21.5 Genetic fingerprinting Flashcards
What fact is genetic fingerprinting based off of
Every individual has different DNA
(except identical twins)
What part of DNA does genetic fingerprinting rely on
The introns (non coding DNA)
Because 95% of humans DNA doesn’t code for a protein but is still functional
What are DNA bases that are non coding known as
How do they differ between individuals
Variable number tandem repeats
(VNTRs)
For every individual, the number and length of them has a unique pattern so are different in all individuals.
The more closely related individuals are the more similar the VNTRs
The process of genetic fingerprinting has 5 stages, what are they
Extraction
Digestion
Separation
Hybridisation
Development
How does extraction occur in genetic fingerprinting
Even the tiniest bit of animal tissue will work, eg a drop of blood or a root hair cell
So extract the DNA by separating it from the rest of the cell
Use polymerase chain reaction to clone it and increase the quantity of it
How does digestion occur
The DNA is cut into fragments using the same restriction endonucleases
So these can cut close to but not within the target DNA
How does separation occur of DNA
Process of gel electrophoresis
Fragments of DNA are separated out according to size through gel electrophoresis:
The gel is immersed in alkali to separate double DNA strands into single ones
- DNA fragments are placed on agar gel and a voltage is applied across it
- The resistance of the gel means that large fragments take longer to travel across it
So this separates DNA strands of different lengths
Then they’re transferred from gel to nylon membrane
How does hybridisation occur to these separated DNA strands
Radioactive DNA probes are now used to bind with the VNTRs
The probes have complimentary DNA base sequences to VNTRs so they bind to them under specific conditions eg temperature and PH
So DNA probes added onto the nylon membrane
How does development occur to the DNA strands
Xray film is placed over the nylon membrane
And film is exposed by the radiation from the radioactive probes
A series of bars is revealed as these points correspond to position of DNA fragments as separated during electrophoresis
Pattern of bands is unique to every individual
How is DNA fingerprinting used
Eg at crime scene you can get the DNA fingerprint from suspects and from blood at the crime scene
If there is a match the pattern of bars is sent through an automated scanning machine
This calculates the length of DNA fragments from the bands. It does this by using data taken by the distances travelled by electrophoresis by known lengths of DNA
How is genetic fingerprinting used in paternity tests
The DNA of an individual is half the DNA from mother and half from father
So every band on the DNA of individual should have a corresponding band with either the mother or fathers banding
How is genetic fingerprinting used to determine genetic variability in a population
The more closely related two individuals are the closer the resemblance of their genetic fingerprints
So if a population has members with very similar fingerprints, there is very little genetic diversity
The DNA at a crime scene matches the DNA of an individual
Why doesn’t this always mean they’re the murderer
- The DNA was left at another occasion
- DNA could belong to a very close relative
- DNA may have been contaminated after the crime either by suspects DNA or chemicals
There is a chance that the DNA of the victim matches that of the suspect, eg if they’re from a very small community/ethnic group
How does genetic fingerprinting work for diagnosing disease eg Huntingtons
Huntingtons disease means a 3 base sequence is repeated over and over again more than 38 times.
Normal people have repeats less than 30
So cut sample of DNA from individual with Huntingtons with restriction endonucleases and then DNA fingerprint can be prepared
This fingerprint can be compared with individuals who may have the disease to test for it
How is genetic fingerprinting used in animals and plants
It can also identify plants or animals that have a particular allele of a desirable gene
It can also be used to prevent undesirable inbreeding
