Genetics is a discipline of biology.It is the science of heredity and variation of traits (characteristics) in living organisms, and the study of genes.In the laboratory, genetics proceeds by mating carefully selected organisms, and analysing their offspring. More informally, genetics is the study of how parents pass some of their characteristics to their children. It is an important part of biology, and gives the basic rules on which evolution acts.The fact that living things inherit traits from their parents has been known since prehistoric times, and used to improve crop plants and animals through selective breeding. However, the modern science of genetics, which seeks to understand the process of inheritance, only began with the work of Gregor Mendel in the mid-nineteenth century. Although he did not know the physical basis for heredity, Mendel observed that organisms inherit traits via discrete units of inheritance, which are now called genes.