The results shown are from a DNA test for four genes used in a paternity identification case. DNA for the mother (M) and her child (C) are shown along with DNA from two possible fathers, F1 and F2. In the 'C' column, label the DNA bands contributed by the mother with 'M' and the DNA bands contributed by the father with 'F.'

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Hi, everyone. Let's look at our next problem. It does tr analysis is a powerful tool for DNA fingerprinting as it allows for high discrimination power and can be performed on small or degraded DNA samples. It has become a standard method in forensic science and is widely accepted as a reliable and accurate method for identifying individuals. Which factor can affect the accuracy of S T R analysis, choice A sample contamination B A lilic dropout C PC R stutter or D all of the above. Well, let's walk through these answer choices and think about which ones or one could affect the accuracy of this method of DNA fingerprinting will recall from our content video that S T R analysis looks at short tandem repeats that the number of repeats of these sequences is highly individual. So let's start with choice. A sample contamination. Well, this definitely can affect the accuracy of this analysis. Uh A DNA sample could be affected by being contaminated during collecting handling or in the analysis itself. I'm going to put a little dot Here, we won't pick that as our answer because we do have that choice D all of the above as an option. Uh sample contamination is particularly a risk because you only need a small amount of DNA for this type of analysis. So it really doesn't take very much to contaminate a sample. In addition DNA is very robust. So even a degraded sample, a sample that's been exposed to the elements for a long time can still provide enough DNA for that analysis. So you need very, very small amounts of foreign DNA to introduce contamination to a sample and throw off the accuracy of the results. Choice B is a lilic dropout and that's when an alley in the analysis is not detected. So it just doesn't show up when looking at the peaks, when looking at the number of repeats. And this would result in an incorrect or incomplete profile. You're just missing a peak and this could be poor sample quality or PC R failure that causes this and obviously will affect the accuracy of the analysis. So choice B we also put a dot There, if I were in a hurry, I'd go ahead and select choice D all of the above because I've already got more than one correct answer here. But to be thorough, let's look at choice C PC R stutter. And this, when this occurs, you see additional smaller peaks that are 1 to 2 repeat, shorter than the main peaks. And as evidenced in the name, this occurs when you have a problem in the PC R that results in this. Uh So you want to be careful to make sure you're optimizing your PC R conditions to minimize the possible occurrence of this. So choice C can also be a possibility. And indeed our answer here uh in terms of things that can affect the accuracy of S T R analysis would be choice D all of the above. See you in the next video.

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Key Concepts

Mendelian Inheritance and Allele Contribution

DNA Banding Patterns in Gel Electrophoresis

Paternity Testing Using Genetic Markers