Chapter 19: Genetic Technology

Recombinant DNA

Recombinant DNA (rDNA) is a technology that uses enzymes to cut and paste together DNA sequences of interest. The recombined DNA sequences can be placed into vehicles called vectors that ferry the DNA into a suitable host cell where it can be copied or expressed.

Recombinant DNA is the method of joining two or more DNA molecules to create a hybrid. The technology is made possible by two types of enzymes, restriction endonucleases and ligase. A restriction endonuclease recognizes a specific sequence of DNA and cuts within, or close to, that sequence. By chance, a restriction enzyme’s recognition sequence will occur every (¼)n bases along a random DNA chain.

Genetic Engineering

Recombinant DNA is the method of joining two or more DNA molecules to create a hybrid. The technology is made possible by two types of enzymes, restriction endonucleases and ligase. A restriction endonuclease recognizes a specific sequence of DNA and cuts within, or close to, that sequence. By chance, a restriction enzyme’s recognition sequence will occur every (¼) n bases along a random DNA chain.

Step 1: DNA Extraction
The process of genetic engineering requires the successful completion of a series of five steps.

DNA extraction is the first step in the genetic engineering process. In order to work with DNA, scientists must extract it from the desired organism. A sample of an organism containing the gene of interest is taken through a series of steps to remove the DNA.

Step 2: Gene Cloning
The second step of the genetic engineering process is gene cloning. During DNA extraction, the entire DNA from the organism is extracted at once. Scientists use gene cloning to separate the single gene of interest from the rest of the genes extracted and make thousands of copies of it.

Step 3: Gene Design
Once a gene has been cloned, genetic engineers begin the third step, designing the gene to work once inside a different organism. This is done in a test tube by cutting the gene apart with enzymes and replacing gene regions that have been separated.

Step 4: Transformation
The modified gene is now ready for the fourth step in the process, transformation or gene insertion.

Since plants have millions of cells, it would be impossible to insert a copy of the transgene into every cell. Therefore, tissue culture is used to propagate masses of undifferentiated plant cells called callus. These are the cells to which the new transgene will be added.

The new gene is inserted into some of the cells using various techniques. Some of the more common methods include the gene gun, agrobacterium, microfibers, and electroporation. The main goal of each of these methods is to transport the new gene(s) and deliver them into the nucleus of a cell without killing it. Transformed plant cells are then regenerated into transgenic plants. The transgenic plants are grown to maturity in greenhouses and the seed they produce, which has inherited the transgene, is collected. The genetic engineer’s job is now complete. He/she will hand the transgenic seeds over to a plant breeder who is responsible for the final step.

Step 5: Backcross Breeding
The fifth and final part of producing a genetically engineered crop is backcross breeding. Transgenic plants are crossed with elite breeding lines using traditional plant breeding methods to combine the desired traits of elite parents and the transgene into a single line. The offspring are repeatedly crossed back to the elite line to obtain a high yielding transgenic line. The result will be a plant with a yield potential close to current hybrids that expresses the trait encoded by the new transgene.

  • Genetic engineers need the following to modify an organism:
    • Enzymes (restriction endonucleases, ligase and reverse transcriptase)
    • Vectors – used to deliver genes into a cell (eg. plasmids, viruses and liposomes)
    • Markers – genes that code for identifiable substances that can be tracked (eg. GFP – green fluorescent protein which fluoresces under UV light or GUS – β-glucuronidase enzyme which transforms colorless or non-fluorescent substrates into products that are coloured or fluorescent)

Genetic Screening

Genetic screening is the process of testing a population for a genetic disease in order to identify a subgroup of people that either have the disease or the potential to pass it on to their offspring. Genetic testing involves examining your DNA, the chemical database that carries instructions for your body’s functions. Genetic testing can reveal changes (mutations) in your genes that may cause illness or disease.

Genetic screening is the testing of an embryo, fetus or adult to analyze the DNA. BRCA1 and BRCA2 are genes that produce tumor suppressor proteins and thus they play an important role in regulating cell growth. Genetic screening helps to find if the person has these mutations.

Cystic Fibrosis

Cystic fibrosis (CF) is an inherited disorder that causes severe damage to the lungs, digestive system and other organs in the body. Cystic fibrosis affects the cells that produce mucus, sweat and digestive juices. These secreted fluids are normally thin and slippery. Cystic fibrosis is an inherited disease caused by Mutation in a gene called the cystic fibrosis trans membrane conductance regulator (CFTR) gene. The CFTR gene provides instructions for the CFTR protein.

Gene Therapy

Gene therapy is an experimental technique that uses genes to treat or prevent disease. In the future, this technique may allow doctors to treat a disorder by inserting a gene into a patient’s cells instead of using drugs or surgery. Gene therapy involves altering the genes inside your body’s cells in an effort to treat or stop disease. Genes contain your DNA — the code that controls much of your body’s form and function, from making you grow taller to regulating your body systems. Genes that don’t work properly can cause disease. The process of gene therapy involves;

  • Creating a working gene.
  • Building a therapeutic vector.
  • Determining eligibility.
  • Delivering the working gene.
  • Monitoring safety and efficacy.

There are two types of gene therapy and they are:

  1. Somatic gene therapy: Somatic gene therapy can be defined as the ability to introduce genetic material (RNA) into an appropriate cell type or tissue in vivo in such a way that it alters the cell’s pattern of gene expression to produce a therapeutic effect.
  2. Germ line gene therapy: Germline gene therapy is when DNA is transferred into the cells that produce reproductive cells, eggs or sperm, in the body. This type of therapy allows for the correction of disease-causing gene variants that are certain to be passed down from generation to generation.

Genetically modified Organisms in Agriculture

A genetically modified organism (GMO) is an animal, plant, or microbe whose DNA has been altered using genetic engineering techniques. For thousands of years, humans have used breeding methods to modify organisms. Corn, cattle, and even dogs have been selectively bred over generations to have certain desired traits.

GMO crops that are tolerant to herbicides help farmers control weeds without damaging the crops. When farmers use these herbicide-tolerant crops they do not need to till the soil, which they normally do to get rid of weeds. This no-till planting helps to maintain soil health and lower fuel and labor use. Crop plants have been genetically modified to be:

  • Resistant to herbicides – increases productivity / yield
  • Resistant to pests – increases productivity / yield
  • Enriched in vitamins – increases the nutritional value

Scientists have genetically modified many organisms including bacteria (eg. to produce insulin), sheep (eg. to produce a human blood protein known as AAT), and maize (eg. to be resistant to insect attacks), rice (eg. to produce β-carotene to provide vitamin A).

Use of GMO’s in Agriculture

  • increased crop yields
  • reduced costs for food or drug production
  • reduced need for pesticides
  • enhanced nutrient composition and food quality
  • resistance to pests and disease
  • Greater food security and medical benefits to the world’s growing population.
  • GMOs have reduced pesticide applications by 8.2%and helped increase crop yields by 22%. … Avoiding plastic straws may be one way that people are trying to help, but allowing farmers to plant GMO crops to help preserve soil, conserve water, and reduce carbon emissions is another way.