Evidence that Enzyme Polymorphisms are not Selectively Neutral

THE discovery of large amounts of electrophoretically-detectable genetic variation within natural populations has aroused considerable interest in the factors maintaining so much polymorphism. It has been proposed that these allozyme polymorphisms reflect the action of random processes^1–6, the polymorphic variation being of little or no selective significance. Alternative hypotheses have suggested that these polymorphisms may be maintained by a balance of selective forces^7–10.     

The Structure of the Anuran Amphibian Notochord and a Re-evaluation of its Presumed Role in Early Embryogenesis

For almost a century the amphibian notochord has been analyzed from either the structural or functional point of view. Relatively complete data have been collected concerning several aspects of its structure. Some of that data will be reviewed in this report. The functional role of the notochord has also occasionally been analyzed. Only recently, however, have extensive data begun to emerge which deal directly with cause-effect relationships which may or may not exist between the notochord and surrounding tissues of the embryonic axial structure system. This report will re-evaluate the role of the notochord in amphibian embryogenesis, and provide a review of the historical perspective in which recent discoveries should be interpreted.