Genetics
Genetics is a science that studies the inheritance and variation of organisms, and is an important branch of biology. In prehistoric times, people have used the genetic characteristics of organisms to improve the yield of grain and livestock by selecting breeding. The modern genetics, whose purpose is to seek the mechanism of understanding the whole process of inheritance, begins with the study of Mendel in the mid-19th century. Although Mendel did not know the genetic basis of the genetic, but he observed the genetic characteristics of the organism, some genetic units to comply with simple statistical laws, these genetic units are now known as genes. Genes are located on DNA, whereas DNA is a chain molecule consisting of four different classes of nucleotides. The nucleotide sequence on DNA is the genetic information of the organism. Natural DNA exists in double-stranded form, and the nucleotides are complementary to each other, and each strand can be used as a template to synthesize new complementary strands. This is the way in which genes can be genetically replicated. ...