Transition and Transversion - what is the difference?

Transversion, in In genetics, refers to the substitution of a purine for a pyrimidine or vice versa. It can only be reversed by a spontaneous reversion. Because this type of mutation changes the chemical structure dramatically, the consequences of this change tend to be more drastic than those of transitions. This is because the wobble position of the DNA, which to a large extent is responsible for the degeneracy of the code, is more tolerant of transition than a transversion, such that a transition mutation is more likely to lead to the same amino acid being encoded for. Transversions can be caused by ionizing radiation and alkylating agents.
In genetics, a transition is a point mutation that changes a purine nucleotide to another purine (A ↔ G) or a pyrimidine nucleotide to another pyrimidine (C ↔ T). Approximately two out of three single nucleotide polymorphisms (SNPs) are transitions.
Transitions can be caused by oxidative deamination and tautomerization. Although there are twice as many possible transversions, transitions appear more often in genomes, possibly due to the molecular mechanisms that generate them.
5-Methylcytosine is more prone to transition than unmethylated cytosine, due to spontaneous deamination. This mechanism is important because it dictates the rarity of CpG islands.