Karyotypic analysis and evidence of tetraploidy in the North American paddlefish, Polyodon spathula

Abstract

A modal chromosome number of 120 was obtained for the ancient fish, Polyodon spathula (Pisces: Chondrostei). The karyotype consists of 48 macrochromosomes and 72 microchromosomes. The microchromosomes are like those found in certain other primitive fishes as well as in reptiles and birds. The possibility that Polyodon is a species of tetraploid origin is strongly suggested by the fact that the 120 chromosomes are easily arranged into 30 groups of four homologs each. Evolutionary comparisions are made with other primitive fish groups.