I wanted to get some input from people familiar with the process of Gel electrop

Question

I wanted to get some input from people familiar with the process of Gel electrophoresis to help interpret the data I've Gathered. The point of the experiment was to match the Crime Scene DNA sample with various suspect DNA samples to see which would match.

The following data was gathered

Marker: 11, 14, 16
CS: 13, 16, 18
S1: 16, 18, 20, 24
S2: 15, 17, 20
S3: 14, 18
S4: 13, 18
S5: 12, 16

S= Suspect, CS = Crime Scene

The data above is the measurements of how far the respective DNA samples migrated from the well to their band pattern in millimeters.

I want to say that S2 matches the Crime Scene DNA the best because there were 3 distinctive bands just like the crime scene and did not deviate that much from the measurements by more than 1 or 2 mm. Others in my group argue that either S3 or S4 are better matches because they fit within the range of the crime scene much better 13-18. The only problem I see with that is that there are only 2 bands on that DNA compared to the crime scene having 3 and S2 was the only one with 3 distinctive bands.

If anyone is wondering we didn't have a lot of time to run the experiment so we were only left with what data we gathered. We measured it and looked at it in various ways but this is the Data we could get.

So what I'm asking is what would others interpret the data? I want to say S2 but is S3 or S4 really a better match even though the band pattern is different?

Thanks in advance!

Explanation / Answer

I would say that your friends are right. I would say that the most likely suspect is S4. His DNA is the best matched in the data given. Regarding your doubt of having 3 bands and S2 being the suspect, remember all the DNA from the crime scene need not match exactly with the DNA of the suspect. A crime scene might have the DNA of both the victim and the killer. If the crime scene is a general place, it would also have the DNA of others. The crime scene markers are 13,16,18. If we take the marker of 13, it is found only in S4. If we take the marker of 16, it is found in S1 and S5. If we take the marker of 18, it is found in S1, S3 and S4. If a marker is common in two people, how do you find out who was at the crime site? Hence we search for the marker which is in the crime site and in only one suspect sample. This marker is 13. This marker is found only in S4. In addition to marker 13, he also has marker 18 which is at the crime site. The marker 16 does not belong to the supect 4 as it is not mandatory to have 3 markers each [according to your data of S3, S4 and S5]

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