Selective Breeding Selective Breeding is when someone (humans) breed organisms with specific traits in order to produce offspring having those same traits. This is also called artificial selection, the process of selecting a few organisms with desired traits to serve as parents of the next generation. Through selective breeding, different species of dogs have been created, all descendents of the gray wolf. However, this takes TIME (as in decades or centuries)! What is Genetic Engineering? What is genetic engineering? Genetic engineering is the process of manually adding new DNA to an organism. The goal is to add one or more new traits that are not already found in that organism. This happens much faster than with traditional selective breeding. Examples of genetically engineered (transgenic) organisms currently on the market include plants with resistance to some insects, plants that can tolerate herbicides, and crops with modified oil content. 1
genetic engineering.notebook What is Genetic Engineering? Small segments of DNA are called genes. Each gene holds the instructions for how to produce a single protein. Proteins do the work in cells. Everything you see in an organism is either made of proteins or the result of a protein action. DNA is a universal language, meaning the genetic code means the same thing in all organisms. It would be like if all cookbooks around the world were written in a single language that everyone knew. This characteristic is critical to the success of genetic engineering. When a gene for a desirable trait is taken from one organism and inserted into another, it gives the recipient organism the ability to express that same trait. How is Genetic Engineering done? Genetic engineering works by physically removing a gene from one organism and inserting it into another, giving the second organism the ability to express the trait encoded by that gene. 1) First, find an organism that naturally contains the desired trait. 2) The DNA is extracted from that organism. 3) The one desired gene is located and copied from thousands of genes that were extracted. This is called gene cloning. 1) 3) 2) 2
How is Genetic Engineering done? 4) The gene may be modified slightly to work in a more desirable way once inside the recipient organism. 5) The new gene(s), called a transgene, is delivered into cells of the recipient organism. This is called transformation. However, genetic engineers have no control over where or if the transgene inserts into the new genome. As a result, it takes hundreds of attempts to achieve just a few transgenic organisms. 6) Once a transgenic organism has been created, traditional breeding is used to improve the characteristics of the final product. So genetic engineering does not eliminate the need for traditional breeding. It is simply a way to add new traits to the pool. Genetically Modified Organisms Genetically Modified Organisms, or GMOs are when a gene from one organism is purposely moved to improve or change another organism in a laboratory. These are also called transgenic organisms (for transfer of genes). Transgenic crops are created to breed plants with a certain desirable trait. We used to do this through selective breeding, but selective breeding transferred not only the traits we wanted, but also other unwanted traits. Genetic modification lets us introduce new traits one at a time without complications from extra genes. 3
Genetic Engineering and Controversy Since about 2/3 of food in supermarkets has been genetically modified, some people are concerned about potential problems. Genetically modified foods are intended to have better nutrition, have higher crop yields, and be better for the environment because they need less pesticides. Other groups worry about scientists working "outside natural boundaries" and creating things that wouldn't typically be made on their own in nature. They worry about unforeseen consequences that occur when an organism's genes are changed. Scientists claim that using genetic engineering is safer than "traditional" selective breeding techniques, because only the wanted gene is transferred, not other genes as well. Gene Therapy The most common type of Gene Therapy being done is Somatic Gene Therapy. This introduces a "good" gene into targeted cells to treat the patient but not the patient's future children because these genes do not get passed along to offspring. In other words, even though some of the patient's genes may be altered to treat a disease, it won't change the chance that the disease will be passed on to the patient's children. 4
Gene Therapy To cure genetic diseases, scientists must first figure out which gene or set of genes causes each disease. The Human Genome Project and other international efforts have completed the initial work of sequencing and mapping virtually all of the 25,000 genes in the human cell. This research will provide new strategies to diagnose, treat, cure, and possibly prevent human diseases. Although this information will help scientists determine the genetic basis of many diseases, it will be a long time before diseases actually can be treated through gene therapy. One day it may be possible to treat an unborn child for a genetic disease even before symptoms appear. 5