Irradiating red bacteria with ultraviolet light

Many people have heard of hybrid breeding. The hybrid rice developed by Yuan Longping uses the principle of combining genes from different species to produce better genes. Mutation breeding is a breeding method that is exactly the opposite of hybrid breeding. It uses external factors to induce mutations in the species themselves. The use of ultraviolet rays to irradiate red bacterial culture fluid is also a research based on the principle of mutation breeding.

Mutation breeding refers to a breeding method that uses physical and chemical factors to induce mutations in the genetic characteristics of animals and plants, and then selects single plants/individuals that meet certain requirements from the mutant group to cultivate new varieties or germplasm. It is a modern breeding technology developed after selective breeding and hybrid breeding.

In 1927, HJ Mahler of the United States discovered that X-rays can cause heritable mutations in fruit flies. In 1928, LJ Statler of the United States confirmed that X-rays had a mutagenic effect on corn and barley. Subsequently, H. Nilsson-Ehle and A. Gustafsson of Sweden used radiation to obtain barley mutants with practical value in 1930; D. Torunna used X-rays to breed the high-quality tobacco variety "Hlorina" in 1934. In 1942, C. Auerbach discovered that mustard gas could cause various mutations similar to those caused by X-rays, and in 1948 A. Gustafson used mustard gas to induce mutants in barley. After the 1950s, mutation breeding methods were improved and achieved more significant results. For example, the United States used X-ray and neutron mutation to breed Todd's Mitcham, a peppermint variety resistant to wilt disease that had not been successfully bred by hybridization methods. Since the 1970s, mutagenic factors have developed from early X-rays to gamma rays, neutrons, a variety of chemical mutagens and physiologically active substances, and mutagenic methods have developed from single treatments to combined treatments. At the same time, mutagenic breeding has been closely combined with hybrid breeding, tissue culture, etc., which has greatly enhanced the practical significance of mutagenic breeding.

Through the research in recent decades, people's understanding of the principles of mutagenesis has gradually deepened. We know that conventional assisted hybrid breeding is basically the recombination of chromosomes. This technology generally does not cause chromosome mutations and it is even more difficult to touch genes. The effects of radiation are different. Some of them collide with atoms and molecules in cells, causing ionization or excitation; some produce photoelectric absorption or photoelectric effect in the form of energy; and some can cause a series of physical and chemical processes within cells. These will cause varying degrees of damage to cells. It will affect the number and structure of chromosomes, causing some chromosomes to break, some to lose a segment, and some to be connected head to tail in the process of "self-repair" after breaking, or to be "mixed up" and cause chromosome inversion and translocation respectively. Of course, radiation can also act on the base blocks of nucleotide molecules in chromosomes, causing mutations in genes (genetic codes). As for chemical mutagenesis, some agents use their alkyl groups to replace hydrogen atoms in other molecules, while others are analogues of nucleotide bases themselves, which can "pass off as genuine" and cause errors in DNA replication. Undoubtedly, these will cause mutations in the plant's genes. The induction of physical and chemical factors makes the mutation rate of plant cells thousands of times higher than usual, and some mutations are difficult to obtain by other means. Of course, most of the mutations produced cannot be inherited, so the early generations after radiation are generally not in a hurry to be selected.