The Case of the Druid Dracula: Clicker Case Version

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The Case of the Druid Dracula: Clicker Case Version

Adapted from Brickman (2004). The Case of the Druid Dracula. National Center for Case Study Teaching in Science, University at Buffalo, State University of New York.

by Norris Armstrong, Terry Platt, and Peggy Brickman

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CQ1: What is your blood type?

A: AB: BC: ABD: OE: Don’t know

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Evidence in the Courtroom

• Primarily rape cases• Paternity testing• Historical/missing persons investigations• Military “dog tag”• Convicted felon databases

• Blood was previously used for blood typing• Now it is used as a source of DNA

Which cells in the blood contain DNA?

Uses for DNA fingerprinting

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The Crime

In a quiet corner of Wales in the village of Llanfairpwll, 90-year-old Mabel Leyshorn was murdered. Her murder had been not only brutal (her heart had been hacked out), but also creepy. It appeared as if Mabel’s blood had been collected in a small kitchen saucepan and tasted. The murder showed other signs of the occult: a candlestick and a pair of crossed pokers had been arranged near the body.

- from BBC’s Crimewatch December 2001

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The Crime SceneFurther investigation indicated that this was no supernatural villain at work: the murderer had worn tennis shoes which had left distinctive footprints under the glass door that had been shattered by a piece of broken garden slate. Moreover, the windowsill had bloodstains on it; with any luck, the evidence recovery unit hoped to use it to help determine who had committed the crime.

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•Antiparallel

•Complementary

DNA Structure- Review

Two DNA chains

?′ end

3′ end 5′ end

3′ end

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Copying DNA (Replication)

ATCGGACT

TAGCCTGA

--------

DNA strands are separated

Each single strand is used as a template to make a complementary strand

Two identical DNA molecules are produced

ATCGGACT

TAGCCTGA

- GA-T-

T -C -A -

ATCGGACT

--------

TAGCCTGA

--------

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Enzymes Perform Replication• Helicases unwind DNA double helix.• Single Stranded Binding Proteins hold separated

DNA strands apart.• Primase makes a starting point (primer).• DNA polymerase connects new complementary

bases.• Ligase attaches pieces together.

CQ2: Which enzyme elongates the new DNA daughter strand?A.DNA polymerase IB.DNA Polymerase III

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Enzymes Perform Replication

Replication fork

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DNA in the CellDNA in the Cell

Target GeneTarget Gene

chromosome

double stranded DNA molecule

individual nucleotides

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Example: Amelogenin Gene • Target sequence to be copied in this gene is located in Intron 1• Gene function: tooth enamel development • Copies on both X and Y chromosome• X copy is different from Y copy

X copy is shorter than Y copy

Y:

X:

--- indicates missing bases on X

5’CCCTAGGGTCTA---------GTGTGTTGATTC 5’3’GGGATCCCAGAT---------CACACAACTAAG 3’

GTGTGTTGATTC 3’CACACAACTAAG 5’

5’CCCTAGGGTCTATAACGCCTAGTGTGTTGATTC 5’3’GGGATCCCAGATATTGCGGATCACACAACTAAG 3’

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CQ3: Below is one strand from part of the amelogenin gene. What is the nucleotide sequence of the complementary strand?

A: 3′ -ACTGTTAGATT-5′ B: 3′ -GGGACCCGAGA-5′ C: 5′ -GGGACCCGAGA-3′ D: 3′ -CCCTGGGCTCT-5′ E: 5′ -CCCTGGGCTCT-3′

5’-CCCTGGGCTCT-3’

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CQ4: How would DNA replication be affected if ligase were not available?

A: The template strands would not be able to separate.

B: Replication would result in many small segments of DNA instead of a complete molecule.

C: Complementary RNA would be produced but not complementary DNA.

D: The DNA strands would separate but replication would not be able to start.

E: The DNA strands produced by replication would not be complementary to the template strands.

14In 32 cycles at 100% efficiency, 1.07 billion copies of targeted DNA region are created

In 32 cycles at 100% efficiency, 1.07 billion copies of targeted DNA region are created

Amplifying DNA with PCR (Polymerase Chain Reaction)Amplifying DNA with PCR (Polymerase Chain Reaction)

Target region

Thermal cycleThermal cycleThermal cycle

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CQ5: In order to conduct forensic tests, you need many copies of the amelogenin gene target sequence, which you will make using Polymerase Chain Reaction (PCR). PCR follows the steps of replication. Which of the following would allow replication to begin?

A: Add short stretches of single stranded DNA complementary to the sequence at either end of the gene.

B: Add DNA polymerase enzyme.

C: Break the covalent bonds that hold the double helix together.

D: Break the hydrogen bonds that hold the double helix together. (denature)

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CQ6: Which of the strands of DNA could act as one of the two primers for the DNA sequence shown below?

5’-CCCTGGGCTCTGTAAATGTTTCTAAGTG-3’3’-GGGACCCGAGACATTTACAAAGATTCAC-5’

A: 3′ -ACTGTTAGA-5′

B: 3′ -AAATTTGGC-5′

C: 3′ -ATGCTTTGA-5′

D: 5′ -GGGACCCGA-3′

E: 5′ -CCCTGGGCT-3′

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CQ7: If both of these were run through gel electrophoresis, which segment would go farther through the gel?A.YB.X

Y:

X: 5’CCCTAGGGTCTA---------GTGTGTTGATTC 5’3’GGGATCCCAGAT---------CACACAACTAAG 3’

GTGTGTTGATTC 3’CACACAACTAAG 5’

5’CCCTAGGGTCTATAACGCCTAGTGTGTTGATTC 5’3’GGGATCCCAGATATTGCGGATCACACAACTAAG 3’

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Gel Electrophoresis: Sizing DNA Fragments

(-) Negative electrode

(+) Positive electrode

#bp?

#bp?

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CQ8: The DNA fragment indicated is approximately ____ base pairs in size.

bp?

A: 300B: 350C: 580D: 600E: 700

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Why do the two DNA fragments indicated differ in how bright they appear?

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Additional Markers

---TCAT------TCAT---

Short Tandem Repeats (STRs)Short Tandem Repeats (STRs)

•Same pair in suspect 2:

•Different people have different numbers of repeats on their chromosomes

•Chromosomes 11 of suspect 1:

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Positions of other STR

regions

CSF1PO

TH01

TPOX

AMEL

Each person is unique

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Druid Dracula: DNA testing

• With kits, just add DNA sample with primers for amelogenin (XY) & different STR regions.

• Amplify and run on gel (electrophoresis).• An allele ladder shows all varieties in a population.

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Automated gels

MW Amelog.

101 bp110 bp

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CQ9: The blood left at the crime scene was from a male. Which of the following DNA profiles could have come from the suspect?

A:

B:

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CQ10: Is this enough to convict a suspect?

A: Yes

B: No

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CQ11: Which suspect presents a profile compatible to the sample found at the crime scene?A.Suspect 1B.Suspect 2

What are the Odds?• There are only a few different numbers of repeats that

are seen in our population.– Ex: only 5 different TPOX STRS

• After testing thousands of DNA samples, researches know the distribution of these different STRS in the general population.

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THO1 TPOX CSF1PO

5: 1/200 8: ½ 9: 1/40

6: ¼ 9: 1/8 10: 1/5

7: 1/6 10: 1/18 11: 1/3

8: 1/7 11: 1/5 12: 1/3

9: 1/6 12: 1/20 13: 1/10

9.3: 1/3 14: 1/50

10: 1/100

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CQ12: What is the probability that two people might have 5 and 7 repeats for the STR THO1 by random chance?

STR THO1 allele frequencies

5 6789

9.310

1/2001/41/61/71/61/3

1/100

A: 1/200B: 1/206C: 1/600D: 1/1200E: 1/2600

What are the Odds?CQ13: What is the probability that someone else at random would have the same pattern of THO1 5 & 7, TPOX 8 & 9, and CSF1PO 11 & 12?

A.1/1600

B.1/7200

C.1/17600

D.1/172800

E.1/1555200

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THO1 TPOX CSF1PO

5: 1/200 8: ½ 9: 1/40

6: ¼ 9: 1/8 10: 1/5

7: 1/6 10: 1/18 11: 1/3

8: 1/7 11: 1/5 12: 1/3

9: 1/6 12: 1/20 13: 1/10

9.3: 1/3 14: 1/50

10: 1/100

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Hardman’s Arrest• Standard police work identified Matthew Hardman

as a suspect. Preliminary DNA testing provided enough evidence to arrest Hardman on suspicion of murder.

• During the arrest, a knife was found in his coat pocket. Subsequent DNA testing revealed two sources of DNA on the knife, one from Hardman and one matching the victim. The possibility of a random match was one in 73 million.

• A search of Hardman’s dwelling produced magazines and evidence of accessing internet sites featuring how to become a vampire. 

• Matthew Hardman was found guilty of murder on August 2, 2002, and sentenced to life imprisonment.