The organization of the tadpole and adult α globin genes ofXenopus laevis

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Abstract
Adult erythrocytes of X. laevis contain six electrophoretically resolvtides globin polypeptides while tadpole erythrocytes contain four polypeptides, none of which comigrates which an adult protein. We show that three of the adult proteins are α globin polypeptides (Α α2, α3) and three are β qlobin polypeptides (β1, β2, β3). We find that a tadpole α globin gene (αT1) is linked to the major adult locus in the sequences 5‘-αT1-α2-β2-3‘ with 5.2 kb separating αT1 from α1. Another tadpole α globin gene (αT2) is linked to the minor adult locus in the sequence 5‘-αT2-α2-β2-3‘ with 10.7 kb separating αT2 from α2. These linkage relationships are consistent with the major and minor loci having arisen by tetraploidization but the different separation of larval and adult globin genes at the two loci indicates the occurrence of some additional chromosomal rearrangement. Two alternative models are presented.