Each DNA molecule is made of four types of chemical building blocks called nucleotides . The linear sequence of these four nucleotides encode the precise information in a gene , the unit of inheritance from parent to offspring. An organism's complex structural organization is specified by an enormous amount of coded information. Passing the information encoded in DNA from parent to offspring.
All forms of life use essentially the same genetic code.
A particular nucleotide sequence provides the same information to one organism as it does to another. Differences among organisms reflect differences in nucleotide sequence. A feeling for organisms enriches the study of life We may study life at structural levels below or above the organism, but it is organisms that first attract us. A feeling for the organisms we seek to understand enriches our study of life at all levels. Barbara McClintock is a good example of a biologist whose feeling for the organism contributed to an important scientific discovery.