(A) The block duplication (BD) model. Assume (ancestral) seven genes in a chromosome region. After one BD (D = 1), four duplicate genes are lost (L = 4). In this case, no translocation (T  = 0). Thus, the total number of genetic events is G = 1 + 4 + 0 = 5. (B) The tandem duplication (TD) model. There are two chromosome regions with four and three genes, respectively. After three TDs (D = 3), one copy in each duplicate pair is moved to another chromosome by translocation (T =3), and no gene loss (L = 0). The total number of genetic events is G = 3 + 0 + 3 = 6.