=DNA Profiling= DNA profiling, also know as ‘genetic fingerprinting’, is a technique that makes it possible to determine the relationship between individuals by comparing their DNA. [image:http://i.imgur.com/vAYLuSM.png] # An individuals DNA is first amplified using PCR # Then restriction enzymes are used to cut up their DNA into many different sized fragments. Because different people will have slightly different sequences, the restriction enzymes will cut at different points. Not everyone will have the same restriction sites in the same places. This results in a set of different sized fragments unique to the individual (their genetic fingerprint). These unique sets of different sized fragments are known as '''RFLPs''' = '''Restriction Fragment Length Polymorphisms'''. # These fragments can then be separated according to their size using gel electrophoresis resulting in a pattern specific to each individual (see below). # In reality there are far too many fragments and they can be difficult to see. Thus more commonly probes are made to label sequences found on only some of these fragments. ==Using Probes in DNA Profiling== When two different people have their DNA cut with a restriction enzyme each produces a very large number of different sized fragment (RFLPs). However, because the genetic differences between individual humans today is minuscule – about 0.1%, the patterns generated are still quite similar an it can be difficult to identify differences amongst so many fragment (different bands on the gel). Probes are therefore used in DNA profiling to highlight a some of the fragments that are more likely to be a different length. Probes are made made to label short repeated sequences called '''Variable Number Tandem Repeats''' ('''VNTRs''') that are commonly found in the introns (non-coding regions) Non-coding regions are naturally much more variable as they are not subject to natural selection. Mutations are tolerated as they don't affect the phenotype and thus differences between individuals are found much more frequently. Each VNTR consists of a core sequence that is repeated several times. Some core sequences are common to all individuals but the number of times they are repeated at a given site varies between individuals. Each VNTR is located at a particular site on a pair of homologous chromosomes. Though two people may share the same number of repeats at one location, the chance that they will share the same number of repeats at several locations is much smaller. Some of the fragments produced after cutting an individuals DNA with a restriction enzyme will contain these repeated sequences. These fragments tend to be vary in size due to the different number of repeats found in each person. These VNTRs make the perfect target for DNA probes. Because VNTRs consist of the same core sequence (just repeated a different number of times). Thus a single probe will highlight the different length repeats found in different individuals. Two types of VNTRs have been identified: '''''Mini-satellites''''' - sequences of (20-100 bases) repeated 0-30 times '''''Microsatellites''''' - shorter sequences (2–5 bases) repeated 5–50 times. Also called '''Short Tandem Repeats''' ('''STRs''') [image:http://i.imgur.com/O8g3FIN.png] ==DNA Profiling -Uses== [image:http://i.imgur.com/x6SM7JB.png?1] '''Forensics:''' Samples obtained from a crime scene can be compared with suspects. The advantage of DNA profiling over other tests such as blood-grouping, is that any tissue containing cells can be used as a sample and that the results are much more conclusive / accurate. This is because there is much greater variation in the genetic sequence (VNTR profile) of individuals than there is in blood groups (many people have the same blood groups). '''Paternity:''' DNA Profiling can also be used in paternity disputes to establish the true parents. This is possible as a child will have a VNTR profile that is simply a combination of elements form each of the parent’s profile.
Credit: Ben Himme