Hi Karoly,

Sounds like a great prac - I love the idea of getting the students involved in wet lab work!

I'm afraid I don't know of any "whodunnit" style experiments as you propose, but I can propose a potential alternative experiment for you. The Natural History Museum at Oxford University runs a great day-long, wet-lab experiment for local secondary schools that I used to volunteer for, and which sounds like it might be up your alley.

Briefly, it involves the students testing their ability to taste a bitter compound - some come up as not tasting anything, some as partial tasters and some as very strong. The students then amplify a small PCR product from a gene for a bitter taste receptor (I can't remember which, sorry). This PCR product contains a SNP which encodes either for a taster or non-taster allele and also conveniently represents an RFLP. When the students digest their PCR product with the relevant restriction enzyme and run the DNA on a gel they can see whether they are genotypically homozygous taster, non-taster or heterozygous taster/non-taster. They can then compare this to their "phenotype" (their taste test at the beginning of the class) which provides plenty of good scope for discussion of genotype/phenotype relations, haploinsufficiency, sources of experimental error, biological causes of mismatch between genotype/phenotype etc. etc..

It's a really great prac and, if you have PCR machines already, doesn't cost a huge amount to set up (main costs being chelex beads, primers, restriction enzymes etc.). I believe that it was developed through a grant from the Wellcome Trust in the UK, so I'm not sure of the licensing requirements etc., but if you are interested in the practical I'd be happy to Personal Message you the contact details for the people who run it and you can find out more.

All the best,

Dan

Hi Dan, we have done the PTC stuff already. Thanks for the tip though :-).

You can Google human "vntr polymorphism kit" to find some commercially available kits for assaying a highly polymorphic human locus which will probably give a distinct pattern in each individual of your group. Note that D1S80 and D1S58 and pMCT118 are all different names for the same thing.

A cheaper alternative, if you already have the DNA extraction, PCR and gel running reagents that you need, would be just to order the primers for D1S80 (and possibly one or two other highly polymorphic VNTR sites) from IDT (see image for example of IDT ordering).

Thanks much, that might be indeed the way to go! The best, K

Performing an actual DNA extraction, dilution, PCR, followed by electrophoresis would be quite difficult with human samples in a typical high school classroom. Imitations of PCR and DNA extractions though can be fairly simple:

For the DNA extraction: Rather than using actual reagents and what not, you can make them yourself and distribute them as you wish. Students can "isolate DNA" from their hair using a specific protocol, either that you create, or find on the web. They can actually go through steps, doing the pipetting, even spinning if you have a centrifuge. They could also use pipettes to dilute the samples as you direct. Doing an actual extraction with strawberries or liver is a great alternative to trying the isolate DNA from human samples.

For the PCR: Isolated DNA can be added to a multiplex cocktail (or the individual ingredients) that you create. This cocktail can include false ingredients labeled: Forward primer (as many as you want), reverse primer (same number as forward), dH2O, Taq polymerase, buffer, and DNA. I'm not sure what you would use for a thermocycler, but from what I understand, back in the day, they would use different temperature water baths and manually move samples from water bath to water bath following a strict time regimen (Boy that makes me feel a little spoiled?).

Electrophoresis: If you have the equipment to run a gel, you could buy molecular ladders that imitate what a multiplex PCR reaction would give (Many bands in a single lane). Originally, these ladders are used to determine the size of a fragment, but here, we would use them as imitations of PCR multiplex reactions. This is how you would catch the culprit of whatever story you come up with. You would have specific lanes for suspects and at the end you would load the culprits molecular ladder, which should match one of your suspects. Running a molecular ladder is simple. There is no required heating or cooling. I prefer to keep ladders in the refrigerator, covered in tin foil.

Unfortunately, this isn't quite as cool as doing the real thing. I agree. But it would still be a good experience for any high schooler.

Thanks, K

Thanks you for all the answers and leads, you are wonderful. After some more research based on your leads, I think that David Barker is the winner! I will give it a shot with vntr polymorphisms, these 4 should give me a decent combinatorial power. I will let you know how it goes, stay tuned. The best, K

NAME: D1S80

5'-GAAACTGGCCTCCAAACACTGCCCGCCG-3'

5'-GTCTTGTTGGAGATGCACGTGCCCCTTGC-3'

Name: D21S11

5'-GTGAGTCAATTCCCCAAG-3'

5'-GTTGTATTAGTCAATGTTCTCC-3'

Name: D5S818

5'-GGGTGATTTTCCTCTTTGGT-3'

5'-TGATTCCAATCATAGCCACA-3'

Name: D8S1179

5'-TTTTTGTATTTCATGTGTACATTCG-3'

5'-CGTAGCTATAATTAGTTCATTTTCA-3'

For maybe a simple alternative why not swab some plasmid DNA on the hands of one of the students who is unknown to the others. Get him/her to commit the crime, contaminating some evidence along the way. Then take swabs of all the students hands and the evidence and PCR for the plasmid DNA. Maybe a bit artificial but it will give them PCR experience, be fun and relativly cheap.

Love it! Thanks, k