Evolution of Globin Expression in the Genus

Comparison of electrophoretic globin phenotypes of 18 different Xenopus taxa reveals four different basic types of banding patterns. Each type includes species that also are similar in their morphological, cytogenetical, and biochemical characteristics. Three of these patterns reflect distinct evolutionary lines, while the fourth may be interpreted as the intersection of two of these lines. The composition of the basic pattern of the highly polyploid species is consistent with an allopolyploid origin of most of these species. The number of distinct globin polypeptides-four in the only extant diploid species, X. tropicalis, and five or more in most of the tetraploid species, including X. laevis-suggests that primordial globin genes had undergone duplication either before or after the tetraploidization event. Finally, the individual globin phenotypes are excellent molecular markers that are of great help in identifying the various species but not the subspecies.