by Barbara W. Heavers
Just as physiological studies of plants and animals began a new era in our understanding of species adaptations to their environment, molecular studies of organisms have led to a new era in our understanding of speciation and evolutionary relationships. We can now explore genetic variation in a population at the molecular level. We can determine the allelic frequency of genes controlling specific molecules and assess historical continuity among closely and distantly related species.
Scientists are exploring the molecular composition of a wide variety of organisms, including bacteria, plants, animals, and fungi. Molecular studies of organisms utilize separation techniques which allow the investigator to isolate several groups of organic molecules. The ability to detect differences between like molecules in individual organisms allows us to assess the variation within a species and to determine the level of heterozygosity of the population for specific alleles. Separation techniques also permit us to discover molecular differences between species and genera. It is from these molecular differences in proteins, amino acids, and base sequences of nucleic acids that we can draw phylogenetic relationships and to begin to unravel the evolutionary lines that connect or separate them.
The first group of activities in this section provide an introduction to working with molecular data. Both simulated and original data are used to compare amino acid, protein or DNA differences to construct phylogenetic trees or cladograms.
The remaining activities presented utilize paper chromatography and gel electrophoresis to separate a wide variety of molecules including demonstration mixtures, plant pigments, plant proteins, plant DNA, fish muscle proteins, and human hemoglobin. These separation techniques vary in difficulty and expense. Some are introductory and can be used in the first course in biology, but others are more appropriate for second-year biology students or independent work. These papers offer suggestions for comparative studies in species variation, responses to environmental stress, and other interspecies differences. They provide instructions and references that allow the student to work at the research level with these technologies under the guidance of an experienced teacher.
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