人体的构造和功能是很微妙的,各器官、各系统之间复杂而又协调地工作,维持着个体的生存。每个人的一切性状又都是由一定的遗传物质通过环境的作用而形成的。所谓遗传物质就是脱氧核糖核酸(DNA)。在细胞分裂中期,DNA形成一些可以在显微镜下直接能观察到的短粗杆状物即染色体。人类染色体的数目和结构是相当稳定的,不因种族、肤色和地区而有所不同,也就是说每个人身体里的每个细胞都同 The structure and function of the human body are subtle, and the organs and systems work in a complex and coordinated way to maintain the individual’s existence. All of the traits of each person are formed by the role of certain genetic material through the environment. The so-called genetic material is deoxyribonucleic acid (DNA). In the middle of cell division, DNA forms stubby rods or chromosomes that can be directly visualized under a microscope. The number and structure of human chromosomes is fairly stable and does not vary by race, color and region, meaning that every cell in everybody’s body shares the same