Copyright © 2007 Dorling Kindersley
Genetic engineering is the manipulation of genes of living things. Scientists can now insert genes from one organism into another. They do this to grow GM FOOD. They can also CLONE embryos that provide STEM CELLS to repair damaged body tissue.
The differences between species and between individuals are explained by the differences in their genes. Sexual reproduction, which randomly mixes genes from parents in their children, produces variation from generation to generation.
When dog breeders select puppies with short tails to breed from, they are manipulating the gene for tail length. The gene for short tails is passed on, and the gene for long tails dies out. Now, scientists can select and move genes between organisms in the laboratory. A gene for disease resistance can be “snipped out” from the DNA of one plant and inserted into another.
The first genetically modified (GM) food went on sale in 1994. It was a variety of tomato called Flavr Savr. The gene that makes the tomato soften had been changed to make it ripen more slowly, so that it would develop more flavor.
Some farmers are not eager to grow GM crops. One worry is that genes introduced into the crop will transfer to other species. Another concern is that herbicide- and pesticide-resistant crops encourage farmers to use too many of these chemicals, which might damage wildlife.
In the 1960s, scientists tried to breed crops to match conditions in developing countries. The aim was to reduce food shortages by introducing productive crops that were disease resistant. In India, crop production increased, but in other places, the new crop varieties needed fertilizers that farmers could not afford.
Clones are different individuals with the same genes. Clones are common in nature—a bacterium clones itself by splitting in two, producing two identical bacteria. Now scientists have developed artificial cloning techniques that work with mammals.
The first clone made with DNA from an adult animal was Dolly the sheep in 1997. DNA was taken from an adult sheep (Dolly’s biological mother) and inserted into an egg cell (with its own DNA removed) from another sheep. The cell started to divide, and the embryo was taken and put into the womb of a third sheep—Dolly’s surrogate (birth) mother. Animal clones could be used for medical research.
Many plants propagate (reproduce) vegetatively (without sex). Each new plant has the same DNA as the parent and is therefore a clone. On a plantation, all the banana plants are clones of their parents.
The starter cells in an embryo are called stem cells. As the embryo grows, stem cells change to become the different cells needed in the body, such as nerve cells and blood cells.
Stem cell research is investigating the use of stem cells to repair damaged or diseased tissue. For example, the body cannot repair or replace nerve cells damaged by disease or injury. Transplanted stem cells could be grown to develop into new nerve cells to treat Parkinson’s and Alzheimer’s diseases.
Stem cell research is controversial because the cells are taken from human embryos that have been fertilized in the laboratory. To avoid rejection of the cells, the embryo should ideally have been cloned using the patient’s DNA. Many people have concerns about using human embryos in this way.