One conceptual schema for representing the relations between markers and the clones
which are used to discover them is presented in Fig. 4, which shows the relationship of a PCR marker to a clone which contains it. The clone is related to the marker through the oligonucleotide which occurs in the sequence of the clone and which serves as the PCR
primers for the marker. A clone may have many oligonucleotides. This also shows that the graph representing the structure of a concept may not always have a tree structure.