Explain process of Selection of taxonomic characters

Selection of taxonomic characters

Eventually classification systems may be based almost entirely on direct study of the genes themselves, but for a long time we will continue to use information for many sources. Characters useful for classifying organisms must be measurable, describable, and relatively invariable, regardless of the environment in which the organism grows. For a plant whose leaves have different shapes depending upon whether they grow in water or in air, leaf shape would not be a good taxonomic  character. For groups with good fossil records, direct measures can be made of the rates at which different features have evolved. Nucleic acid analyses and amino acid sequences in proteins, especially when combined with fossil evidence (of the splitting of groups) provide very accurate estimates of the average rate of change in genes and their direct consequences. Although the same procedures are used with all organisms, the characters upon which classification is based differ and only those characters which vary strikingly among organisms are measured. Flowering plants offer branching patterns, leaf shapes, specialised cells, reproductive structures and so on.

Many invertebrates have shells that are readily preserved as fossils and can be measured long after the animal has died. Thus taxonomic character is a feature which is present id all appropriate specimens at appropriate times. One should be very cautious in selecting useful characters. The choice of character is directly based on the accumulated experience of the taxonomist. One should select only those characters which are stable within species or groups, easily studied and quite distinctive in its easy separation from other closely related taxa. Thus a taxonomist has to search for good characters which are most effective in making the distinction and separation of the species or other taxa, quick and easy. He has to keep in mind that these characters should not show wide variation among known specimens as well as intrinsic genetic variability. Also characters should not be influenced readily by the environment but must be consistent and easily seen in the specimen.