Rhode Island Department of Health Genetics Website

About Genetics

Genetics is the study of genes, how they function and the environmental factors that determine whether, and to what extent, genes are expressed. Genes carry the messages of our inheritance from generations of our ancestors; they carry the key to our similarities and our uniqueness. When genes are working correctly, our bodies develop and function smoothly. But if there is a defect in one gene – or even a small part of a single gene - the effect can be dramatic: deformities and disease, even death.

DNA is the molecular code that carries the genetic "map" from generation to generation. DNA, which carries the instructions that allow cells to make proteins, is made up of four chemical bases: adenine, cytosine, guanine and thymine (A,C,G,T). These bases make up the rungs of the DNA ladder: adenine always pairs with thymine and cytosine always pairs with guanine. Instructions are written in sequences of these four letters, and they tell a cell how to make a particular protein.

A gene is a segment of DNA that carries the instruction for a single protein. Genes are strung together on chromosomes, which are very long strands of DNA tightly coiled inside the cell. Humans have about 30,000 to 40,000 genes. Each human cell has about 3 billion base pairs of nuclear DNA. These 3 billion base pairs make up the human genome. The study of all of the genes that make up an organism is called genomics. The Human Genome Project (HGP) began in the 1980’s to characterize the human genome.

 Amazing new techniques have been developed that allow scientists to learn a great deal about how genes work and how genes are linked to disease. Increasingly, researchers are able to identify mutations, changes within genes that can lead to specific disorders. Tests for gene mutations make it possible not only to detect diseases already in progress but also, in certain situations, to foresee diseases yet to come. This new ability raises both high hopes and grave concerns. On the one hand, predictive gene testing holds out the possibility of saving thousands of lives through prevention or early detection. On the other, the implications of test results are enormous, not only for the individual but also for relatives who share this genetic legacy, and for society as a whole.