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Why is PCR used?
Why is PCR used?
To amplify a DNA sample, e.g. one found at the crime scene so further tests can be conducted on it. 

Advantages and disadvantages of in vitro cloning VS advantages and disadvantages of in vivo cloning: 

PCR is automated, making it rapid and efficient. It is particularly valuable for forensics. It also does not require living cells, so no complex culturing techniques that require time and effort are needed. 

PCR requires a very pure sample, any contamination is also amplified and can lead to false results from further testing etc. It is also less accurate, and any errors in copying DNA are also copied in the subsequent cycles. 

In vivo cloning is particularly useful when the main objective is to introduce the desired gene into an organism, e.g. introducing the vector to a human. Additionally, it involves almost no risk of contamination as the desired gene has been cut using the same sticky ends so contaminant DNA will not be taken up by the plasmid. Very accurate, the chances of a mutation are very rare. It also cuts out a specific gene, so not the whole DNA sample is being replicated. It also produces transformed bacteria, which is useful if the main objective is to produce proteins commercially/ medically e.g. insulin. 

In vivo cloning is very time consuming. It could take many days or weeks to produce the same quantity of DNA that PCR would in a shorter time.
How can specific alleles of genes be detected in a person’s DNA?
How can specific alleles of genes be detected in a person’s DNA?
Using DNA probes, which are short, single-stranded lengths of DNA with labels attached to it, such as fluorescent dyes or radioactive labels, e.g. 32P. First, a DNA probe must be made that is complementary to the sequence of the allele being investigated. This is then multiplied using PCR so there are many copies of the probe. A marker, such as the fluorescent dye or radioactive label is added to the DNA probe. Then, a sample of DNA from the individual is retrieved and heated to separate the two DNA strands. The separated strands are then cooled in a mixture containing the DNA probes. If the DNA sample contains the allele, the probe has a high chance of binding to it as the base sequence is complementary to the base sequence of the allele. The DNA is washed clean of any unattached probes. The remaining hybridised DNA will be labelled, either fluorescently so will fluoresce under specific conditions, or radioactively, where an X-ray film is exposed to the DNA and so the radioactivity will be picked up by the film.
Uses of DNA Fingerprinting:
Uses of DNA Fingerprinting:
Used for paternity testing, as the more closely related two individuals, the greater the resemblance between their genetic fingerprints. 

They can be used in forensics, to see which suspect may have been at the crime scene by comparing the DNA found at the crime scene against the DNA of suspects. 

They can be used in medical diagnosis, e.g. Huntington’s Disease, which is a genetic disorder determined by the number of repeats of a particular base sequence. The DNA of the patient can be compared against those who are affected or unaffected by Huntington's. Genetic fingerprints can also be used for diagnosis, such as comparing the DNA fingerprint of a microbe found in a patient against DNA fingerprints of known organisms. 

It can be used for artificial selection, such as identifying plants or animals with a desirable gene so they can be bred in order to increase the probability their offspring also having the characteristic.