Abstract: By using the techniques of karyotype analysis and fluorescence in situ hybridization with 45SrDNA as p robe, the characteristics of karyotypes and 45S rDNA-FISH of tetrap loid and diploid in Carica papaya L. were studied. The results showed that the karyotypes of tetrap loid and dip loid were similar, the lengths of their chromosomes were 2.35 - 4.76μm as short chromosomes. They were composed of metacentric chromosomes and submetacentric chromosomes, their karyotypeswere 2A, the karyotype formulaswere 2n = 2x =18 = 16m (2SAT) + 2 sm and 2n = 4x = 36 = 32m (4SAT) + 4 sm. Two signals were detected in the karyons and chromosomes of somatic cells of dip loids, and four signalswere detected in that of tetrap loids. These signals were all located in the NucleolarOrganizer Region existed in the sixth pair of homologous chromosomes with satellites. According to the results, it is concluded that tetrap loids are homologous tetrap loidswhich came
into being as the redup lication of chromosomes of somatic cells of diploids.

Key words: Carica papaya L., Karyotype, Fluorescence in situ hybridization, Homologous tetraploid