Early speculation about genetic material Scientists have been speculating about the basis of genetic material for a long time. 1864, the British philosopher Spencer proposed "physiological unit"; 1868, which Darwin called "micro-bud"; 1884, Swiss botanist von Naegeli called it "ectopic"; In 1889, Dutch scholar Defrees called it "the son of the universe". 1883, weismann called it "germplasm", and pointed out that chromosomes in germ cells are germplasm. He thought that germplasm is hereditary, but physique is not hereditary. Germplasm affects physique, but physique does not affect germplasm. This paves the way for rediscovering and widely accepting Mendel's genetic law in theory. [Editor] The concept of "gene" was put forward. The founder of genetics, Austrian Gregor Johann Mendel (1822 ~ 1884), was in Brno.

After eight years' sweat in the garden of Augustine Monastery in Bruen, Czech Republic, he reported his research results of plant hybridization 1865 at the meeting of Austrian Natural Science Society in February. In the second year, he published a famous paper "Plant Hybridization Experiment" in the annual journal of Austrian Natural Science Society, and discovered two basic laws of genetics-separation phenomenon and the law of free combination. This paper points out that every biological character is transmitted through genetic factors, and genetic factors are some genetic units. In this way, the observable genetic trait is distinguished from the inherent genetic factor that controls it, and the genetic factor is born as the embryonic period of the gene. The existence of genes was first inferred by him in19th century, not the result of observation. Shortly after Darwin published his theory of evolution, he tried to explain it by experimenting with peas. But it was not until the end of 19 that people began to pay attention to his research. Although Mendel did not know how this substance existed or what its structure was, Mendel's "genetic factor" laid the foundation for the emergence of modern gene concepts. It can be said that genetic factors are actually what Mendel hypothesized according to his experimental results. Since then, geneticists have embarked on a difficult journey to find genetic entities. In 1903, Sutton (W.S. Sutton 1877 ~ 19 16) and Boveri (Tyrannosaurus Boveri1862 ~19/kloc- They put forward the Sutton-Boveri hypothesis, which holds that genetic factors are located on chromosomes. According to their own research, they believe that Mendel's genetic factors are parallel to the chromosome transmission behavior in the process of gamete formation and fertilization, and put forward the theory of genetic chromosomes, which holds that Mendel's genetic factors are located on chromosomes, that is, they realize that chromosomes are the carriers of genetic materials and link genetic materials with chromosomes for the first time. This hypothesis can well explain Mendel's two laws, which was also confirmed in later scientific experiments. 1909, the Danish geneticist Zhan Sen (W. Johan 1859 ~ 1927) put forward the concept of "gene" in his book Principles of Accurate Genetics to replace the "genetic factor" assumed by Mendel. Since then, the word "gene" has been accompanied by the development of genetics. The word gene comes from Greek and means "life". Zhan Sen also put forward two terms "genotype" and "phenotype" with different meanings, and preliminarily clarified the relationship between genes and traits. However, the gene at this time is still an unproven concept, which is only derived from logical reasoning. [Editor] Exploration of Gene Structure and Function Since Mendel's Law was rediscovered in 1900, the problem of how genes control traits has aroused great interest of many geneticists. Through their unremitting efforts, a number of important achievements have been made. American experimental embryologist and geneticist Thomas Hunter Mann (1866 ~ 1945) and his students began to do a lot of painstaking research on Drosophila around 1908. 19 10 years, he discovered the phenomenon of sex-linked inheritance through the genetic experiment of wink mutation in Drosophila, and revealed the clear connection between one or more genetic characteristics and a specific chromosome for the first time. Through a large number of fruit fly hybridization experiments, he and his colleagues further discovered the third basic law of genetics-the law of chain exchange, thus inheriting and developing Mendel's genetic theory. They finally provided more sufficient, direct and reliable evidence for the theory of genetic chromosomes, and believed that chromosomes were the material basis of the inheritance mode of genetic traits. 1926, his magnum opus "Gene Theory" was published, which established a famous gene theory. He also drew the famous gene mapping map of Drosophila, and completed the description of the latest gene concept at that time for the first time, that is, the genes were arranged in a straight line, which determined a specific trait and could be mutated and exchanged with the exchange of homologous fragments of chromosomes. It is not only a functional unit that determines traits, but also a mutant unit and an exchange unit. Morgan and others also believe that genes are genetic functional units and can produce specific phenotypic effects; Gene is a new structural unit. Gene exchange can occur between homologous chromosomes, but the exchange can only occur between genes rather than within genes; Genes can be mutated from one allele form to another, so genes are mutant units. This is the so-called trinity gene concept of "function, exchange and mutation" which was popular before the 1940s. This understanding links genes with chromosomes and explains the materiality of genes, the place where genes exist and the way they are arranged. Gene is no longer an abstract concept. Of course, people still don't understand the chemical nature of genes and how genes control biological characteristics. Since the 1940s, people began to pay attention to the relationship between genes and traits, that is, to study how genes control traits. 194 1 year, Bedell and Tatum used Streptomyces rubrus as materials for biochemical genetic research. They obtained a large number of auxotrophic mutants of amino acids and vitamins by mutagenesis. These mutant genes cannot produce enzymes, or can only produce defective enzymes. For example, a mutant cannot synthesize tryptophan because it cannot produce tryptophan synthase. Therefore, the researchers put forward the hypothesis of "one gene, one enzyme", which holds that the control of genes on traits is realized by controlling the synthesis of enzymes. This assumption was fully verified in the 1950s. Later, it was found that some protein are composed of more than one peptide chain, such as hemoglobin and insulin, and different peptide chains are encoded by different genes, so 194 1 year Bedell (G.W. Beadle1903 ~) and Tatum (E.L. Tatum/kloc-) The hypothesis of "one gene and one polypeptide chain" was put forward. The theories of "one gene, one enzyme" and "one gene, one polypeptide chain" have greatly promoted the development of molecular genetics, and people are eager to understand the chemical structure of genes. 1949, Pauling (L.C. Pauling1901994) and his collaborators came to the conclusion that genes determine the amino acid sequence of polypeptide chains when studying sickle cell anemia, which changed the principle that genes control metabolism to determine traits from the late 1940s to the early 1950s. Although DNA was found in the nucleus a long time ago, the decisive experiment to prove that it is genetic material was the pneumococcal transformation experiment conducted in Avery (O.T. Avery1877 ~1955) in 1944. He and Macatee (M. McCarty1911~) and others published an important paper on "transformation factors", which clearly confirmed that DNA was the carrier of genetic information for the first time through experiments. 1952 hershey and Chase (M.M. Chase1927 ~) further proved that the genetic material is DNA, not protein. This experiment not only proves that DNA is genetic material, but also reveals the chemical nature of genetic material, which also greatly promotes the study of nucleic acid. 1953, American molecular biologist james watson and British physicist Francis Harry Compton Crick made a study based on m Wilkins and rosalind franklin 1920- 1958! X-ray diffraction analysis, the famous DNA double helix structure model is put forward, which further shows that the gene component is DNA and controls protein synthesis. Further research proves that a gene is a fragment of a DNA molecule. Each gene consists of hundreds of deoxynucleotides, and a DNA molecule can contain several or even thousands of genes. The determination of the chemical essence and molecular structure of genes is of epoch-making significance, which lays a foundation for the study of gene replication, transcription, expression and regulation and opens up a new era of molecular genetics.

Mitochondria in cells are composed of genes.

Gene defect is caused by gene mutation.

The increase or decrease of the number of mitochondria in cells can also lead to genetic defects.

take for example

People with Down syndrome

There is also an additional cell line, 2 1 pair.

The formation of mutation is mainly influenced by environmental factors: 1. Ultraviolet rays from the sun [UV 200-300 nm] 2. Radiation at other frequencies, including x-rays and gamma rays. Hydrolysis and pyrolysis 4. Some plant toxins. Man-made variation substances, such as some hydrocarbons produced by smoking. Before cell division in tumor chemotherapy and radiotherapy, the replication of damaged DNA will cause the relative site combination of wrong base and damaged base. After the daughter cell inherited the wrong base, it also became a mutant cell (a mutant cell), and there was no way out (except through rare reversion mutation and genetic modification).

Reference: There is nothing wrong.

Common sense.