Summary and classic examples of high school biogenetics (detailed)

DNA is a substance that causes stable genetic changes of R-type bacteria (that is, R-type bacteria are transformed into S-type bacteria), and various characteristics of phage are also passed on to future generations through DNA. These two experiments prove that DNA is genetic material.

> Modern scientific research has proved that genetic material includes RNA as well as DNA. Because the genetic material of most organisms (such as all prokaryotes, eukaryotes and some viruses) is DNA, only a few organisms (such as some viruses) are RNA, so DNA is the main genetic material.

> the diversity of base pair sequences constitutes the diversity of DNA molecules, and the specific base pair sequences constitute the specificity of each DNA molecule, which explains the reasons for biodiversity and specificity from the molecular level.

> the transmission of genetic information is accomplished by the replication of DNA molecules (pay attention to its semi-conservative replication and unwinding replication characteristics).

The unique double helix structure of & gt05DNA molecule provides an accurate template for replication; Through base complementary pairing, replication can be accurately guaranteed.

The descendants of & gt06 are similar to their parents in character, because they have obtained copies of DNA copied by their parents.

> gene 07 is a DNA fragment with genetic effect. Genes are arranged in a straight line on chromosomes, which are the carriers of genes.

The expression of & gt08 gene is realized by DNA controlling the synthesis of protein (that is, the transcription and translation process).

> Because different genes have different sequences of deoxynucleotides (base sequences), different genes contain different genetic information. (that is, the deoxynucleotide sequence of a gene represents genetic information).

>10 The sequence of deoxynucleotides in DNA determines the sequence of ribonucleotides in mRNA, and then determines the sequence of amino acids in protein. The sequence of amino acids ultimately determines the specificity of protein's structure and function, which makes organisms show various genetic characteristics. Therefore, all biological characters are determined by genes and directly reflected by protein molecules.

>11All genetic traits of organisms are controlled by genes. Some genes control the metabolic process by controlling the synthesis of enzymes; Another situation in which genes control traits is to directly affect traits by controlling the structure of protein molecules.

>12 gene segregation phenomenon: when two homozygous parents with a pair of relative traits cross, the first generation only shows dominant traits; In the second generation, the phenomenon of character separation appeared, and the quantitative ratio of dominant characters to recessive characters was close to 3: 1.

The essence of> 13 gene segregation is that alleles located on a pair of homologous chromosomes in heterozygote cells have certain independence. When an organism undergoes meiosis to form a gamete, alleles will separate with the separation of homologous chromosomes, enter two gametes respectively, and be passed on to the offspring independently with the gametes.

> genotype 14 is the internal factor of trait expression, while phenotype is the expression form of genotype.

The essence of the law of free combination of> 15 genes is that the separation or combination of non-allelic genes located on non-homologous chromosomes does not interfere with each other. In the process of meiosis to form gametes, alleles on homologous chromosomes are separated from each other, and non-alleles on non-homologous chromosomes are freely combined.

>16 There are two main ways to determine the sex of organisms: one is XY type (that is, males have a pair of heteromorphic chromosomes XY, females have a pair of homomorphic chromosomes XX, and the sex of offspring is determined by males), and the other is ZW type (that is, males have a pair of homomorphic chromosomes ZZ, females have a pair of heteromorphic chromosomes ZW, and the sex of offspring is determined by females).

The heritable variation of> 17 comes from three sources: gene mutation, gene recombination and chromosome variation.

>18 gene mutation is of great significance in biological evolution. It is the fundamental source of biological variation and provides the initial raw materials for biological evolution.

There are two ways to recombine & gt 19 gene: one is that nonallelic genes on non-homologous chromosomes are freely combined in the late stage of the first meiosis; Second, during the first meiosis, non-sister chromatids in homologous chromosomes are cross-exchanged. So usually only sexual reproduction has the process of gene recombination. The gene recombination of bacteria and other general asexual organisms can only be achieved through genetic engineering.

> The genetic recombination of sexual reproduction provides an extremely rich source of biological variation. This is one of the important reasons for the formation of biodiversity and is of great significance to biological evolution.