Fig. 3

Definition of transitions and transversions. Nucleotides A and G (orange circles) are in the purine family. Nucleotides C and T (green squares) are in the pyrimidine family. When alleles of a genotype are both from the same family (both purine or both pyrimidine), the genotype is called a transition (blue arrows). When alleles of a genotype are each from the opposite family (one purine and pyrimidine), the genotype is called a transversion (red arrows)