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UT BIO 325L - Homework8Spring2014[KEY]incomplete

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STR DNA “Crime Scene” Analysis1. The master gel was run by the TAs and contains the samples collected at the “crime scene” (so are abbreviated as CS). Since the gels tend not to photograph well we made a schematic representation of it.a. (1) Use the schematic diagram provided to determine the genotype of crime scene samples 1, 2, 4 and 5. Fill in the chart below with that missing information.b. (1) On the diagram, draw in the missing bands for samples 7-10.CS 11 through 15 should match between the diagram and table.Missing samples from the series (e.g. CS3) did not have data on the master gel.2. (1) Everyone in your class is considered a suspect. There may be one (or more) or no criminals in each lab section so you’ll need to look at all the data. Using the class genotype data, determine the individual(s) from sections who is(are) most likely to have committed the “crimes.” Make sure to report your actual finding! It’s possible for some crime scene samples to have no suspect matches while others may have more than one. When you have your choice(s) for the primary suspect(s), indicate them all below and explain the reasons for your choices. Skip CS10 for now.No matches: CS1, CS5 – CS13, CS15CS2 = B01, Caucasian (ethnicity doesn’t need to be listed here, this is for my own notes)CS4 = D02, CaucasianCS14 = O02, HispanicThese are the main suspects because for each sample all other options could be excluded due to not matching at least one of the loci. These are the class samples that matched at all three.[CS10 potentially matches two samples since it only has data for two loci: O04, Asian and L02, Asian]3. For one of your leading suspects, determine the frequency of his or her genotype in the larger population. A table of allele frequencies is on p. 56 of the lab manual. Show your work for the following steps.a. (1) First, look up the suspect’s allele frequencies for each individual locus. Remember to use the column appropriate to their reported ethnicity. Indicate the values below.See Excel file for numbers.b. (1) Determine the genotype frequency for each locus using the appropriate Hardy-Weinberg-derived calculation.If the locus for the suspect is heterozygous (two different alleles) then the formula (from H-W!) is 2(f1)(f2). If they are homozygous it’s (f)2. Note that this can trip up students if a heterozygote has two different alleles that have the same frequency.See Excel file for numbers.c. (1) Determine/calculate the probability of having the combined genotype (matching at all three loci) of the suspect.Probability of combined genotype is found by simply multiplying together the probabilities from all three loci which they just found in part b.P = (fCSF1PO)(fTPOX)(fTH01)Differences due to rounding are fine.4. It can be helpful to translate frequencies into concrete numbers. Use your selected suspect genotype frequency to answer the following questions.a. (1) How many people out of 1,000 (of the same ethnicity) are likely to match each individual’s genotype? Out of 100,000 people?See Excel file for numbers.b. (1) Considering part a, is DNA evidence by itself more convincing or less convincing if you have a lot of potential suspects?With more suspects, the likelihood of actually finding another individual with the same genotype increases. It then becomes harder to pin down who the criminal might be, so having lots of potential suspects makes DNA evidence less convincing. (And this is why DNA evidence is usually just part of a larger case against someone!)c. (1) Consider CS10. Compared to the other samples, would you feel confident in using this sample to identify a suspect among the class? Why or why not?This question is fairly open ended, but in general the students should not be confident in using CS10. Reasons can include any (or all) of: By only having two loci, the probability of matching another individual is higher than three (this is supported by the values in the Excel sheet). The CS10 sample matches two other potential students, who do differ in the missing locus, but with the given information we couldn’t distinguish between them. The fact that the CSF1PO locus is missing in the first place is likely an indicator of a PCR or gel error, so the reliability of the data is questionable in the first place.A student could argue that using CS10 is reasonable because it does only match with two potential students and then perhaps other evidence could be used to differentiate between the them.5. (1) You know some or all of the suspects have been framed (it turns out they are just guilty of good handwriting on tiny tubes), but you cannot prove it directly. Instead, how would you argue for their innocence on their behalf (or yours if it was you!) based on the strength of the DNA evidence? Remember that DNA matching their genotype was actually found at the crime scene. You should supply at least two plausible arguments (and remember that a typical benchmark for acquittal is “reasonable doubt”).Answers will vary.If they had a high frequency from parts 3b and 3c, they could argue that it’s likely someone else did it who matched at this limited survey of loci. Also, if they had more than one suspect in the same class, that’s a good argument for doubt.Since the scene of the crime was the lab, they can make a case that they are there every week, so their DNA will be all over the room anyway, finding their DNA there isn’t a surprise.DNA evidence powerful, but not perfect. What does it mean that DNA was found there? It doesn’t mean they necessarily did anything. Without other physical or eyewitness evidence, it can be difficult to pin a crime on someone.There could have been a problem with the processing of the samples. Mislabeled, cross-contamination (PCR or even at the point of loading the gel), etc.Other answers are acceptable if accurate and reasonable.Name: ___________________________ Lab room, day, time: __________________TA name: _______________STR DNA “Crime Scene” Analysis**The compiled genotype records of the class are on Blackboard.**1. The master gel was run by the TAs and contains the samples collected at the “crime scene” (so are abbreviated as CS). Since the gels tend not to photograph well we made a schematic representation of it. a. (1) Use the schematic diagram provided to determine the genotype of crime scene samples 1, 2, 4 and 5. Fill in the chart below with that missinginformation.b. (1) On the diagram, draw in the


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