B7. Genetic Fingerprinting Flashcards
The principles of genetic fingerprinting
Not all of an organism’s genome (all the genetic material in an organism) codes for proteins. Some of the genome consists of _________ ________ ________ _______(VNTRS)-base sequences that _____ code for proteins and repeat next to each other over and over
The number of times these sequences are repeated differs from person to person, so the length of these ____________ in _____________ differs too.
The repeated sequences occur in lots of places in the genome. The number of times a sequence is repeated (and so the number of nucleotides) at different places in the genome can be compared between individuals—this is called _________ _____________. The ____________ of two individuals having the same genetic fingerprint is very low because the chance of two individuals having the same number of _______ at each place they’re found in ____is very low.
Not all of an organism’s genome (all the genetic material in an organism) codes for proteins. Some of the genome consists of variable number tandem repeats (VNTRS)-base sequences that don’t code for proteins and repeat next to each other over and over
The number of times these sequences are repeated differs from person to person, so the length of these sequences in nucleotides differs too.
The repeated sequences occur in lots of places in the genome. The number of times a sequence is repeated (and so the number of nucleotides) at different places in the genome can be compared between individuals—this is called genetic fingerprinting. The probability of two individuals having the same genetic fingerprint is very low because the chance of two individuals having the same number of VNTRS at each place they’re found in DNA is very low.
Producing genetic fingerprints (12 steps)
Step 1-PCR is used to make DNA fragments
- A sample of DNA is obtained, e.g. from a person’s blood, saliva, etc.
- PCR is used to make many copies of the areas of DNA that contain the VNTRS
- Primers are used that bind to either side of these repeats and so the whole repeat is amplified (copied many times).
- Different primers are used for each position under investigation. You end up with DNA fragments where the length (in nucleotides) corresponds to the number of repeats the person has at each specific position
- A fluorescent tag is added to all the DNA fragments (usually to the primers) so they can be viewed under UV light
Step 2-Separation of the DNA fragments by gel electrophoresis
- To separate out DNA fragments, the DNA mixture is placed into a well in a slab of gel and covered in a buffer solution that conducts electricity
- An electrical current is passed through the gel - DNA fragments are negatively charged, so they move towards the positive electrode at the far end of the gel.
- Shorter DNA fragments move faster and travel further through the gel, so the DNA fragments separate according to length and this produces a pattern of bands
Step 3-Analysis of the genetic fingerprints
- After the gel has been running long enough, the equipment is turned off and the gel is placed under a UV light.
- Under the UV light the DNA fragments can be seen as bands. These bands make up the genetic fingerprint
- A DNA ladder may have been added to one well
this is a mixture of DNA fragments of known length that allows you to work out the length of the other bands on the gel.
- Two genetic fingerprints can be compared, e.g if both fingerprints have a band at the same location on the gel it means they have the same number of nucleotides and so the same number of VNTRs at that place it’s a match.
Uses of genetic fingerprinting (5 uses, 3,2,3,2,3)
1. Determining genetic relationships
- We inherit VNTR base sequences from our parents. Roughly half of the sequences come from each parent. This means the more bands on a genetic fingerprint that match, the more closely related (genetically similar) two people are.
- Genetic fingerprinting can also be used to look at much wider ranging genetic relationships, e.g. to see if a population of black bears found in Virginia is descended from a population in Canada or Alaska. The idea is still the same - the more bands the populations have in common, the more closely related they are.
- Sometimes you might be interested in tracing only the male or female line of descent. To look at the female line of descent you need to look at DNA in mitochondria. This is because in humans and most other organisms, mitochondrial DNA (mtDNA) is only inherited from your mum. If you’re after the male side, you need to look at Y chromosome DNA, as only men have a Y chromosome
2. Determining genetic variability within a population
- The greater the number of bands that don’t match on a genetic fingerprint, the more genetically different individuals are.
- This means you can compare the number of repeats at several places in the genome for a population to find out how genetically varied that population is
E.g. the more the number of repeats varies at several places, the greater the genetic variability within a population
3. In forensic science
- Forensic scientists use genetic fingerprinting to compare samples of DNA collected from crime scenes to samples of DNA from possible suspects, which could link them to crime scenes.
- The DNA is isolated from all the collected samples (from the crime scene and from the suspects
- Each sample is replicated using PCR. The PCR products are run on an electrophoresis gel and the genetic fingerprints produced are compared to see if any match. If the samples match, it links a person to the crime scene.
4. For medical diagnosis
- In medical diagnosis, a genetic fingerprint can refer to a unique pattern of several alleles. It can be used to diagnose genetic disorders and cancer. - It’s useful when the specific mutation isn’t known or where several mutations could have caused the disorder, because it identifies a broader, altered genetic pattern.
5. In animal and plant breeding
- Genetic fingerprinting can be used on animals and plants to prevent inbreeding, which decreases the gene pool
- Inbreeding can lead to an increased risk of genetic disorders, leading to health, productivity and reproductive problems.
Since genetic fingerprinting can be used to identify how closely related individuals are (see previous page), it can be used to identify the least related individuals in a population so that we can breed them together. - Genetic fingerprinting can also be used by animal breeders to prove pedigree. Animals with a good pedigree will sell for more money.
Tip: PCR is used to ________ the areas of ___ that contain the _________ sequences, so enough is produced for them to be seen on the ___
Tip: PCR is used to amplify the areas of DNA that contain the repeated sequences, so enough is produced for them to be seen on the gel
