In legal terms, inheritance describes the wealth that parents leave, or pass on, to their children. In biology, the word refers to the genetic processes by which parents endow their children with specific traits, like height, hair color, eye color, and other characteristics.
In order to understand why the laws of inheritance work as they do, scientists had to look into the interior of cells. Cells are the building blocks of life, and all living things—from bacteria to human beings—are composed of them.
Genes contain coded information that leads to the production of proteins. Proteins, in turn, are responsible for creating the traits that characterize individual organisms.
The discoveries of twentieth-century genetics in general, and the Human Genome Project in particular, have launched medicine on a whole new course. Rather than waiting for diseases to develop and then treating them with drugs or surgery, doctors are now embarked on finding the genetic causes of disease in the hope of fixing the malfunctioning gene before the illness even begins to show its early symptoms.
Besides blazing new paths in health science, genetics is transforming the way in which criminal investigations and trials are conducted. The importance of DNA evidence rests on a single but crucial fact: Every individual's DNA is unique (except in the case of identical twins, who have identical genomes).
The genetic revolution holds out great promise in medicine and many other fields. At the beginning of the twenty-first century, rapid advances in this relatively new science have put within humanity's grasp the ability to cure or prevent previously incurable diseases.