Genetics is the study of genes, genetic variation, and heredity in living organisms. A gene is the basic physical and functional unit of heredity. Genes, which are made up of DNA, act as instructions to make molecules called proteins.
The Human Genome Project has estimated that humans have 20,000 - 25,000 genes. Every person has two copies of each gene, one inherited from each parent. Most genes are the same in all people, but less than 1% of genes are slightly different between people. Poplar tree genome suggests more than 45,000 genes.
A genetically modified organism (GMO) is any organism whose genetic material has been altered using genetic engineering techniques (i.e., a genetically engineered organism). GMOs are used to produce medications and genetically modified foods, and are widely used in scientific research and the production of other goods.
A more specifically defined type of GMO is a "transgenic organism." This is an organism whose genetic makeup has been altered by the addition of genetic material from an unrelated organism. Typically GMOs are organisms whose genetic makeup has been altered without the addition of genetic material from an unrelated organism.