Pestacides

. Genetic engineering involves the alteration of an organisms hereditary material in order to eliminate undesirable characteristics or to produce plants with more desirable characteristics. The splicing of genes takes place in order to combine traits that would be unlikely to occur together under ordinary circumstances. Practices that go back centuries, such as the use of microbes to make wine and cheese and the selective breeding of livestock and crops, are example of biotechnology. (Campbell, 1999) These, and other, procedures have relied on mutation and genetic recombination. Biotechnology that is based on manipulation of DNA is different from earlier practices because it enables scientists to modify specific genes and move them from organisms as distinct as bacteria, plants, and animals. The actual splicing of genes into foreign genomes is very complex. Many varieties of full-grown adult plants can regenerate from single, modified plant cells called protoplasts  plant cells whose cell walls have been removed by enzymatic digestion. (Peters) Plats that can be cloned easily include carrots, tomatoes, potatoes, petunias, and cabbage. Being able to grow a whole new plant from one cell means that researchers can engage in the genetic manipulation of the cell, let the cell develop into a complete plant and examine the physical and growth effects of the genetic manipulation within a short period of time. The results of genetic engineering in plants are easier to examine than the same process in animal cells. A new technique known as recombinant DNA, or gene splicing, will allow scientists to alter an organisms genes directly by joining its DNA to the DNA of a second organism. The result is recombinant DNA that permanently changes the genetic makeup of the organism and alters the proteins that its cells produce. This change will then be passed on to descendants of the genetically altered organism. In most cases the splicing involves recombining the donors desirable genes with the DNA from a vector, which will carry the donor DNA into the host. Many times the host will be a bacterium, which will reproduce and multiply the recombinant DNA producing large quantities of the desired protein. In some cases, DNA can be introduced directly into an organism by injection into reproductive cells. (Encarta, 1999) The most commonly used plant-cloning vector is the Ti plasmid; otherwise know as the tumor-inducing plasmid. This plasmid may be found in cells of the bacterium known as Agro bacterium tumefaciens lives in soil. This bacterium has the ability to infect plants causing a tumorous lump called a crown gall, which forms at the site of infection. The studied plasmid is a large, circular, double-stranded DNA molecule that can replicate independently of the genome. When the bacteria infect a plant cell a 30,000 base pair segment of the Ti plasmid separates from the plasmid and incorporates into the host cell genome. This aspect of Ti plasmid function has made it useful as a plant cloning vector. (Peters) One of the earliest experiments that involved the transport of a foreign gene by the Ti plasmid involved the insertion of a gene isolated from a bean plant into a host tobacco plant. This experiment may have served no commercially useful purpose but it successfully established the ability of the Ti plasmid to carry genes into plant host cells, where they could be incorporated and expressed. Unfortunately many important crop plants, such as corn, rice and wheat, are monocotyledons, plants with one embryonic leaf, which