The three letters stand in for a description of the mutant phenotype. In this example, you don't know what that phenotype is, nor do you need to. We will use the same letters but all in unitalicized caps to indicate when a mutant phenotype is expressed. For example, the genotype Xaaa/Y;Bbb+/Bbb;ccc+/ccc would be a male that exhibits AAA and BBB.
X Pig / Y ; rat pln / rat pln+ ; Eka+ / Eka+ ; Dwo / Dwo