BREEDING BASED ON THE GENETIC RECOMBINATION PRINCIPLE Taryono Faculty of Agriculture Gadjah Mada University

Hybridization It is a combining in the future strains the useful traits and characters inherent in each parent separately it has become the predominant method of improvement of cultivated strains due to hybrid vigor It is known as combination breeding Distinction is made between intra- and interspecific crossing The successful of hybridization is to great extent dependent on the selection of parental materials and how well the breeder is familiar with the genetic processes occurring in the segregating progenies of hybrid populations The choice of parents might seem the best starting point, but in practice, it is better to expound crossing and selection schemes first and then to consider the source and choice of parents in the wider context of breeding strategy

Hybridization The material resulting from hybridization is used in different ways for selection in the breeding of selection strains (open pollinated strains) directly in the production as first generation hybrids (hybrid strains) The improvement of cross pollinated organisms cannot be based on isolation of homozygous genotypes As a consequence of outbreeding, any strain of outbreeding organism has heterogenous genotypes, each being to some extent different from the other ones in a given population Induced selfing of outbreeding organisms leads to inbreeding depression of the offspring

Hybridization Sexual recombination in fish might occasionally happen in nature, but most were conducted artificially The principle of artificial sexual recombination is to impose the male and female gametes of different fishes to fuse together as a zygote by artificial methods that does not happen in natural conditions Those hybrid zygotes will develop into hybrids with some improved characteristics The modified phenotypes appeared in those hybrids is the result of “hybridity expression” of the newly reconstructed genomes of the individuals Sexual recombination is very useful for producing better F1 hybrids

Hybridization Sexual recombination only generally can be done between taxonomically closely related species In fish, sexual recombination not only can be successfully made among closely related species, but also can be applied to those fish species which belong to rather distantly related species Inter-genus sexual hybridization Cyprinus carpio x Carassius auratus Inter-subfamily sexual hybridization Ctenophry idellus (sub-fam. Leucinae) x Megalobrama amblycephala (Sub-fam. Abramidinae) Inter-order combination Carassius auratus (order Cypriniformes) x Oreochromis nilotica (order Perciformis)

Natural barrier in distance recombination The failure of foreign sperm to penetrate the egg Foreign sperm can enter the eggs but it will be degenerated and disappear in the egg cytoplasm without performing any vital function Foreign sperm can enter the egg and enlarge as a male pronucleus but it can not fuse with the egg to form a zygote nucleus Foreign sperm can enter the egg and enlarge as a male pronucleus but it can fuse with the egg to form a zygote nucleus and divide in coordinating with egg cytoplasmic division, however due to unknown natural incompatibility which existed between the sperm and egg, the hybrid zygote nucleus will become heteroploid. The embryo develops abnormally

Open pollinated populations (OPP) The improvement of OPP depends essentially upon the changing gene frequencies towards fixation of favorable allele while maintaining a high degree of heterozygosity Uniformity is impossible and trueness to type is a statistically feature of the population as a whole, not a characteristic of individual plant Two types Population improvement a population is changed by the chosen selection procedures based on purely phenotypic selection (mass selection) 2. Synthetic population improvement which has to be reconstructed from parental lines. t can be constructed from combining inbred, clones as a parent

Heterosis It implies increased vigor of the first generation hybrids as compared to the parental forms It manifests itself fully in the first generation, whereas in the subsequent generation the hybrid vigour goes down substantially Heterotic hybrid seed can be sown commercially once Practical utilization of heterosis involves annual crossing to produce heterotic hybrid seed

Nuclear transplantation It is a diploid nucleus into enucleated egg. It is to combine the nucleus and cytoplasm of different species to produce nucleo-cytoplasmic hybrids Inter-genus combination Nucleus of common carp and cytoplasm from crusian carp. Adult fish with essentials of common carp phenotype and cytoplasmic influenced character at morphological, physiological and biochemical levels were obtained. Both male and female hybrids are fertile 2. Inter –subfamily combination Nucleus from grass carp and cytoplasm of blunt snout bream. Adult fishes were obtained.