Autotriploid Origin Of Carassius Auratus As Revealed By Chromosomal Locusanalysis With 5SrDNA Gene And Composition Analysis

Polyploidy is an important method of biological evolution and species occurence,which contian three or more than three sets of the complete genome. In this paper,we discuss the formation mechanism and biological characteristics of the crucian carp and the artificial induced autopolyploid.Specific studies are as follows:1.In the Dongting water system, the crucian carp(Carassius auratus L.) population is characterized by the coexistence of diploids form(2n=100, abbreviated 2nCC) and polyploids form(3n=150, abbreviated 3nCC, 4n=200).We got more particular knowledge of the genetic composition and origin of polyploidy crucian carp by fluorescence in-situ hybridization(FISH) with labeled 5S gene or species-specific centromere probes.Analysis of 5S gene chromosomal locus revealed that the crucian carp with 150 chromosomes(3n=150, abbreviated 3nCC)is of triploid origin.The analysis of species-specific chromosomal centromere locus revealed that 3nCC individuals possess three sets of crucian carp-derived chromosomes. Our results directly proved that crucian carp with 150 chromosomes are of autotriploid origin. This is the first report documenting autopolyploid origin in mixed diploid-polyploidcrucian carp population, and our results contribute to the study of polyploidization and the evolution of vertebrates.2. Allotetraploids of RCC(♀) × BSB(♂) contain two sets of RCC-derived chromosomes and two sets of BSB-derived chromosomes, and would be supposed to produce allodiploid gamete. However, abnormal chromosome behavior during meiosis in allotetraploids may lead to the formation of autotriploid gametes.Following activation by UV-irradiated BSB sperm, the fertilized eggs of tetraploid hybrids(abbreviated as 4nF1)(4n=148, AABB) of Carassius auratus red var.(abbreviated as RCC)(2n=100, AA)( ♀) × Megalobrama amblycephala(abbreviated as BSB)(2n=48, BB)(♂)developed into normal live gynogenetic offspring without chromosome doubling treatment.Some of these were autotriploids with three sets of red crucian carp chromosomes(abbreviated as G1)(3n=150, AAA). G1 were all-females, and can produced unreduced eggs at age 1 year.After activation by UV-irradiated BSB sperm, the fertilized eggs of G1 developed into a second generation of autotriploid gynogenetic offspring(abbreviated as G2)(3n=150) without chromosome doubling treatment.At present, autotriploid gynogenetic offspring has been breeding to the third generation.It could set up a stable autotriploid gynogeneticoffspring cloning system(G1- G3). The autotriploid fish could provide an important source of gametes for the production of all-female triploid fish and for the establishment of autotriploid gynogenetic lines.3. In many species of cultured fish,the triploid and the unisexual offspring had advantages in growth rates and resistibility.This study carried on the comparative study bout morphological traits and growth rates.Additionally,the body color、the ratios of the measurable traits and the countable traits differed significantly between G1 and RCC;the growth rates of G1 and G2were higher, and obviously increased, compared with those of RCC over the entire period. Importantly,autotriploids had obvious genetic variation which could inherit to the offspring. While, autotriploid gynogenetic offspring laid the foundation for the industrialization promotion of aquaculture.