Chapter 2 Genetics of Xenopus laevis

Publisher Summary This chapter summarizes various approaches to the nuclear genome of X. laevis and discusses the methods and results that represent selected examples. A peculiarity of the genus Xenopus is that, all but 1 of its 16 to 20 species is of polyploid origin, forming a polyploid series in the proportions 2 : 4 : 8 : 12. Xenopus Laevis belongs to the tetraploid class. Evidence for tetraploidy comes from comparisons of DNA content in various species of the family Pipidae and from the fact that, in X. Laevis , a number of genes are represented by two copies, generally of less than 10% sequence divergence. On the other hand, X. Laevis shows several characteristics of a diploid species. Thus, X. Laevis displays all features of an ancient tetraploid species that is completely diploidized. If polyploidy resulted from interspecific hybridization (allopolyploidy), which presumably is the case in Xenopus , diploidization (that is, disomic inheritance) would probably have occurred at once, because interspecific divergence in genome structure could by itself prevent homoeologous chromosome pairing in newly created tetraploids. The architecture and composition of the nuclear genome as a whole, and of particular genes and gene clusters, are analyzed in detail.