Genetics
Unit 3 IP - DNA Profiling 1. Explain the use(s) of DNA profiling, and describe at
least 1 benefit and 1 drawback.
DNA profiling is a molecular biology technique that can provide helpfull information in many
areas such as parentage testing and criminal investigation. Unless there is a reason to do DNA
profiling such as knowing who are your parents DNA profiling is not very useful. Today there
are many other kinds of DNA analysis, i.e. diseases predisposition, ancestry ecc ecc
Benefit
The process can be used to identify potential suspects and link suspects to a crime,
proving they were at a certain place. DNA profiling also enhances the criminal system's
accuracy.
Drawback
It is a complicated and tedious process, at times giving results that are hard to
interpret.
2. Describe the steps involved in creating a DNA profile.
Extraction
DNA is located within the nucleus of cells throughout the body and the extraction step is
responsible for breaking open the nucleus and releasing the DNA molecules into
solution. During this step it is also possible to separate the DNA molecules from all
other cellular material and any other debris that may be present in a particular biological
sample. Some of these materials can be potential “inhibitors” to steps later on in the
DNA testing procedure so it is important to try and isolate only the DNA molecules.
Common inhibitors commonly found in forensic cases are hemoglobin and indigo dyes
from denim. Two common methods of extraction used at the BCA are a manual PhenolChloroform (otherwise known as Organic Extraction) and through the use of a robotic
system called the Maxwell® 16. Running samples on the Maxwell® 16 takes a
minimum of two hours and samples extracted manually using the Phenol-Chloroform
method takes a minimum of three hours.
Quantitation
One of the standards all DNA testing laboratories must meet is to ensure that the DNA
recovered from an extraction is human rather than from another source such as
bacteria. This is done through quantitation where the quality and quantity of DNA
present in a sample is measured and assessed. Additionally, determining the amount
of DNA in a sample is essential for success in the next step since most amplification
systems require a narrow range of input DNA. This step is completed at the BCA
through the use of a purchased Quantifiler DNA Human Quantification Kit and then
running all samples on an instrument known as the ABI PRISM 7500 Sequence
Detection System. This process takes approximately 30-60 minutes to set-up and then
approximately two hours to run on the instrument.
Amplification
DNA amplification is accomplished through the use of a technique known as
Polymerase Chain Reaction (PCR). PCR is a process in which millions of copies of a
specific sequence of DNA can be made in a matter of only a few hours. This is
important for forensic DNA samples since the DNA often found at crime scenes is
limited in both quantity and quality. This molecular “xeroxing” process is completed by
precise heating and cooling of the samples in a thermal cycling pattern for
approximately 28 cycles.
The amplification kit used by the BCA amplifies 15 different regions of DNA as well as a
sex-determining marker. The BCA uses a purchased AmpFlSTR Identifiler kit and
then the samples are run on an instrument known as the GeneAmp PCR System
9700. This process takes approximately 15-30 minutes to set-up and then
approximately three hours to run on the thermalcycler instrument.
Capillary Electrophoresis (CE)
After the PCR reaction is completed it results in a large mixture of amplified DNA
molecules which need to be separated in order to distinguish the various molecules
from one another. This is accomplished through a process known as capillary
electrophoresis. DNA molecules carry a negative charge and once an electric current is
applied to the sample the molecules enter a very thin capillary filled with a gel-like
polymer and migrate towards the positive anode at the other end of the capillary. The
PCR products are then separated by size because the smaller DNA molecules will have
an easier time migrating through the polymer than the larger DNA molecules. The data
from this process is then collected on a computer attached to the CE instrument and
then through the use of a software program a DNA profile is developed. The BCA uses
an instrument called the ABI Prism® 3130 Genetic Analyzer which is capable of
analyzing four samples at a time. Set-up for this step takes approximately 10 -15
minutes and each injection on the 3130 takes approximately 45 minutes.
3. Although DNA profiling services are attractive because they can reveal “your unique ethnic
background, and match you with newfound relatives” (MyHeritage, 2021). Such data can also be used
for criminal profiling, such as what happened in the case of the Golden State Killer. Describe at least 1
psychological, cultural, or social factor that can influence an individual's decision to have their DNA
analyzed, knowing not only that the information may be useful but also that the results may not be
private.
4. Getting a clean and clear DNA profile can be influenced by the source of the sample. Researchers
have tested various approaches and developed different kits for extracting the DNA from a sample and
generating a profile. The table below compares two such DNA kits. If you were an investigator, address
the following using only the data that are shown: a. Which kit would you choose if all you had was a
cigarette butt? Explain why. b. Would you choose the same kit if all you had was a coffee cup? Explain
your rationale. c. If you only had DNA Kit 1, what sample source would be the best to work from (e.g.,
blood swab, saliva, or clothing)? Explain why. Comparison of Two DNA Kits for % Successful