 In texonomic studies we use different types of molecular markers. One of such marker is protein markers which is also known as biochemical marker. This type of markers are available since 1950s. In these types we use protein and amino acid bending pattern to compare the differences in the amino acids and proteins among different individuals. In this technique we study variations in different individuals because in different individuals the sequence of amino acid varies. Similarly the bending pattern of proteins varies. Now when we compare the protein with gel electrophoresis we conclude that the proteins from the samples are closely related to each other. But if the bending patterns of different samples are different from each other then we assume that the samples we took from the proteins are distantly related. We can easily separate the proteins through the gel electrophoresis and we can note their bending pattern. Using this technique is beneficial because we use simple equipment in it. And this technique is the best example of comparison of morphological characters. They have a disadvantage. For example, the proteins or the protein markers are more affected by the environmental factors. Similarly, the protein markers have very little availability. They are available in limited numbers. This is why we cannot use these types of markers in the entire organism. The next type of markers are non-PCR based markers. There is an important type of restriction, fragment, length, polymorphism. This technique was introduced by Boston in the 1980s. Through this technique, we study the genetic variation in the organisms. Because different individuals have a genetic variability. All these organisms are closely related and have a less genetic variability. And the organisms that are distantly related have a higher genetic variation. If we have samples of different animals, we can compare their RFLPs and estimate whether the unknown samples are closely related or distantly related. The RFLPs are used by the molecular markers of different species. The first marker that was introduced was this one. Now, what do we do in this technique? In this technique, we exploit the restriction sites. That is, we compare the restriction sites of different organisms. Now, what are restriction sites? Restriction sites are basically DNA sequences. These DNA sequences can have 4 to 6 base pairs. If these 4 to 6 base pairs are cleaved with a specific enzyme, then these different fragments are produced. Now, we can compare these fragments. If we look at this slide, in the first step, we have cleaved the restriction sites through restriction enzymes. In the next step, we have separated the different fragments from the agarose gel. After that, we transferred this band to the nitrocellulose membrane. After that, in the next step, we used radioactive probes through southern blotting. These radioactive probes, these restriction sites, when the fragments are attached to a specific place, then we use X-rays in the next step. In this way, we compare the variations of the restriction sites of different individuals. Now, these organisms, which are closely related to the restriction sites, also have similarity. These organisms, which are distantly related to the restriction sites, have differences. Similarly, the PCR-based molecular markers can also be used to compare organisms. We can find out whether these are closely related or distantly related organisms. Different PCR-based techniques used are Random Amplified Polymerase, Polymorphic DNA, ISSR Inter-Simple Sequence Repeat, SSR Simple Sequence Repeat, AFLP Amplified Fragment Length Polymorphism, EST Express Sequence Tags, and SCOT Stop Codon Targeted Marker. These are different PCR-based markers used to compare organisms or individuals.