Genetic fingerprinting Flashcards
What are VNTRs?
95% of human DNA is made up of introns which consist of many variable number tandem repeats (VNTRs)
The probability of 2 individuals having the same VNTRs is very low + the more closely related you are, the more similar the VNTRs are
Genetic fingerprinting is the analysis of VNTR DNA fragments + can be used to determine genetic relationships + the genetic variability within a population
Stage 1- Extraction
DNA is extracted from the sample
If the DNA is small its quantity can be increased using PCR
Stage 2- Digestion
Restriction endonucleases are added to cut the DNA into smaller fragments
Stage 3- separation (gel electrophoresis)
- Fragments are separated according to size by gel electrophoresis
- DNA samples are loaded into small wells in agar gel which slows the movement of molecules + an electrical gradient is set up
- DNA has an overall negative charge so moves towards the positively charged end of the gel
- Smaller pieces of DNA can move faster + further along the gel + this is how different lengths of DNA are separated
- An alkaline is then added to separate the double strands of DNA
Stage 4- hybridisation
DNA probes are added to bind with VNTRs. DNA probes are short, single-stranded pieces of DNA complementary in base sequence to the VNTRs. They are radioactively + fluorescently labelled
Different DNA probes are mixed with the single-stranded DNA VNTRs on the agar gel for them to bind
Stage 5- development
- VNTRs + DNA probes are transferred to a nylon sheet
- The nylon sheet can be exposed to x-rays to visualise the position of radioactive gene porbes, or UV light if fluorescent probes were used. Development of the X-ray film reveals dark bands where the DNA probes have attached
Uses of genetic fingerprinting
- Forensic science to place suspects at crime scenes
- For medical diagnosis
- To ensure animals + plants are not closely related before being bred - reduce the risk of passing on harmful genetic conditions
