Chapter 2 What is genetic engineering Every living thing is made up of tiny units called cells Each cell contains a set of instructions known as its genetic code or genome which controls everything that happens in the organism Genetic engineering is a technique that can be used to change the genetic code of a living organism Chromosomes and DNA The genetic information is contained in tiny double-stranded threadlike structures inside the nucleus These threads are called chromosomes and each piece of information that they carry is called a gene Geneticists often visualize the genes lined up along the Inside a cell DNA double helix Cell Chromosomes Nucleus Genes 10 chromosomes like beads on a necklace Chromosomes contain a chemical called deoxyribonucleic acid DNA which has a complicated double helix structure made up from pairs of molecules called bases There are four bases adenine A cytosine C guanine G and thymine T Each gene is made up of a specific sequence of bases This diagram shows the set of 23 chromosomes that make up the human genome Each chromosome contains many genes and each gene is made from linked base pairs of DNA 1 7 2 8 3 9 4 5 6 10 11 12 13 14 15 16 17 18 19 20 22 21 Genome X Y
Geneticists have worked out the sequence of genes and the sequence of bases that make up the genes for many organisms This means that they know which part of a chromosome carries the gene for a particular characteristic and exactly what the code is for each gene What is genetic engineering Expert View We’ll have plants that survive drought We’ll have plants that have more nutrition And we’ll have plants that have new uses and be able to benefit the farming community the economics of farming as well as the environment Roger Beachy plant pathologist talking about the benefits of genetic engineering 2007 Changing chromosomes By using enzymes to split a DNA molecule at two precise points it is possible to remove a gene from a chromosome Scientists can take a gene from the chromosome of one organism and insert it into the chromosome of another organism This means that they can transfer a characteristic of one organism into another This is the basis of genetic engineering An organism whose genetic code has been changed by genetic engineering is said to have been genetically modified often shortened to GM Swapping genes Genes can be swapped within a species to create new combinations For example a gene from a plant variety that produces a few large fruits might be transferred to the genome of a plant from the same variety that produces many small fruits giving a new variety that produces many large fruits These fruits are the result of genetic engineering between plums and apricots The fruits on the left are apriums and those on the right are pluots 11
Is Our Food Safe Genes can be swapped from the genome of one organism into the genome of a very different organism For example ordinary tomato plants cannot survive cold weather To create a tomato that can scientists looked for an organism that could survive cold conditions They chose a dogfish a small shark removed the frost resistant gene from its chromosomes and inserted this gene into tomato plant chromosomes The resulting organism has all the usual tomato plant characteristics plus the frost-resistant characteristic of the dogfish How are GM foods created Creating a genetically modified organism is a slow and expensive process On average it can take between five and 10 years and cost as much as 50 million to 100 million First scientists have to decide which organism they want to modify This is called the host organism since it is the one that will receive the new genetic material Then scientists must identify which characteristic of the host organism they want to modify The next step is to identify an organism that has the characteristic the scientists want to transfer to the host This is called the donor organism since genetic material will be taken from it Having found a suitable donor organism the scientists need to analyze its genome to find the gene or genes that carry the code for the specified characteristic FOCUS GM success Stuart Armitage and his family began to grow cotton in Australia in 1993 From the beginning the Armitages had trouble with a pest called the corn earworm They found it difficult and expensive to control the earworm with chemical sprays In 1999 they switched to a GM variety of cotton called Bollgard II which seems to have solved their problems Stuart says Thanks to Bollgard II cotton we now have a more relaxed family life no spraying every other night of the week and I feel good about our pest management practices The third step is to extract the gene or genes that carry the code for the required characteristic from the rest of the donor organism’s DNA Enzymes are used to do this splitting the DNA at very precise points to extract only the section that is needed The fourth step is to insert this piece of donor DNA into the host organism This procedure can be carried out in several different ways but the oldest and most common 12
What is genetic engineering method is creating recombinant DNA In this technique the gene is inserted into a ring of DNA called a plasmid from a bacterium or virus The bacterium or virus is then injected into the host cells and the new gene finds its way into the host’s DNA The bacterium or virus thus acts as a carrier or vector for the gene that is being transferred into the host Creating recombinant DNA Host plant red tom ato Bacterium w ith plasm id Bacterium put into host plant cell Gene for yellow ness inserted into plasm id Gene for yellow ness extracted Donor plant yellow pepper New plant yellow tom ato In this example of genetic engineering a gene for yellowness is transferred from a yellow pepper plant via a bacterium to a red tomato plant The process creates a new plant that will produce yellow tomatoes Once the new gene has been inserted the host organism can be grown and tested Scientists check that the new gene has been incorporated into the organism’s genome and that the new characteristic is present Further tests must prove that the organism has not been changed in some other unexpected way that makes it harmful dangerous or less viable than the original Initial tests are on a small number of organisms in a closely controlled environment When scientists are sure the organism is safe larger-scale tests on more organisms can be done Finally full commercial-scale trials can take place Once all the testing stages are complete the organism may be licensed and released for commercial use 13
