Actually Paul, there are 4 clades (groups) of B genes (the total number of B genes varies in different orchids). Genes of clade 1 and 2 are expressed in the outer tepals, 1,2 and 3 in inner tepals and 1,2,3 and 4 in the lip. The capital T and small t , has nothing to do with the genes, it is just used to denote the tepals, capital for the outer, small for the inner tepals. It is much more complicated because these different B gene clades autoregulate the expression of one another. For eg. The clade 1,2 genes do no allow the clade 3 and 4 genes to be expressed outside the inner tepals and the lips. This is a natural feedback mechanism, but due to repeated mericloning (vegetative reproduction, no sexual reproduction) the mutations accumulate such that one of the gene clades either looses its function completely or partially, thus giving rise to these peloric mutants.