What is a chromosome? Better bring some.

Filamentous or rod-like substance in the nucleus, which consists of DNA, protein and a small amount of RNA, is easily stained by alkaline dyes. 1888, Wald first put forward the term chromosome. Chromosome is the most important genetic structure in cells. The study of chromosome structure and function has always been an important topic in cytology and genetics. Chromosomes can be stained with hematoxylin, saffron, crystal violet, Giemsa, fuchsin acetate, lichen red and folgen dyes. In the metaphase of cell division, chromosomes consist of two sister chromatids, which are connected only at the centromere. Each chromatid is coiled by a staining line of DNA molecules. The centromere at the junction of two chromatids is called the initial constriction. Centromere is an important part of chromosome, and its position on different chromosomes is determined. According to the different centromere positions, chromosomes can be divided into four types: metacentric chromosomes, metacentric chromosomes, proximal centromere chromosomes and telocentric chromosomes. Centromeres play an important role in cell division and chromosome migration to the poles. There is also a constriction region related to nucleolar formation on the chromosome, which is called secondary constriction. The size of some chromosomes can be greatly determined by different organisms or different tissues of the same individual and different external conditions of the same organization. The variation range of chromosome length is 0.2 ~ 50 microns and the diameter is 0.2 ~ 2 microns. The chromosome number of each organism is relatively fixed. In somatic cells, chromosomes exist in pairs, while in gamete cells, the number of chromosomes is half that of somatic cells. The number and origin of chromosomes can be regarded as one of the characteristics of living species, so chromosomes can be used as indicators to classify species and explore the genetic relationship between species. Under some physiological, pathological or external conditions, the number of chromosomes will change. Some congenital diseases are caused by the variation of chromosome number, such as congenital idiot, which is caused by an extra chromosome on chromosome 2 1. Therefore, it is of great significance to carry out chromosome research for early diagnosis of diseases, prenatal genetic counseling and improvement of national quality.

The human body * * * has 23 pairs of chromosomes, of which 22 pairs are autosomes, the remaining pair (2) are sex chromosomes, and women have 2 X chromosomes, namely XX karyotype; Men have 1 x chromosome and 1 y chromosome, that is, XY karyotype. X chromosome contains 1 100 genes, accounting for about 5% of the human genome, and information that may help to improve the diagnostic accuracy of hemophilia, blindness, autism, obesity and leukemia. The study, discovered by the International Association of Scientists, shows that women are more "fickle" than previously thought, and their genes are more complicated than those of men. Dr. Mark Ross of the Sanger Institute of Wellcome Trust, which leads the International Association of Scientists, said: "In terms of genetic model, unique biology and connection with human diseases, X chromosome is undoubtedly the most unusual in the human genome."

We can find chromosomes in every nucleus. Chromosomes contain genes that determine a person's personality. Women have two X chromosomes, while men have one X and one Y chromosome respectively. These two different chromosomes determine their male characteristics. The results of scientists' research show that the Y chromosome is an eroded X chromosome with few genes. The results of this study will be published in the latest issue of Nature. The X chromosome is larger than the Y chromosome, because women have two X chromosomes, and the activity of one X chromosome is largely cut off or inactive.

Professor Laura Karel of Pennsylvania State University School of Medicine pointed out that not all genes on the X chromosome are inactivated, which may explain some differences between men and women. Professor Karel also published her findings in the journal Nature. The degree of inactivation of X chromosome also varies greatly among women. Professor Karel said in a statement: "These effects of inactivating X chromosome genes may explain some differences between men and women. Some differences between men and women have nothing to do with sex chromosomes. "

Genetic mutations and diseases such as color blindness, autism and hemophilia often affect men because men do not have another X chromosome to "compensate" for these diseases. Color blindness, autism, hemophilia and other diseases are all related to X chromosome. There are many genes related to mental retardation on the X chromosome, and the largest gene in the human genome is called DMD. The mutation of DMD gene can cause muscular dystrophy in Du Xing, which can make men lose their ability to work and even die.

Dr David Michael Bentley of the Sanger Institute of Wellcome Trust said: "There are other diseases related to the X chromosome. By studying where there is a problem, we can better understand the biological process of the normal body. " (