A Preliminary Study On The Molecular Cytogenetics Of Four Species Of Abalone

Four species of abalone,including Haliotis discus hannai,H.diversicolor,H.gigantea and H.fulgens,play an important role in Chinese abalone breeding industry,and the demand for seed industry is urgent.However,the basic research of abalone genetics is still lag behind,especially in the molecular cytogenetics level.The research data are restricted to the traditional karyotype analyses and the fragmentary repeat sequence FISH(Fluorescence in situ Hybridization)analyses,which can not meet the needs of the current structural genomics and genetic breeding research.Therefore,this study cloned and analyzed 5S rDNA multiple variants and 18S rDNA fragments of four species of abalone.The 2 rDNAs and 2 microsatellite sequences were located on four species of abalone chromosomes by FISH,and the relative positions between the 2 repeats were analyzed by double-color FISH.The main results are as follows:1.The 5S rDNA of each species of abalone contains two or more types,3 types of H.discus hannai are obtained(441 bp,1130 bp,1658 bp),2 types of H.fulgens are obtained(484 bp,536 bp),2 types of H.gigantean are obtained(318 bp,714 bp),and 4 types of H.diversicolor are obtained(200 bp,404 bp,485 bp,740 bp),respectively.5S rDNA types of H.discus hannai and H.diversicolor have obvious individual differences.The NTSs of four species of abalone have polymorphism in the genome,between individuals and species,showing the characteristics of birth-and-death evolution model and rapid evolution.2.The FISH results of 5S rDNA showed that the three types of 5S rDNA of H.discus hannai were located at the 11 th pairs of chromosomes in the near centromeric region of the long arm,the type II 5S rDNA of H.gigantean was located at the near centromeric region of the short arm of the 4th pairs of chromosomes,and the type I 5S r DNA localization of H.diversicolor was on the long arm near centromere area of the 5th pairs of chromosome.No signal was detected of the other types 5S rDNA of three species of abalone and all types of H.fulgens.3.18S rDNA is highly conserved in four species of abalone,but the number of 18S rDNA sites is generally polymorphic.Statistical results showed that the mode of H.discus hannai is 2 pairs,the mode of H.fulgens,H.gigantean and H.diversicolor were 3 pairs.The 18S rDNA was distributed at the ends of chromosomes of four species of abalone,but there were interspecific differences of their distribution.2 pairs of signals of H.discus hannai located in 13 th,15th pairs of chromosomes,3 pairs of signals of H.fulgens located in 4th,6th,8th pairs of chromosomes,3 pairs of signals of H.gigantean located in 5th,14 th,17th pairs of chromosomes,and 3 pairs of signals of H.diversicolor located on the 3rd,4th,12 th pairs of chromosomes.4.Single or double-color FISH results of microsatellites(CA)n and(CAA)n in four species of abalone showed that(CA)n of Haliotis discus hannai,H.gigantean and H.diversicolor had clusters of signals,and(CAA)n of Haliotis discus hannai,H.fulgens,and H.gigantean had clusters of signals.There were differences of two microsatellites in intraspecific and interspecific.5.Double-color FISH results of four species of abalone repeat sequences showed that 5S rDNA was not collinear with 18S rDNA,and there was little or no two microsatellites distribution on the chromosomes of 18S rDNA.The results provide a basis for the identification and evolution of chromosomes and germplasm identification of four species of abalone,lay a foundation for further research on molecular cytogenetics of abalone.