What are the genes of life?

Johnson of Denmark first proposed the term "gene" to replace the German biologist Mendel's hereditary factors in 1899. He also pointed out in 1911 that fertilization is not the inheritance of specific traits, but rather a latent ability, which he called a "genotype". Genotypes may or may not exhibit visible traits (expressive) in an individual.

Johnson's term gene has stuck. Later in classical genetics, the meaning of a gene as a genetic unit existing in a cell with the ability to reproduce itself includes three elements: first, it is a functional unit in controlling the development of hereditary traits, so it is also called a cis-transgender; second, it is a unit of mutation in generating variation, so it is also called a mutant; and third, it is a unit of recombination or exchange in heterosis, so it is also called recombinatrix. The division of genes into cis-antigens, mutants and recombinants proves that genes are divisible and breaks the traditional "trinity". This has now been confirmed by modern genetics.

The biologist Müller argued that the founders of the concept of the gene should be freed from the constraints of the gene, and sought to materialize the gene with particles. If the gene was material, he proposed, one could hit it with a free electron or the like and get an estimate of its size. It was under the guidance of this idea that Müller first used X-rays to cause artificial mutations to study the behavior of genes, and in 1921, Müller made it clear that: the gene has a definite position on the chromosome, and it is a tiny particle in itself; its most distinctive feature is its "self-reproducing nature"; and that a newly reproduced gene, after more than one generation, can be "made hereditary". "become inherited"; genes are similar to viruses. Today we know that the simplest virus has more than one gene, and that it has a protein shell. But the fact that he proposed that genes resemble viruses is enough to reflect Müller's attempt to concretize and materialize their causal structure. Because of this, he was convinced that "we can finally grind genes in a mortar and cauterize them in a beaker".

In 1951, American biologist Morgan and others published the book The Mechanism of Mendelian Heredity. This book summarized their main genetic ideas. In this book, Morgan presented a comprehensive theory of genetics.

(1) genes are located on chromosomes; (2) since the number of genes an organism has greatly exceeds the number of chromosomes, a chromosome usually contains many genes;

(3) genes have a certain position and a certain order on chromosomes and are arranged in a straight line;

(4) genes are not permanently linked to each other, and in the course of meiosis They are often exchanged in an orderly manner with alleles on homologous chromosomes;

(5) genes form interlocking clusters on chromosomes, and genes located in different interlocking clusters segregate and recombine freely in the formation of gametes according to Mendel's first law of heredity and Mendel's second law of heredity, and genes located in the same interlocking cluster are interlocked and exchanged according to Morgan's third law of heredity in the formation of gametes. Exchange. Genes are as important to geneticists as atoms and electrons are to chemists and physicists. There is a profound quote from Morgan on this point, and it is said with great verve: "As chemists and physicists assume invisible atoms and electrons, so geneticists assume invisible elements - genes. The main ****similarity between the three is that chemists, physicists and geneticists each draw their own conclusions based on data."

To date, the principle that genes are on chromosomes applies from the highest mammals to the lowest bacteria and viruses, so genetic theory scientifically reflects the laws of inheritance in biology. But gene theory also has limitations; no one knew at the time what kind of substance a gene was; as for what function such a genetic particle actually has, how it functions, and a host of other questions, gene theory did not address them.

Modern biology proves that genes are the carriers of genetic information, and that they are very small segments of DNA (deoxyribonucleic acid) or RNA (ribonucleic acid) molecules in some viruses. A DNA molecule can contain hundreds, thousands, or tens of thousands of genes, each of which contains several pieces of genetic information. All known genetic information is in the form of a triplet code.