What are the disadvantages of traditional cross breeding and mutation breeding?

Disadvantages of hybrid breeding: it takes a long time and needs to find good characters in time. Disadvantages of mutation breeding: less favorable variation and need to deal with a large number of materials; The direction and nature of the mutation are uncontrollable. The improvement effect of quantitative traits is poor. Related connection: The breeding techniques and methods involved in high school biology include: transgenic breeding, cell engineering, (sexual) hybrid breeding, haploid breeding, polyploid breeding and mutation breeding. These aquaculture knowledge are distributed in all chapters of the textbook, and the content is relatively simple. In the general review of college entrance examination, it is necessary to summarize and expand in breadth and depth to make it a breeding knowledge system, so as to systematically grasp the principles, methods, advantages and disadvantages of biological breeding and achieve the purpose of flexible application. First, the principle of transgenic breeding: gene recombination (or heterologous DNA recombination). Methods: The target gene was extracted → loaded into vector → introduced into recipient cells → gene expression → screened out new varieties that met the requirements. Advantages: it is not limited by species and can be carried out purposefully according to human needs. Disadvantages: it may cause ecological crisis and is technically difficult. 2. Cell engineering breeding principle: cell totipotency method: (1) Plant: cell wall removal → cell fusion → tissue culture (2) Animal cloning: nuclear transfer → embryo transfer Advantages: It can overcome the incompatibility of distant hybridization and cultivate excellent varieties purposefully. Animal somatic cell cloning can be used to preserve endangered species, maintain excellent varieties, save endangered animals, and use the same genetic background of cloned animals for biomedical research. Disadvantages: the technology is complex and difficult; It will challenge biodiversity. Sexual reproduction is an important basis for the formation of biodiversity, and "cloning animals" will lead to the reduction of biological strains and the decline of individual viability. 3. Haploid breeding principle: chromosome variation, tissue culture method: selecting parents → sexual hybridization → pollen produced by F1is cultured in vitro to obtain haploid plants → inducing chromosome doubling to obtain fertile homozygotes → selecting required types. Advantages: obviously shortening the breeding cycle and accelerating the breeding process. Disadvantages: the technology is complex, which needs to be combined with cross breeding and is mostly limited to plants. 4. Polyploid breeding principle: chromosome doubling (chromosome variation) method: colchicine treatment of germinated seeds or seedlings. It can be divided into autopolyploid breeding and allopolyploid breeding. Advantages: it can cultivate new varieties that are not found in nature, and the cultivated plant organs are large, with high yield and rich nutrition. Disadvantages: only suitable for plants, low seed setting rate. 5. The principle of sexual hybridization breeding: gene recombination. Methods: Crossbreeding → Self-crossing → Selection Advantages: Excellent traits in two organisms can be integrated according to human foresight. Disadvantages: it takes a long time and needs to find a good role in time. 6. Mutation breeding principle: gene mutation methods: radiation mutation, laser and chemical substance mutation, space (radiation, weightlessness) mutation → new variety breeding advantages: it can increase mutation frequency, speed up the breeding process, and greatly improve some characters; The range of change is very large. Disadvantages: there are few favorable changes, and a lot of materials must be processed; The direction and nature of the mutation are uncontrollable. The improvement effect of quantitative traits is poor. References: Classification of Biological Breeding Problems