 TNA mutations may be very simple and may include single base change or they may be very complex and may include several thousands of nucleotides. The simplest mutations are switches of one base for another. There are two kinds of such mutations which are transitions and transversions. Transitions are pyrimidine to pyrimidine and purine to purine substitutions such as thymine to cytosine both are pyrimidines and adenine to goanine and these both are purines. So a purine is replaced by another purine or a pyrimidine is replaced by another pyrimidine. Such changes are called transitions. While transversions are pyrimidine to purine or purine to pyrimidine substitutions such as T thymine to goanine or adenine and adenine to cytosine or thymine. So a pyrimidine is replaced by a pyrimidine or a pyrimidine is replaced by a purine. So these mutations are called transversions. Here in this picture you can see all the blue lines are transversions and all the red lines are transitions. So if T is substituted for C this is transition. If A is substituted for G this is transition. If C is substituted for G this is transversion. G is substituted for T this is also transversion and A is substituted for T this is also a transversion. Similarly A is substituted for C this is also a transversion. So these are transversions and transitions. Other simple mutations are insertions or deletions of a nucleotide of a single nucleotide or a small number of nucleotides. For example here you can see the sequence T A A C T G this is an insertion where you can see this C this was not present here in the original sequence but now it is inserted by the insertion of this single base the whole rest of the whole sequence will be frame shifted. So this will disrupt all the gene where this insertion has taken place. Similarly this is a deletion. So in this case this T which was present in the original sequence this has been deleted. So by the deletion of this T from this T onwards there will be a frame shift. So these are called deletions or insertions. All such mutations that alter a single nucleotide are called point mutations. Other kinds of mutations cause more drastic changes in the DNA such as extensive insertions and deletions and gross rearrangements of the chromosome structures. Such changes might be caused for example by the insertion of a transposon. Transposon is a sequence of nucleotide which typically places many thousands of nucleotides of foreign DNA in the coding or regulatory sequences of a gene. So this transposon may be inserted in the normal sequence of a gene. So it will disrupt that gene. For example here you can see this is a transposon and this is a full gene. This transposon can be inserted in the middle of this gene this green one portion and by the insertion of this transposon the whole gene will be disrupted and will become non-functional. So this is called a mutation. Another type of mutation which are more drastic occur at chromosomal levels. These are changes in the appearance of the individual chromosomes through mutation induced rearrangements. So there are many examples such as deletions. In the case of deletions this region is totally deleted from the chromosome. So this mutated chromosome is lacking this portion. In case of duplication this portion is duplicated here. So this mutated chromosome have double sequence particular sequence. Similarly in case of inversion this sequence has been inverted here. So the sequence is inverted on the opposite direction. Such mutations are called inversions. Similarly these are translocations. So in case of translocations a piece of chromosome may be deleted and it may attach to another chromosome. So these are called translocations as this green portion is deleted from here and it is attached here. These are translocations. So these deletion, duplication, inversion and translocation are big mutations as in contrast to the point mutations.