| Cyprinus carpio var.qingtianensis has been cultivated for thousands of years and belongs to Cyprinidae fish.Few studies have reported genetic breeding improvement of Cyprinus carpio var.qingtianensis as the experimental object,especially in distant hybridization breeding.Cyprinidae fish is the experimental parent with high appearance rate in distant hybridization breeding,so Cyprinus carpio var.qingtianensis also has the potential for distant hybridization breeding.Hybridization plays an important role in promoting evolutionary radiation and forming new species.According to the distance of the genetic relationship between the female parent fish and the male parent,hybridization can be divided into two categories,one is distance hybridization,which is carried out within species,and the other is close hybridization,which is carried out over species,The two complement each other.The formation of new species mainly depends on the partial recombination of male and female genes,and is caused by adaptive differentiation.The first offspring from distant hybridization are generally not strong enough,usually sterile and easy to die.The separation range of offspring is very large,and it needs to be tracked and cultivated for a long time until there is a stable offspring.Distant hybridization leads to the formation of new species by forming hybrid lines.Through distant hybridization,the excellent traits from different species will be gathered,and the strengths of each family will be gathered,and finally the hybrid offspring with excellent traits will be cultivated and even a new species will be created.In this study,the first generation of hybrid fish was bred by means of distant hybridization with Cyprinus carpio var.qingtianensis as the female parent and blunt-head bream as the male parent.The first generation of hybrid fish was observed and studied in all directions through geometric morphology measurement,chromosome identification,muscle nutrient composition determination,gonad section observation and 5Sr DNA molecular markers.Now geometric morphology analysis has been used as a measuring tool to solve many biological problems,including speciation,species identification,fish-habitat association and hybridization,and to check the shape changes of various organisms.In this study,with reference to the land mark standard of Cyprinidae fish,a total of 71 fish,including Cyprinus carpio var.qingtianensis,blunt-head bream and the first generation of hybrid fish,were measured with geometric morphology of 13 land marks.These three kinds of fish have great differences in morphology.The first principal component(PC=90.226%>90%)can be used to distinguish the female parent,the male parent,and their hybrid offspring.The plot of the first and second main components of the hybrid fish and its two parents shows that the ground mark data of the Cyprinus carpio var.qingtianensis,the blunt-head bream and the hybrid fish are relatively clustered,and the group can be completely distinguished from the group.Moreover,the ground mark data of the hybrid fish and the parent Cyprinus carpio var.qingtianensis are closer to each other,and far from the parent blunt-head bream.The phylogenetic tree of geometric morphology shows that the geometric morphology of the female parent fish and its offspring is more similar,and there are still essential differences with the female parent.In short,it can be concluded from the geometric morphology that the morphological differences between the parent and the hybrid offspring are essentially different.According to the measurement of the muscle of the first generation of hybrid fish,the hybrid fish lacks methionine+cystine(Met+Cys),but is rich in phenylalanine+tyrosine(Phe+Tyr).The ratio of essential amino acids in the muscle protein of hybrid fish to total amino acids is EAA/TAA=39.64%,close to 40%.In addition,the ratio of essential and non-essential amino acids in the protein is EAA/NEAA=83.82%,more than 60%,It conforms to the ideal amino acid model of FAO or WHO,and the quality of this protein is qualified and good.This shows that the protein in the muscle of hybrid fish is good and has high nutritional value.The chromosome identification of the first generation of hybrid fish was carried out.The number of chromosomes was more than 100 and the number of chromosomes was between 110-124.The selection of these chromosomes was carried out according to certain principles.The degree of dispersion of the selection was appropriate.The mitotic metaphase chromosomes with a relatively complete number of chromatids were about 20,and the number of chromosomes in 124 was more than half of the 20,,Therefore,it is speculated that there may be triploid in the hybrid offspring of the field fish Qingtian and the megalobrama bream,but further karyotype verification and flow cytometry verification are needed to obtain accurate results.The results observed from the gonad section of the hybrid fish were that the spermary of the hybrid fish was incompletely developed and was light red,with a small amount of blood vessels in the tissue,and the left and right structures were symmetrical.Through the paraffin section observation,it was found that the majority of sperm cells were in abnormal development state,even degenerated,and only normal mature sperm accounted for a small part.At the same time,there was no sperm outflow from the abdomen of the male fish,so it was speculated that male infertility;The ovarian tissue is relatively plump and light yellow,but the structure is asymmetric and the development is abnormal.Through paraffin section observation,it was found that most of the ovarian cells were in phase II,III and IV,but the ovarian development was abnormal and left and right were asymmetric.It is preliminarily determined that the fertility of the hybrid fish is not high.There are four types of 5Sr DNA of the hybrid fish in this study,of which the shortest 186 bp type is inherited from the male parent blunt-head bream,while the other 201 bp,404 bp and 607 bp are inherited from the female parent Cyprinus carpio var.qingtianensis.In addition,there are four types of 5Sr DNA coding region sequences in the 5Sr DNA sequence of hybrid fish,and they are highly conserved.Each 5Sr DNA CDS sequence has a complete internal transcription control unit,which is the main structure of transcription initiation.There are internal elements IE,Box A and Box C,and these internal transcription control units are basically not mutated and very conservative.Basically,the CDS sequence of the 5Sr DNA of the hybrid fish is consistent with the CDS sequence of the 5Sr DNA of the parent.From here,it can be seen that the CDS sequence of the hybrid fish has good genetic characteristics.In addition,there are basically some base mutations in the NTS segment of the 5Sr DNA.The loss and mutation of these bases show the characteristics of genetic variation,which may be far from the genetic distance of the parent Chromosome incompatibility between different species has a great relationship. |
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