what is a shared derived charterer and how is it useful for constructing a phylogeny ? Solution Phylogeny can be understood as the science of developmental history of an organism with respect to other organisms. Since the origin of an individual remains unknwon and developmental characters can be measures only relative to other known organisms, the science of phylogeny is based upon relavance of the features of a developing organism with respect to other organisms whose features have been already well studied. For this purpose, the extent of relatedness and differences between two or more organisms are generally studied. There are some features which remain exclusive for a species whereas some features are common in different species. These common features are termed as \'shared derived characters\' because it is supposed that owing to their presence, anatomical relavance and similarities in physiological function in different species, these features must have been orginated from a common ancestor and gradually shared by different species for development. Thus, the more is the number of shared derived characters between two or more species, the more likely is their evolutionary relatedness. For example, while constructing a phylogeny tree, the index of these shared derived characters remains highly useful. It helps in grouping and clssifying organisms based upon their evolutionary history and evident relatedness based upon number of shared characters. For example, all organisms with jointed feet are placed under phylum arthropoda. After that, organisms with paired feet and un-paired feet are differentiated either as millipeds or centipeds. After that, organisms are differentiated based upon their mouth structures and so on. Thus, the occurence of jointed feet, nature of feet and distribution of body plates on mouth cavity represent shared derived characters. These characters can be further elaborated at anatomical and molecular levels. Thus, this clearly explains the role of shared derived charterer and its usefullness for constructing a phylogeny tree..