The determination of gene essence has opened the prelude to the development of molecular genetics. From 65438 to 0955, American molecular biologist Benzer made an in-depth study of E.coli T4 phage, revealed the fine structure inside the gene, and put forward the concept of cistron. Benze called the genetic functional unit found by cis-trans experiment cis-trans, and 1 cis-trans determined a polypeptide chain, and cis-trans was a gene. There are many mutation sites in 1 cis-cis-trans-mutant, which is the smallest unit that can produce mutant phenotype after change. There are many recombinants in 1 cis-trans. Recombinants are basic units that cannot be separated by recombination. Theoretically, the change of each nucleotide pair will lead to a mutation, and every two nucleotide pairs can be interchanged. In this way, there are as many mutants and recombinants as there are nucleotide pairs in a gene, and mutants are equal to recombinants. This theory breaks the previous view that genes are the trinity of mutation, recombination and genetic traits, and holds that genes are the smallest indivisible genetic units, so that genes are a nucleotide sequence on DNA molecules and are responsible for the transmission of genetic information. A gene can still be divided into several small units to work, that is, cis-trans, mutation and recombination. One factor usually determines the synthesis of a polypeptide chain, and a gene contains one or several factors. Mutant refers to the smallest mutant unit in a gene, while recombinant is the smallest recombinant unit, containing only a pair of nucleotides. These are all major breakthroughs in the concept of genes. After the nature of gene is determined, people turn their attention to the process of gene transmitting genetic information. In the early 1950s, people knew that there seemed to be a corresponding relationship between genes and protein, but the key problem of gene function, that is, how to transmit the information in genes to protein, was solved in the 1960s and 1970s. From 196 1, nirenberg and Colana gradually realized that nucleotide triplets are a set of encoded amino acids. In 1967, all 64 genetic codes were decoded, thus linking the nucleic acid codes with protein synthesis. Then, the "central rule" put forward by Watson and Crick reveals the basic process of life activities more clearly. 1970, Teming further developed and perfected the "central rule" with the discovery of reverse transcriptase in Routh sarcoma virus. So far, the process of gene information transmission has been clearly displayed in front of people. In the past, people's understanding of gene function was relatively simple, that is, it was used as a template for protein synthesis.

196 1 year, the research results of French Jacob and Mono have greatly expanded people's horizons about gene function. They found that some genes do not synthesize protein template, but only regulate or manipulate, and put forward the operon theory. From then on, genes are divided into structural genes, regulatory genes and manipulation genes according to their functions. Structural genes and regulatory genes: According to operon theory, not all genes can encode peptide chains. Therefore, genes that can encode polypeptide chains are called structural genes, including genes encoding structural proteins and enzyme proteins, and regulatory genes encoding repressors or activators. Some genes can only be transcribed but not translated, such as tRNA gene and rRNA gene. There are also some DNA fragments that do not transcribe themselves, but control the transcription of adjacent structural genes, which are called promoter genes and operon genes. Promoter gene, operon gene and a series of structural genes under their control form a functional unit called operon. As far as their functions are concerned, regulatory genes, manipulation genes and promoter genes all belong to regulatory genes. The discovery of these genes has greatly broadened people's understanding of gene functions and their relationships. Broken genes: In the mid-1970s, French biochemists Xia Mobang and Berger discovered that the structural genes in a cell are not all composed of coding sequences, but non-coding base sequences are inserted in the middle of the coding sequences, which are called spacer regions or broken genes. This discovery was confirmed in 1977 by Chavries in Britain and Franwell in the Netherlands, when they studied the structure of rabbit β-globulin. 1978, biochemist walter gilbert put forward the viewpoint that genes are transcription units. He believes that a gene is a chimera of a DNA sequence and contains two fragments at the same time: one fragment will be expressed and exist in mature mRNA, called "exon"; Although a fragment is also expressed at the same time, it will be deleted in mature mRNA, which is called "intron". In recent years, it has been found that the gene sequence of prokaryotes is generally continuous, and there is almost no "intron" inside a gene, while the genes of eukaryotes are mostly broken genes composed of discontinuous DNA sequences. The expression process of the broken gene is as follows: the whole gene is transcribed from DNA into information RNA precursor mRNA, and the contained sequence will be excised by RNA/ protein complex called "splice", and the two ends will be connected with each other to form a continuous nucleic acid sequence, thus forming a mature mRNA. The existence of DNA molecular breakage gene endows gene function with greater potential. Gene overlap: For a long time, people thought that it was impossible to have overlapping reading structures in the same DNA sequence. However, in 1977, when Weiner studied the gene structure of Q0 virus, he first discovered the phenomenon of gene overlap. 1978, when Feir and Sangor studied and analyzed the nucleotide sequence of Φ x174 phage, they also found that several of the 10 genes contained in the 5375-nucleotide single-stranded DNA overlapped in different degrees, but these overlapped genes had different reading frames. Overlapping genes were found in bacteriophages G4, MS2 and SV40. The overlapping of genes makes the limited DNA sequence contain more genetic information, which is the economic and reasonable utilization of its genetic material by organisms. Pseudogene: 1977, G Jacp put forward the concept of pseudogene after studying the African claw-supporting 5SrRNA gene cluster. It is an inactivated gene whose nucleotide sequence is basically the same as its corresponding normal functional gene, but it cannot synthesize functional protein. The discovery of pseudogenes is the result of eukaryotic application of recombinant DNA technology and sequence analysis. Pseudogenes are found in most eukaryotes, such as Hb pseudogene, interferon, histone, α globulin and β globulin, actin and human rRNA and tRNA genes all contain pseudogenes. Because pseudogenes don't work or can't work effectively, some people think that pseudogenes are equivalent to human micro-organs or as complementary genes. Mobile gene: 1950, American geneticist mcclintock first discovered the mobile gene in the maize genome. She found that there is a control gene called Ds on the maize chromosome, which will change the position, and at the same time cause chromosome breakage, which will inactivate or restore the stability of the genes adjacent to its leaving or inserting position, thus leading to the change of maize grain characteristics. This research did not attract attention at that time. In the late 1960s, British biochemist Shapiro and former West German biochemist Sitter discovered a kind of genetic factor with movable position called insertion sequence in bacteria, and in the early 1970s, some bacterial plasmid resistance and movable genes were discovered. By the 1980s, there were at least 20 such genes. Before the 1990s, scientists finally proved mcclintock's point of view through experiments. Movable genes can move not only within individual genomes, but also between individuals and even between species. As we all know, mobile genes are ubiquitous in eukaryotic cells. The discovery of gene mobility not only breaks the theory of genetic DNA constancy, but also provides new enlightenment and clues for understanding the formation and expression of tumor genes and the information expansion in biological evolution.