The Human Genome
Scientists completed an incredible project during the summer of 2000. They finished mapping the human genome, which is like saying they mapped the complete set of instructions for making a human being. Although the human genome is very tiny in size (it fits into the nucleus of every cell in your body), it is very large in information. (Just reading a list of the 3 billion base pairs of DNA that comprise the human genome would take about 9.5 years, if you read about 10 pairs per second and didn't stop.) The particular order of the base pairs is called the DNA sequence. It is this sequence that specifies the exact genetic instructions required to create a particular organism with its own unique traits.
Each time a cell divides, its full genome is duplicated. During cell division the DNA molecule unwinds and the weak bonds between the base pairs break, allowing the strands to separate. Each strand directs the synthesis of a complementary new strand. Strict adherence to base-pairing rules ensures that the new strand is an exact copy of the old one. This minimizes the incidence of subtle DNA abnormalities (mutations) that are responsible for many inherited diseases such as cystic fibrosis. The strands of DNA comprise four chemical units or letters used over and over again in varying chemical sequences. These letters form the genes.
A gene is the basic physical and functional unit of heredity. It is capable of reproducing itself exactly at each cell division. Each DNA molecule contains many genes; the human genome is estimated to contain approximately 80,000-100,000 genes.
The 3 billion base pairs of DNA in the human genome are organized into 23 distinct, physically separate microscopic units called chromosomes. All genes are arranged linearly along the chromosomes. The nucleus of most human cells contains two sets of chromosomes, one set given by each parent. The Human Genome Project has now successfully mapped this incredible amount of information. It was an achievement of historic proportion. This new knowledge is expected to speed the identification of the tens of thousands of human genes, an important step that will hopefully answer many questions such as ways to prevent illness, or earlier diagnosis of life-threatening diseases,or lead to the discovery of new drugs and treatments for diseases. Indeed, some have predicted that the 21th century will be called "The Biology Century".