Answers to Questions in Appendix C Exercise I Questions 1–4: In each question, another locus is added to the genotype. As a result, the number of siblings with the same genotype as the responding student should decrease with each question. The exact numbers of identical siblings and the specific pattern of decrease will differ from student to student and class to class, but the downward trend should be the same. Question 5: How do your results demonstrate the principle of increasing power of discrimination used in forensic DNA profiling?
As the number of genetic loci increases, the number of included individuals decreases. Question 6: If more than one child shared the same genotype, what possible explanations are there?
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Identical twins
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Chance occurrence. With only 4 alleles this remains a possibility; as the number of loci increases, chance matches are less and less likely.
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Clones!?!?
Exercise II Question 1: What do you notice about allele frequencies between populations? Is there any specific trend?
Allele frequencies may be different between different ethnic populations. There are no specific trends. Question 2: Forensic laboratory genotyping results often report random match probabilities for specific populations. Use the data in your chart to explain why this might be important. Hint: remember that the match probability is used to provide some indication about the "pool" of potential people with the same genotype as a suspect.
The random match probability may be different for different populations. Random match probability is most relevant for the same ethnic group as the individual under study, and it is important to know that the proper control group has been used for comparison. Discussion questions: 1. Imagine that blood, known to come from a criminal, was left at the scene of a crime, collected, and typed for the 13 CODIS loci. No suspect has been arrested, and there are no good investigative leads. Do you think that genotypes at the 13 CODIS loci should be used to make conclusions about the race of any potential suspect? Use what you have learned from the STRBase tables to support your position.
Genotypes at the 13 CODIS loci should not be used to make any inferences about the race of a potential suspect because there are no alleles that uniquely identify any specific racial group.
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