Study On Heterosis Of Cyprinus Carpio Var.jian And Cyprinus Carpio Haematopterus Teminck Et Schlegel And Related Molecular Biology

At present, hybridization is an effective method for developing a fine breed. Economical hybridization (i. e. utilization of heterosis) had been taken as main approach in breeding work conducted in China and abroad. Jian carp(Cyprinus Carpio Var. jian) was the first artificially developed fine breed of common carp with stabilized genetic attributes in China. 30% higher production could be obtained under the same culture method compared with other common carp varieties. Jian carp had been disseminated in large scale for more than a decade, there was a great need to maintain and enhance its fine production related traits through continuous selection and genetic improvement. Huanghe carp(Cyprinus carpio haematopterus Teminck et Schlegel) was a remarkable variety of common carp in northern China, which possessed fine traits such as good meat quality, strong cold resistance and high efficiency of food conversion. In order to provide theoretical guidance for improvement of Jian carp and development of new carp species, self-cross of Jian carp and direct and reciprocal cross between Jian carp and Huanghe carp were conducted. Heterosis of offspring and related molecular biology were compared and studied. This thesis study covered the following aspects: growth comparison, path analysis of growth traits and genetic variation analysis of genome DNA of offspring.1. Growth comparisonGrowth rates of offspring from different crosses were compared through communal rearing test with PIT tagged individuals. Comparison of growth performance was conducted for Jian carp and F₁ hybrids of Jian carp and Huanghe carp. The results showed the growth rate of body weight before the age of 157 d and 398 d of different crosses were HJ(Huanghe carp♀×Jian carp♂)＞JH(Jian carp♀×Huanghe carp♂)＞JL(Jian carp♀×Jian carp♂). Both male and female fishes showed the same results during this period. At the age of 598 d, absolute growth rate of body weight of different crosses were respectively JL＞JH＞HJ, JL(♀)＞JH(♀)＞HJ(♀), JH(♂)＞JL(♂)＞HJ(♂) and the superiority of JL in growth contributed mainly by the female carps was the highest among the offspring. The growth difference between female carps and male ones were significantly different. JH(♀) and HJ(♀) showed the heterosis throughout the cultivation period, while heterosis was maintained only before the age of 157 d in JH(♂) and HJ(♂). So heterosis of JH and HJ was mainly observed before the age of 398 d and it was largely contributed by female individuals.The fullness of individuals in the populations increased along with age. JL showed highest degree of fullnesss over other F₁ hybrids throughout the experiment period. At the age of 157 d and 398 d, the degree of fullness of different crosses was JL＞HJ＞JH. At the age of 598 d, it was JL＞JH＞HJ. JL maintained the highest fullness in both male and female individuals too.Variation coefficient of body length and body weight of different crosses was HJ＞JH＞JL at the age of 157 d and 398 d and HJ＞JH＞JL at the age of 598 d. The result also showed that variation coefficient of boby length was smaller than that of body weight. The growth index had the trend to increase with the age of fishes. HJ had the highest growth index at the age of 398 d and 598 d. In the experiment, the female individuals always showed higher growth index than the male ones.2. Path analysis on growth traitsCorrelation coefficients of body length to body weight and body height to body weight declined with age of fishes. Path analysis revealed that determination coefficient of body length to body weight was higher than that of body height to body weight in JL and HJ at the age of 398 d, which suggested body length was a dominant trait. Body height became the dominant trait for JL and HJ at the age of 598 d. Determination coefficient of body length to body weight was higher than that of body height to body weight in JH throughout the experiment period.At the age of 398 d, determination coefficient of body length to body weight was higher than that of body height to body weight which revealed that body length was the dominant trait for both male and female individuals in all crosses. At the age of 598 d, the dominant traits were respectively body height for HJ(♀) and JL(♀) and body length for JL(♂), HJ(♂)and JH(♀). In the case of JH(♂), the determination coefficients of body length, body height to body weight were almost the same. The determination coefficient of body length and body height to body weight was the important factor to the difference of heterosis among offspring.3. Genetic variation analysis on the genome DNA40 random primers were used to conduct random amplified polymorphic DNA (RAPD) analyse for the genome DNA of Jian carp, Huanghe carp and their F₁ hybrids. The results showed that 155 bands were produced with 33 selected primers, 105 bands of which were polymorphic. Different amplification bands were produced by primer S18, S472, S478(1600bp, 300bp and 950bp in size, respectively) in Jian carp and Huanghe carp, which could be used as molecular genetic markers to differentiate Jian carp from Huanghe carp.For Jian carp, Huanghe carp, direct cross F₁(JH) and reciprocal cross F₁(HJ), the proportions of polymorphic loci were respectively 37.33%, 42.38%, 47.33% and 33.33% and genetic similarity indices were respectively 0.8240, 0.7921, 0.7920 and 0.8569. The order of gene diversity index and Shannon index were JH＞Huanghe carp＞Jian carp＞HJ. Huanghe carp and JH maintained higher degree of intrapopulation genetic variation, while HJ had the smallest degree of genetic variation. The inter-specific genetic distances was respectively 0.2233(JH to Jian carp), 0.2436(JH to Huanghe carp); 0.1749(HJ to Jian carp), 0.2026(HJ to Huanghe carp). The data revealed that F₁ hybrid inherited more genetic material from Jian carp than from Huanghe carp.Four variation types were shown by the RAPD maps. If these variations on genome DNA were associated with some economical traits, the differences on DNA sequences were the basis for heterosis production and its intensity vairation. In this experiment, heterosis was correlated with growth stage. Possible reasons that influenced heterosis were analyzed and some theoretical guidance to aquaculture were provided.