Electrophoretic Evidence and Plant Systematics

Abstract

The study of phenotypes and their variation often provides evidence for phylogenetic inferences in plant systematics.Therefore, it is critical that the phenotypes analyzed reflect as directly as possible the underlying genotypes.The equation between phenotype and genotype is simpler and better understood for evidence obtained by electrophoresis of plant enzymes than for most morphological characters.This article riis the advantages and limitations of imo.yapana evidence to test hypotheses in plant systematics and evolution.It also summarizes the results of a large number of studies which have utilized this evidence.Three general 1 pe these studies are: (1).Conspecific plant populations are "ari similar genetically as pou by their very high mean genetic identities, 0.95 + 0.02.This result suggests that one a few populations often constitute an adequate sample of a species.775 e sini species have strikingly reduced mean genetic identities, 0.67 + vever, certain pairs of annual plant species have genetic identities similar to those of pan i 5 In these cases, the species have been shown to be related as progenitor and derivative with the derivative being of recent origin.( The amount of genetic variability within plant populations appears closely correlated with their breeding system, with outcrossing populations substantially more variable than inbreeding ones.The article 7 describes a number of actual and potential applications of electrophoresis in plant systematic Evidence obtained by electrophoresis of enzymes has not been widely utilized by plant systematists although it has dominated the research of many of their zoological poa po and population geneticists ( Manwell & Baker, 1970;Lewontin, 1974; 1975; Ayala, 1976).This has meant that the strengths and weaknesses of s eni for solving systematic and evolutionary questions in plant biology have not been sufficiently discussed.The present article is designed to facilitate an efficient evaluation, and emphasizes the unique characteristics of electrophoretic evidence, the requirements for its analysis, and actual and potential applications in plant systematics and evolution. ELECTROPHORETIC EVIDENCE; ADVANTAGES AND LIMITATIONSThe systematist analyzes phenotypes and their variation and often uses this evidence for phylogenetic inference.Such inferences require that observed phenotypes have a specifiable relationship to unobserved genotypes.The equation between phenotype and genotype is simpler and better understood for electrophoretic evidence than it is for evidence obtained from morphological characters or chromatographic comparisons of secondary metabolites.This follows from the colinearity of amino acid sequence and nucleotide sequence as well as the specificity of enzyme catalysis.It also reflects the fact that electrophoretic evidence is used to answer a very different kind of question than has usually been posed by systematists.kaysa as analysis answers a question such as: Are flower petals with