染色体,基因,性状,实验动物 z-bo 2020-07-28 572

　　1. Chromosomes

　　The filaments in the cell nucleus observed with an optical microscope are called chromosomes. The number and morphology of chromosomes vary from species to species. Genes are arranged on chromosomes. The chromosomes composed of DNA, histones and non-histone proteins are the main components of the cell nucleus. The content of DNA in the nucleus of different organisms varies greatly. The DNA content in the somatic cell nucleus of different tissues of the same organism is the same, but the DNA content in the sex cell nucleus is only half of the DNA content in the somatic cell nucleus. Every cell in an animal has two sets of two identical chromosomes, called diploids. For example, 2n = 40 for mouse somatic cells and n = 20 for sex cells. One set of chromosomes is related to sex, called sex chromosomes, and the other set is called autosomes. Sex chromosomes are chromosomes that determine sex. In mammals, female chromosomes are composed of pairs of chromosomes of the same shape and size or XL. In contrast, male chromosomes are composed of X chromosomes and much smaller Y chromosomes. XY. In birds and lepidopteran insects, the male chromosome is composed of a pair of Z chromosomes (ZZ) of the same shape and size, and the female chromosome is composed of a Z chromosome and another W chromosome (ZW). )composition. 2. Gene Gene is a specific part of DNA molecule on cell chromosome, is the functional unit of DNA molecule, and the basic unit of genetic information transmission. The entire set of DNA of a chromosome is called the genome. In animal somatic cells, only 1% to 2% of genes are active and can transcribe mRNA. These genes exist in a free state, and the remaining genes combine histones into inactive high-order helices. Different cells have different active and inactive gene profiles, which is the basis of cell differentiation.

　　Allele: Genes are arranged in a chromosome super-chain, and each gene has its own locus. Genes occupying the same locus on homologous chromosomes are called alleles. A population locus has more than one genetic variation called multiple alleles. Because many genes have multiple alleles, the variability of biological populations is great. This is very beneficial to the biological society, and diverse individuals can easily adapt to different environmental conditions. For example, the locus that controls immunological characteristics (such as blood type) is multiple alleles.

　　3. Features

　　Characteristics refer to the morphological, physiological, biochemical or psychological characteristics that can be observed in all living things, called Chameters. The different characteristics are the result of the interaction between the gene and the environment that plays a role in the expression process. The coat color is black and brown, hair and no hair, etc. are not continuously changing, but the characteristics that can be clearly distinguished are called qualitative characteristics, and continuous but unclear changes in weight, length, and life are called quantitative characteristics. (Quantitative characteristics). However, the role of each gene is qualitative in nature, so genotype differences should also be qualitative. Quantitative traits are basically the same as qualitative traits. However, since the phenotype of a quantitative trait is a continuous observation value obtained by measurement, each observation value (phenotype) cannot be directly related to the genotype. Therefore, statistical data such as the overall average and standard deviation should be used for analysis when making selections.