DNA Profiling

Write a brief description of the difference between RFLP and STRs

-RFLP (restriction fragment length polymorphism)- it indicates a difference between samples of homologous DNA molecules via restriction enzymes

-STRs (short tandem repeats)- they consist of short repeated sequences of DNA (2-8 nucleotides) and are located on non-coding regions of chromosomes. STRs are also polymorphic, which means that there are nine or more different types of alleles that can be detected.

-The STR and RFLP methods differ in DNA profiling and the STR has more advantages, which is why it is preferred today. While the STR only needs a very small amount of DNA to run, the RFLP does not as it requires a very large sample of DNA to work. Therefore, with a small amount of DNA, using the STR method reduces the likelihood of destroying sample due to the utilization of PCR. On the other hand, the RFLP method destroys the cell after it is completed. Furthermore, the STR method takes only around a couple hours to complete whereas the RFLP method could take weeks. STR is also more accurate than RFLP because STR targets specific sites unlike RFLP.

How many STRs does the FBI use to analyze?

-They use 13 different STRs, with repeats of four or five nucleotides, plus sex markers

Describe how PCR is used in DNA profiling

-PCR is used to amplify the specific regions of the DNA (STRs) and is therefore used to ultimately detect differences between STRs. During PCR, DNA fragments, with primers, are heated and cooled to activate primers and DNA polymerase in copying the fragments over and over again until the amount of copied fragments are "amplified"

Describe how electrophoresis is used in DNA profiling

-Electrophoresis is used to separate different DNA fragments (which were amplified with PCR) by putting the fragments onto polyacrylamide gel. The polyacrylamide gel in PCR separates different DNA fragments by size and the smaller the fragment, the further it travels through the gel.

Explain how the probabilities of having a specific set of STRs is extremely unlikely. Therefore if yours is present at a crime scene, what does that mean?

-The probability of having a specific set of STRs is extremely unlikely because one in every 10^-100 quadrillion share the same STR profile. The number is greater than the number of humans that ever lived, therefore each STR profile is specific to one person. If my STR is present at a crime scene, this means that you were definitely at the crime scene but does not guarantee any more than that.