Appendix H Teacher Answer Guide Student Questions – Introduction 1. What kinds of materials obtained from a crime scene might contain DNA, and where might you find them at a crime scene?
Any kind of biological material – blood saliva, skin, hair, or bone are examples. These can be found on drinking glasses (saliva), a hairbrush or toothbrush (hair and skin), bloodstains, etc. 2. Why do you need to perform PCR on DNA obtained from a crime scene?
Probably nothing. The amount of DNA extracted from evidence is so small that in most cases it cannot be seen without some kind of manipulation (PCR amplification for example) first. 3. What might you see if you ran a DNA sample extracted from evidence on a gel before running PCR?
Usually very small quantities of DNA can be extracted from evidence obtained at crime scenes. PCR is performed to make enough DNA for analysis. 4. What is a genotype?
A genotype is a person's own genetic makeup. Usually, it's a snapshot of genetic information from different loci scattered across the genome. 5. What is the difference between an allele and a locus?
A locus is a particular location on a chromosome. An allele is a particular variation of any individual locus. 6. Why do forensic labs analyse non-coding DNA and not genes?
Non-coding DNA is used for forensic analyses because it does not carry any information about gene expression patterns. By general agreement within the forensic community, these sequences are preferred, because they only provide information about relatedness, and say nothing about a person's biological state (for example health, mental well-being, or physical state).
Lesson One: Setting up PCR Reactions 1. What does PCR allow you to do with DNA?
PCR allows you to make enough copies of DNA to perform analysis. 2. What components do you need to perform PCR?
A template, DNA polymerase enzyme, nucleotides (dNTPs), primers, and buffer (containing Tris, salt, etc.). 3. What is in the master mix and why do you need each component? •
Taq polymerase – a polymerase that is not sensitive to heat. It "sews" together the deoxynucleotide triphosphates to make a new DNA strand that is complementary to the template.
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Deoxynucleotide triphosphates ATCG – used to make the complementary strand.
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