Comparative chromosome mapping of 45S rDNA in four species of abalone

Abalone is not only precious seafood in China, but also important mariculture shellfish. In recent years, the genetic breeding research of abalone has made rapid progress, but the research data of cytogenetic analysis are still lacking. Therefore, this study used the fluorescence in situ hybridization (FISH) to compare the distribution of 45S rDNA clusters in Haliotis discus hannai, H. gigantea, H. fulgens, and H. diversicolor. In H. discus hannai, 83% of the metaphase had 2 pairs of 45S rDNA sites, located at terminal of the long arm ends of chromosomes 13th and 16th, respectively. In H. gigantea, about 75% of the metaphase had 3 pairs of 45S rDNA sites, located at the terminal of the short arm of chromosome 6th, and at the terminal of the long arm of chromosomes 14th and 17th, respectively. In H. fulgens, about 85% of the metaphase cells detected three pairs of 45S rDNA sites, located at the terminal of the long arms of chromosomes 4th, 6th, and 8th. In H. diversicolor, about 65% of the metaphase had 3 pairs of 45S rDNA sites, located at the terminal of the short arms of chromosomes 3th, 4th, and 12th. In addition to the main mode, there were other low-frequency modes in all the 4 species of abalone, suggesting that these abalone may have several unstable 45S rDNA sites besides the unambiguous sites. The number and the location of 45S rDNA loci in abalone showed a high level of intraspecific variation in general. These findings may enrich the cytogenetic research data of abalone and provide basic data for the further studies of genetic breeding in abalone.