Genetic Characterization Of Larimichthys Crocea,Larimichthys Polyactis And Their Hybrids

Larimichthys crocea and Larimichthys polyactis belong to the genus Sciaenidae and the genus Larimichthys.They are important economic fish in the offshore of China and rank among the famous four sea products.In order to better develop and utilize the germplasm resources of L.crocea and L.polyactis,this study studied the chromosomal characteristics of L.crocea and L.polyactis and the genetic characteristics of their distant hybrid progeny.The research results are as follows:1.Using karyotype and banding method,and fluorescence in situ hybridization?FISH?to study the chromosomal characteristics of L.crocea and L.polyactis,and explore the cytogenetic differences between L.crocea and L.polyactis:The karyotype analysis showed that the karyotype of L.polyactis was 2n=6sm+42t,NF=54;the karyotype of L.crocea was 2n=2sm+22st+24t,NF=72,significant differentiation of karyotypes between species;The distribution of heterochromatin regions on chromosomes and the distribution of seven pairs of repetitive DNA sequences(18srDNA,5SrDNA,?CA?₁₅,?GA?₁₅,?CGG?₁₀,Rex6,U2 snRNA)were mapped by C-banding and FISH techniques,respectively.The results showed that the centromere regions of the two fish chromosomes showed similar positive heterochromatin bands,and there were some differences in the distribution patterns of the seven pairs of repetitive DNA sequences on the chromosome.In L.polyactis,18SrDNA and 5S rDNA were located in two pairs.The short arm ends of the centromeric homologous chromosome?sm?,and the location of L.crocea genome on the two pairs of subterminal centromere chromosomes?st?.Overall,the heterochromatin on the chromosome of Larimichthys and the distribution patterns of related repetitive DNA sequences are very similar.2.Comparative analysis of the karyotype and COI gene sequences of the hybrids of L.polyactis???×L.crocea???and their parents showed:The karyotype of the hybrid offspring was 2n=8sm+12st+28t,NF=68.Hybrid offspring and their parents have same chromosome number,but karyotypic variation were observed,which could be attributed to fusion and rearrangement of the parental genome during the hybridization process.At the same time,the homologous sequence of the 672 bp COI gene of the hybrid progeny and their parents was analyzed,which indicated that the sequence of the hybrid progeny was almost identical to that of the L.polyactis.The phylogenetic analysis was analyzed based on Kitumra-2-Parameter-Distance two-parameter model.The genetic distance between hybrid offspring and L.polyactis was 0.011,which was close to the average intraspecific genetic distance within the species.A phylogenetic tree was constructed based on the sequence of the COI gene fragment and showed that the hybrid and L.polyactis were clustered together.Hybrid offspring showed strict maternal inheritance on the mitochondrial COI gene.