In an inheritance case, a man has died leaving his estate to be divided equally between 'his wife and his offspring.' His wife (M) has an adult daughter (D), and they argue that they should split the estate equally. As a young couple, however, the man and his wife had a son that they gave up for adoption. Two men have appeared, each claiming to be the son of the couple and therefore entitled to a one-third share of the estate. The accompanying illustration shows the results of DNA analysis for five genes for the mother (M), her daughter (D), and the two claimants (S1 and S2). Do the DNA results suggest that either man is likely to be the son of the man and his wife? Explain.

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Hi, everyone. Welcome back. Here's our next problem in an orphanage. A man showed up claiming that he is the biological father of a certain child. A laboratory laboratory conducted genetic testing to investigate his claim. Which of the following results would confirm that he is indeed the child's father choice A, the P I values of all genes are less than one choice. B, the C P I is zero. Choice C the P I value should all be one or choice D, the C P I should be greater than 101 100. Well, as we think about genetic testing for paternity, we have two different values we're talking about in our answer choices. We have P I and C P I. So let's recall what these are P I is paternity index. So this paternity index refers only to a single marker. So a single locus and it is essentially a probability that a man is the father uh calculated in the format X divided by Y where X is the probability of this phenotype, this particular uh number of repeats in this marker. If the man that's being tested is the father and why is the probability of this phenotype if a random other man is the father. So that's where that fraction that generates paternity index comes from. Then we also have C P I or combined paternity index. And as you would recall looking at the name combined, and this is calculated as the product of the paternity index indices from all of the gene loci. So you take those individual paternity indices at of different markers and multiply them all together. And in this case, if the C P I is greater than 100 that indicates a greater, then 99% chance that the man being tested is indeed the father. So you're looking at multiple gene loci making sure they match up and that gives a very strong evidence, pretty good confidence that this man is indeed the father. So let's look through our answer. Choices. Choice A says the P I values of all genes are less than one. Well, we saw what the P I is is that probability that the man is the father divided by the probability the man is another random man. If this P I value is less than one, it means that the denominator is larger than the numerator. So the probability that a random other man, this father is greater. So choice A would definitely not indicate that the man is a child's father. Choice B says the C P I is zero. Well, since the C P I is expressing the probability that a given man is the father ac P I of zero would mean the man is definitely not the father. So choice B is not our correct answer. Choy C says the P I value should be all one. Well, for that P I value to be one, it means there needs to be an equal likelihood that the man is the father or that he's another random man. And so that is not going to definitely confirm that this man is a child's father. So choice C not our answer choice. So we left a twisty. The C P I should be greater than 100. Well, this is indeed the case. We saw that if that C P I is greater than 100 it indicates a greater than 99% chance that the man is the father. So that's why trust D is correct. All right, greater than 99% chance the man is the father. So our answer again is choice D, the C P I should be greater than 100. See you in the next video.

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Key Concepts

Mendelian Inheritance and Genetic Markers

DNA Profiling and Paternity Testing

Interpretation of Genetic Evidence in Legal Contexts