gel electrophoresis chamber?

Watch the video and take notes on your handout. This will be due tomorrow when we finish the video.

Closure: What DNA did the suspect leave behind?


Do Now: What are the base pairs I DNA and how do they match up?

Start the group DNA profile lab and hand in.

Closure: One chromosome can have as little as 50 million base pairs or as much as 250 million base pairs. How many chromosomes do we have?


crime

Do Now: What does the gel electrophoresis do?

Complete the group DNA profile lab and hand in.

Closure: Check your grades. Write down what you are missing.


crime

dna evidence how can dna be used to solve crimes?

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