Profiling Techniques Flashcards
1
Q
Profiling Techniques
A
- There are times when individuals wish to find out if they are carriers of a particular disease:
- To determine if they are a carrier of a recessive disease
- To see if they are going to develop a disease that is dominant and present in the family e.g. Huntingtons
- There is a history of breast cancer in the family and the individual wishes to see if they have the gene and are more at risk of developing the disease, they can take preventative measures or more regular screenings
- In each case, the DNA sample collected is first amplified using PCR
2
Q
Electrophoresis
A
- DNA fragments are placed on a semi-solid gel
- Electrodes are placed at either end of the gel and an electric current is passed through the gel
- DNA is negatively charged and moves through the gel towards the positive electrode, away from the negative electrode
- The DNA is distributed across the gel based on the size of the fragments. Large fragments don’t travel very fast, the smaller the fragment the faster it will travel towards the positive electrode
- After a certain period of time the current is switched off, the smaller fragments as they mvove more quickly will have travelled furhter along the gel
3
Q
DNA Profiling
A
- DNA sample is treated with restriction enzymes
- These cut the DNA at particular base sequences leaving DNA in different sized fragments
- These fragments are then separated using electrophoresis
- The fragments form a pattern of bands known as a DNA profile (fingerprint)
- By examining the pattern it can be determined if the fragment associated with the faulty allele is present
- DNA profiling is also used to compare DNA samples both forensically or in a paternity case
4
Q
DNA Profiling - Forensics
A
- In the case of forensics, DNA is cut at the structural gene. The “junk” DNA between each gene is unique in its size to the individual (unique size of STR between structural genes, as some people could have the same gene)
- It is made up of a sequence of bases that repeats itself. This is called a short tandem repeat (STR)
- Comparing the sizes of the STR’s in an individual’s DNA allows with great accuracy, to determine if someone was at the crime scene
5
Q
Genetic Probes
A
- Aim to idenitfy whether or not a person has a possible faulty gene
- Need to know the base sequence for the faulty gene first
- The probe is a single strand of DNA or fragments of RNA that contain complementary bases to the faulty gene
- The probe also has a label of some sort attached. This can be a fluorescent marker or a radioactive isotope
- DNA is collected from the person and heated to cause it to denature
- The probe is then added
- If the faulty gene is present the probe will anneal (bind) to it due to complementary base pairings
- Scientists then look for the presence of the label
- Alternatively, a probe can be formed that is complementary to bases of the normal gene. If no annealing occurs, then the faulty gene must be present
