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Basic Genetics - FAQs

What are genetics and molecular medicine?

While its practical implications are broad, genetics essentially is the study of how specific biological traits and characteristics are transmitted to us by our parents. Molecular medicine examines how illness and disease occurs or can be prevented at the cellular or molecular level.

What are the “building blocks” of genetics and molecular medicine?

  • A cell is the individual unit from which tissues of the body are formed
  • DNA is the double-stranded molecule that encodes genetic information in the nucleus of cells. A DNA strand is composed of four different nucleotides or base pairs (adenine, guanine, cytosine, and thymidine). It determines the structure, function and behavior of the cell. In animals and plants, long strands of DNA are arranged into structures called chromosomes
  • Genes are sometimes known as the physical unit of heredity. Genes are formed from DNA, carried on the chromosomes and are responsible for the inherited characteristics that distinguish one individual from another. Each human individual has an estimated 30,000 separate genes.
  • Chromosomes are the self-replicating genetic structures of cells. They contain the cellular DNA that bears in its nucleotide sequence the linear array of genes.
  • RNA is the single-stranded molecule that is transcribed from DNA and ultimately translated into a chain of amino acids that form a protein.
  • Proteins are the principal constituents of the protoplasm of all cells. Each protein has a unique, genetically defined amino acid sequence that determines its specific shape and function.
  • A genome is the total set of genes carried by an individual or cell. The human genome consists of approximately 3 billion base pairs. By contrast, the genome of mouse contains approximately 2.5 billion base pairs while that of a fruit fly is approximately 0.2 billion base pairs.

How do genes work?

While each cell contains a full complement of DNA, a normal cell activates just the genes it needs at the moment and actively suppresses the rest. Some genes enable cells to make proteins needed for basic functions, some play a role in early development of the embryo and are then shut down forever, and many encode proteins that are unique to a particular kind of cell and that give the cell its character - making a brain cell, say, different from a bone cell.

How are genes linked to disease?

Many, if not most, diseases have their roots in our genes. Genes determine everything from how efficiently we process foods to how vigorously we respond to infections. More than 4,000 diseases are thought to stem from mutated genes inherited from at least one parent. Common disorders such as heart disease and most cancers arise from a complex interplay between multiple interacting genes (genetic susceptibility) and environmental factors. Individual susceptibility to these common disorders is often associated with prevalent DNA variations in the human genome (polymorphisms).

What is gene therapy?

Gene testing involves examining a person's DNA for some anomaly that could cause or increase the risk for a disease or disorder. The DNA usually is taken from cells in a sample of blood or occasionally from other body fluids or tissues. In addition to studying chromosomes or genes, genetic testing in a broader sense can also include biochemical tests for the presence or absence of key proteins that signal aberrant genes.

What is cloning?

Cloning simply means making copies of a single molecule, cell, virus or bacterium. There are many different kinds of cloning, most of which are commonly used medical tools. Over the last decade, various types of cloning have allowed scientists and researchers to:

  • Develop powerful new drugs
  • Produce insulin and useful bacteria in the lab
  • Track the origins of biological weapons
  • Catch criminals and free innocent people

Human reproductive cloning aims to create human beings by cloning human embryos. Almost all patient advocacy groups and leading science organizations, including the National Academy of Sciences, agree that human reproductive cloning should not be pursued.

Human therapeutic cloning involves the cloning of human embryos for the purpose of extracting stem cells that can be used to repair tissues and organs. Unlike reproductive cloning, embryos for therapeutic cloning are grown in laboratory cultures and are not implanted in the female reproductive tract.

What is a stem cell?

A stem cell is an immature cell that has the potential to become specialized into different types of cells throughout the body. There are two basic types of stem cells: adult stems cells and embryonic stem cells. Embryonic stem cells are produced when a newly fertilized egg begins to divide. These stem cells can become any type of cell in the body.

Adult stem cells – somewhat of a misnomer because they can also be found in infants and children – are stem cells that reside in already developed tissue. These stem cells act like a repair system, dividing regularly to provide the new body with specialized cells to take the place of those that die or are lost. Common adult stem cells are nerve, blood, muscle, skin and bone.

What is the Human Genome Project?

Every cell of every living organism contains the master blueprint for all cellular structures and activities for the lifetime of the organism. The complete set of instructions for making a person is known as the human genome. The U.S. Human Genome Project is an effort coordinated by the Department of Energy and the National Institutes of Health that aims to:

  • identify all the approximately 30,000 genes in human DNA,
  • determine the sequences of the 3 billion chemical base pairs that make up human DNA,
  • store this information in databases,
  • improve tools for data analysis,
  • transfer related technologies to the private sector, and
  • address the ethical, legal, and social issues (ELSI) that may arise from the project.

Other genetics resources on the web

Genetics Home Reference - the National Library of Medicine's Web site for consumer information about genetic conditions and the genes or chromosomes responsible for those conditions.

Human Genome Project Information - suite of Web sites sponsored by US Dept of Energy containing information on the Human Genome Project and related subjects in genetics.

Learn more about applied genetics and genetics policy issues

Sources:
AMA Science
DNA Sciences, Inc.
Oak Ridge National Laboratory, a laboratory managed for the U.S. Department of Energy
Genetic Science Learning Center, University of Utah
College of Biotechnology, University of Saskatchewan
BBC News, July 31, 2000. “Q&A: Therapeutic human cloning”