Question

The U.S. Department of Justice has established a database that catalogs PCR amplification products from short tandem repeats of the Y chromosome (Y-STRs) in humans. The database contains polymorphisms of five U.S. ethnic groups (African-Americans, European Americans, Hispanics, Native Americans, and Asian-Americans) as well as the worldwide population.

For forensic applications, the probability of a 'match' for a crime scene DNA sample and a suspect's DNA often culminates in a guilty or innocent verdict. How is a 'match' determined, and what are the uses and limitations of such probabilities?

Accepted Answer

Hi everyone. Welcome back. Here's our next problem in forensic applications. A match is determined by comparing, well we're talking about when we're trying to identify um D. N. A. Samples left at a crime scene and comparing them to samples from known individuals to identify who perhaps left that sample and what you compare in that are what are called D. N. A. Fingerprints. And this is done by comparing the pattern of DNA fragments from regions of DNA known to be highly variable among individuals. So there's certain regions of D. N. A. We know due to single nucleotide polymorphisms mainly are very different or highly variable among different individuals. And they can be used to distinguish individuals from each other. So you cleave the D. N. A. In with nucleus. Is that cleave it in known places. Then run those samples on a gel and look at the pattern of fragments generated. Just as you might compare fingerprints. You compare this DNA fingerprint by comparing the pattern those fragments make. So when we look at our answer choices we're going to pick choice D the fingerprints of the D. N. A. Samples and that's what that means. But let's look at our other answer choices to understand why they're not correct choice A. Says the physical appearance of the D. N. A. Samples. Well you do look at the appearance of these pattern of fragments but just seeing the appearance of the D. N. A. Sample is not sufficient. You have to actually um look for that variable region and then cleave it into fragments. So that's why that's not the correct answer. Choice B says the genetic sequence of the RNA samples well R. N. A. Is very fragile. It degrades very quickly so that's not useful in terms of forensic analysis. D. N. A. Samples. DNA is much more long lasting and stable due to its double helix. So it's D. N. A. Samples that you look at in forensic applications. Then finally choice see the blood type of the RNA samples. Um Again this is kind of we don't use our N. A. And we do use blood type and crime analysis but blood type is much less specific. We just have a handful of different human blood types as compared to the DNA fingerprints which can distinguish individual from individual due to their high variability. That's why choice C. Is not correct. So again in forensic applications, a match is determined by comparing choice D the fingerprints of the D. N. A. Sample. See you on the next video

Watch next