What are the advantages and disadvantages of the six breeding methods?

The six breeding methods include four kinds of plants (cross-breeding, distant hybridization, mutation breeding, molecular breeding) and two kinds of animals (cross-breeding, genetic engineering breeding).

First, cross-breeding:

1, the principle: genetic recombination, through the recombination of genes to produce new genotypes, thus producing new excellent traits.

2, the process:

2.1 Preparation before hybridization should first be familiar with the reproductive habits of various fish;

2.2 Selection of appropriate fertilization methods for hybridization hybridization pre-crossbreeding in the approaching sexual maturity and the arrival of the reproductive season, it is important to keep male and female two kinds of fish in separate pools, to avoid the self *** mating;

2.3 Documentation, Listing and management of crossbreeding with different varieties (or species) of fish;

2.4 Accelerating the breeding process from crossbreeding to new varieties of fish breeding and promotion;

2.5 Selection of crossbreeding progeny using the individual selection method, the selection of the general start from the second generation of the child, the factor of the second generation of the greatest range of variation, from which it is hoped to select the desirable variants.

3. Advantage: two or more excellent traits can be concentrated together.

4. Disadvantages: no new genes will be produced, and the offspring of hybridization will have trait separation, breeding process is slow and complicated.

Two: distant hybridization

1, principle: genetic recombination, through genetic recombination to produce new genotypes, thus producing new good traits.

2. Advantages and disadvantages: It can combine the features and characteristics of different species and genera, break through the species boundaries, expand genetic variation, and thus create new types of variation or new species.

The offspring produced are distant hybrids.

Distant hybridization is also an important experimental tool for the study of biological evolution because it tends to reenact the evolution of a species.

Distant hybrids are generally less likely to bear fruit, and even if they do, the hybrids are usually sterile or die young, and the hybrid offspring are separated by a large margin, and the separation of generations is long and not easy to stabilize.

Three: mutation breeding

1, the principle: in man-made conditions, the use of physical, chemical and other factors, induced organisms to produce mutations, from which the selection, cultivated into new varieties of plants, animals and microorganisms.

2. Advantages and disadvantages: the main problem of mutation breeding is that the frequency of beneficial mutations is still low, and it is difficult to control the direction and nature of the mutation.

Therefore, to improve the efficiency of mutagenesis, rapid identification and screening of mutants as well as to explore the pathway of directional mutagenesis, is an important issue in the current research.

Four: molecular breeding

1, principle: the application of genetic engineering in breeding work, through the introduction of genes, so as to cultivate a certain requirement of new varieties of breeding methods.

2. Advantages and disadvantages: the traditional breeding methods are hybridization, the improvement of varieties is mainly subject to the limitations of the variation of the original species, and hybridization between different species (species) is quite difficult, breeding results are difficult to have a big breakthrough, the "green revolution" (green revolution) is very difficult to happen again.

The use of genetic engineering technology for crop variety improvement refers to the use of genetic engineering (geic engineering) technology to introduce specific genes or traits into a target crop that lacks such genes or traits; therefore, the use of genetic engineering technology for crop variety improvement can break through the limitations of the original species and the bottleneck of interspecies hybridization to create new traits or varieties. Therefore, using genetic engineering technology to improve crop varieties can break through the limitations of germplasm and the bottleneck of interspecific hybridization, and create new traits or new varieties, which means that the future "gene revolution" is likely to rapidly replace the "green revolution".

V. Genetic engineering breeding

1. Principle: genetic recombination (or heterologous DNA recombination).

2. Advantages and disadvantages: not subject to species restrictions, can be carried out purposefully according to human needs.

May cause ecological crisis, technical difficulties.