Using Parker Brother’s game CLUE to learn about DNA Fingerprinting

Using Parker Brother’s game CLUE to learn about DNA Fingerprinting

Credits: This exercise was designed by Sandra Porter, Geospiza, author of "Exploring DNA Structure" and is reprinted with her permission for classroom use. Teachers, read the original article about this activity at this link.

The DNA of humans is more alike than different. However, the technique of DNA fingerprinting to identify humans one from another looks at regions of the human genome where there is great variability among human individuals. Typically these areas of the genome are not working genes and so over time, have been free to vary without selective pressures. These hypervariable parts of the genome are targeted to characterize individuals by their DNA; at least nine sites are profiled. Our example uses only one site.

Describe a crime scenario to the students involving some of the characters from the Parker Brother’s game CLUE. Miss Scarlet was found murdered in the library in the middle of the night by Mrs. White (maid). A candlestick lay near the body in a pool of blood. The list of suspects includes wealthy Mrs. Peacock, Professor Plum and even sweet Mrs. White. Ask the students for help to solve the crime.

Cut out the DNA sequences retaining the source label on the strip. Hand out DNA sequences to the students. Give the first 12 students the DNA sequences that includes samples from the crime scene, Miss Scarlett, Mrs. White, Mrs. Peacock, and Professor Plum. Then hand out the “general population” sequences to the rest of the students and increase the number if needed so that every student gets a sequence.

Briefly describe the structure of DNA and relate to the DNA sample strips: each letter represents a specific chemical structure called a base and the bases are linked together in two complementary strands with a sugar-phosphate backbone. We use the numbers 5’ and 3’ to orient the strands. If you have the sequence of one strand, you automatically know the sequence of the other strand via the base pairing rules, so for purposes of simplicity, we are using the sequences of one strand only.

Have students model the action of a restriction enzyme by having all the students look for the sequence “GAATTC” and cut the DNA sequence after the “G.” Explain that restriction enzymes do this job in nature.

Tell the students that they have created DNA fragments from their original DNA sample. Tell them to 1) count the number of fragments they have and 2) the size of each fragment (count # letters in each fragment). They can place their values in the table below.

Collect the data from the students and fill in the numbers on an overhead sheet. You can make a table similar to the sample below. (At this point, you might ask students why there are two sets of fragments for each person and remind them that each person has two alleles for every gene locus.)

Then create a diagram of a gel, put each sample of fragments into the gel, and separate the fragments by size according to the diagram (see results diagram below). Now students can see which fragments found at the crime scene match with victim’s fragments and with a suspect’s fragments. You eliminate the fragments that match with the victim. Looking at the remaining fragments from crime scene, see if you can match the fragments to the pattern of one of the suspects. Every fragment remaining in the crime scene sample must be found in the suspect’s sample or you do not have a match. At this point you should have a suspect that matches the crime scene sample.

Now address the question of the probability of the crime scene sample match NOT coming from the suspect. Take data from students holding “general population” DNA samples: have them tell you the number of fragments they have and the size of each fragment (count # letters in each fragment). Put this data into a table.

Use the product rule to calculate the probability of another person having the same DNA pattern as the suspect at multiple sites: the probability of multiple events occurring simultaneously is obtained by multiplying the probabilities for the occurrence of each event.

Discuss some drawbacks to this method (chain of custody). In other words, DNA fingerprinting can show that a DNA sample is very likely to have come from a specific individual, but it does not show HOW the DNA arrived at the crime scene.

Identity of samples	fragment sizes	number of students with this pattern	probability of seeing each pattern
crime scene sample	13, 7 10, 5, 5 2, 18 8, 12
Mrs. White	2, 18 8, 12
general population	13, 7
(sample size = ? )	10, 5, 5
	2, 18
	8, 12
	6, 4, 10
	3, 10, 7
	1, 19

General population

5' GAATTCCCATACGAGTTCCC 3'

Mrs. Peacock

5' GAATTCCCATACGAGTTCCC 3'

General population

5' GGAATTCCATACGAGTTCCC 3'

crime scene

5' GGAATTCCATACGAGTTCCC 3'

General population

5' GAATTCCCATACGAGTTCCC 3'

General population

5' GGAATTCCATACGAGTTCCC 3'

Mrs. White

5' GGAATTCCATACGAGTTCCC 3'

General population

5' GGGAATTCATACGAATTCCC 3'

Professor Plum

5' GGGAATTCATACGAATTCCC 3'

General population

5' GGGGAATCATACGGAATTCC3'

Professor Plum

5' GGGGAATCATACGGAATTCC3'

General population

5' GGGATTCCATACGAATTCCC 3'

Miss Scarlett

5' GGGATTCCATACGAATTCCC 3'

crime scene

5' GGGATTCCATACGAATTCCC 3'

General population

5' GGGGGAATTCACGAGAATTC3'

Miss Scarlett

5' GGGGGAATTCACGAGAATTC3'

crime scene

5' GGGGGAATTCACGAGAATTC3'

General population