实验动物,遗传定律 z-bo 2020-07-28 667

　　1. Mendelian law of inheritance and its extension

　　Mendel (Mendel, 1865), as an indicator of the hybridization experiment, the color (white and purple) and seed shape of the pea flower (using 7 sets of relative attributes, such as complete circle and contraction). , Got Mendel’s inheritance law. The genetic law of experimental animals still follows this law, but here we take mice as an example.

　　(1) A pair of relative characteristics and the law of separation: mating produces only colored strains of each generation of mice, while albinism (white hair and red eye) mice produce the first parent-child (F1) mouse full color. The colored letters shown in F1 are called dominant traits, and the albino traits lacking F1 are called recessive traits. This is Mendel's law of dominant and recessive (low dominance).

　　Secondly, the colored and self-chemical properties of the second generation (F2) produced by F1 mating account for a certain proportion (321). This is called segregation difference. This phenomenon can be explained by controlling the locus (allele) of the hair. When the gene supporting color is represented by C and the gene determining the albino disease is represented by c, the relationship between the explicit law and the separation law is shown in Figure 34. In the genotype shown in Figure 3-1, the paired genes (C/C or c/c) are called homozygotes, and the different genes (C/c) are called heterozygotes. The P in the figure represents the parent. (2) Two or more pairs of relative traits and the law of free combination: As mentioned above, traits controlled by a pair of dominant and recessive genes are inherited according to the law of segregation. In addition, how to inherit two or more sets of characteristics? During the mating process, the relative characteristics of the two groups of hairy mice (albinism and hairless mice) (Figure 3-2), the F1 of the hairy mouse, and the F2 obtained by crossing each other, have a certain proportion of colored, hairy, Colored, hairless, albino and hairless mice (9232321). At the moment, if you only view

　　color and plaster or hairy round hair, the distance between them is 3:1, therefore, colored and albino properties do not affect the hair and hairless properties, and the hairy and hairless properties do not affect the colored and white hair properties. These alleles are independent of each other and each play its own genetic role, which is called the law of free combination. For completely dominant alleles, if there are n pairs of alleles inherited independently of each other, the theoretical separation ratio of F2 to hybridization is (3 +1) n expansion.

　　(3) Incomplete dominance and commonality: the dominant-recessive relationship between alleles is still unclear, and the heterozygous (Aa) phenotype is between homozygous dominant and homozygous recessive phenotypes. , Different from homozygous dominance. The inheritance of this characteristic is called incomplete dominance, semi-dominated and non-dominated. The W gene (dominant leukoplakia, dominant spot) in mice is equivalent. Miscellaneous (W/+) patches appear on the fur, and homozygous (W/W) fur is white. When different phenotypes have characteristics of both parents, they are called commonality. There is rarely a genetic recessive relationship between the heterologous protein or isoenzyme properties found in the electropherogram of genetic testing and specific immunological properties, and it should be emphasized that they are usually the main ones. Have.

　　(4) Sex-related inheritance: The genetic formula of genes on sex chromosomes is different from that of autosomes. For example, the hairless gene (sperse-

　　FuhSpf), when homozygous hairless female mice are crossed with normal male mice, F1 female mice become normal, while male mice have poor hair. Yes. This is because the hairless gene is on the X chromosome. In F1 female mice, each parent has an X chromosome, so the inherited gene is +/Spf, and its phenotype is normal. However, the chromosome combination of male mice is XY. In other words, male mice inherit only one X chromosome from their parents, and the X chromosome of the Y chromosome does not have the Spf gene, so the genotype is Spf/Y (hemizygous), and its phenotype is poor hair. .. This phenomenon is called sex inheritance. 2. Hardy Weinberg's law bi. In the evolutionary history of biology, the existence of individual organisms is meaningless. Only when these organisms are born in groups can this species exist and develop. I will. The so-called group actually refers to the sum of all members of a group of species, subspecies, variants, strains or other organisms. As we all know, genetic differences between individuals are caused by allelic differences. Populations are composed of groups of individuals who can mate and reproduce. Genetic differences between groups depend on differences in gene frequency.

　　British mathematician Hardy and German doctor Weir1berg published in 1908 the main genetic methods of genes and gene frequencies. This is called the Hardy-Weinberg method, also known as the gene balance method. The main points are as follows. In a lot of

　　(1) In random crosses, in the absence of other factors, the gene frequency does not always change between generations. (2) Regardless of the genotype frequency, as long as one generation of random crosses is carried out, the autosomal genotype frequency of the large population will reach equilibrium. Unless affected by other factors, the next generation of random hybrids will maintain this balance.

　　(3) In a balanced state, the relationship between genotype frequency and gene frequency is: P = P2, Q = Pq, R = q2,

　　These relations can be obtained from the formula and it is not difficult to confirm: (p tens q) 2 = p2 + 2pq tens q2

　　This is the case of allele pairs, and other multiple alleles can be inferred by analogy. The genotype composed of multiple gene pairs cannot be balanced in a single generation random cross. The more sites involved, the more offspring are needed to reach equilibrium. It takes several generations for sex-related genes to gradually reach equilibrium.

　　This is the "preservation method" of population genetics. By analyzing the genetic rules of gene frequency and genotype frequency in each generation of the population, you can understand the genetic structure of the population and keep the genetic specificity of the population relatively stable.

　　(four) gene mutations

　　Each animal gets two sets of genes from its parents. One is from the father and the other is from the mother. Each group has thousands of genes, and these genes are stably passed on to the next generation. However, during its spread, genes may mutate due to errors or mutations. The so-called mutation refers to the change of the long chain base of the DNA molecule, or the mutation of the genetic material at a specific site on the chromosome. Mutations that occur under natural conditions are called spontaneous mutations or mutations. The artificial method is called induced mutation. Mutations are common. In other words, you can mutate genes that affect various characteristics.

　　Variation is reversible. This rule is very important in laboratory zoology. When using mutant animals, if conservation efforts are unsuccessful, breakthrough species may return to wild type.