Unit 06: Genetically Modified Organisms (GMOs)

Defining Genetically Modified Organisms (GMOs)

• General Genetic Variation: All living organisms undergo genetic modification naturally. Sexually reproducing organisms intentionally modify genetic material during reproduction to create variation in offspring. Asexual organisms, such as bacteria, experience variation through random genetic mutations.

• Societal Definition: In a societal context, terms like genetic engineering, genetic modification, and GMOs refer specifically to human-introduced changes to plants and animals.

• World Health Organization (WHO) Definition: A GMO is an "organism(s) in which the genetic material (DNA) has been altered in a way that does not occur naturally by mating and/or natural recombination."

• The Laboratory Factor: True GMO variation results from human manipulation in a laboratory environment rather than through natural reproductive processes.

Specific Categories of Genetic Modification

• Transgenic:

  • Prefix "trans-" means "across."

  • DNA from a target species is modified by inserting a gene or gene portion from a completely different species (e.g., a human gene in a pig or a bacterial gene in a plant).

• Cisgenic:

  • Prefix "cis-" means "the same."

  • The DNA of the target organism is modified using genes from the same species to alter physical characteristics.

• Intragenic:

  • Prefix "intra-" means "within."

  • Pieces of the organism's own genetic information are rearranged or modified to improve a specific characteristic.

The History and Prevalence of GMOs

• Long-term Human Interference: Humans have altered genetics for millennia through interfering with natural reproduction. Examples include dogs, wheat, and strawberries.

• Selective Breeding:

  • Humans identify natural variation in traits (e.g., fruit size, dog size) and breed individuals with those traits to produce specific offspring.

  • Gregor Mendel used a form of selective breeding with pea plants to create "true-breeding" versions.

• The First Laboratory GMO: The bacterium $Escherichia\,coli$ ($E.\,coli$) was the first organism to have its DNA directly manipulated in a lab.

• The First Food GMO: The Flavr-savr tomato (approved in 1994 by Calgene) was the first GMO for human consumption. It inhibited the gene that produces an enzyme responsible for dissolving pectin in the skin, which normally causes over-ripening and softening.

• Modern Prevalence (Planted Acreage in the U.S. as of 2023):

  • Herbicide-tolerant Soybeans: Approximately $95\%$ of planted acres.

  • Herbicide-tolerant Cotton: Approximately $92\%$ of planted acres.

  • Herbicide-tolerant Corn: Approximately $90\%$ of planted acres.

  • Insect-resistant (Bt) Cotton: Approximately $90\%$ of planted acres.

  • Insect-resistant (Bt) Corn: Approximately $85\%$ of planted acres.

Global Challenges Fostering GMO Development

• Human Population Growth:

  • The population exceeded 6 billion in 1999 and is currently just over 8 billion.

  • The annual growth rate is roughly $1.02\%$, adding 83 million people every year.

  • This creates a massive demand for food and biotechnology products like medicine.

• Climate Change:

  • Global warming alters ecosystems by changing temperature and shifting precipitation patterns.

  • Current data shows regions like the North Pole, Canada, Russia, and parts of the United States are seeing temperature increases of up to $4^{\circ}F$ compared to the 1981–2010 average.

• Pest Management:

  • Traditional chemical insecticides can lead to insecticide resistance.

  • Bt Crops: Plants engineered with a gene from the bacterium $Bacillus\,thuringiensis$ produce an endotoxin that kills insects but does not harm the plant or humans.

Examples of Genetically Modified Organisms

• Bacteria (First to be modified due to small genomes, presence of plasmids, and rapid generation time of every 15 minutes):

  • Biotechnology Products: Human insulin, Hepatitis B vaccines, Clotting factors for hemophilia, Human growth hormone, and Interferons for cancer.

  • Plant Protection: Proteins that prevent freezing or internal insect protection (Bt).

  • Bioremediation: Breaking down toxic chemicals, such as oil spills or mercury.

  • Chemical Synthesis: Production of biofuels and organic chemicals.

• Animals:

  • Disease Models: Mice, goats, or pigs with human genes for cancer or cystic fibrosis studies.

  • Pharming: Expressing pharmaceutical compounds in meat, milk, or eggs.

  • Nutritional Value: Increasing growth rates or improving meat/milk quality.

  • Xenotransplantation: Pigs engineered to provide organs (liver, kidney, bone marrow) for humans.

  • Pest Control: Engineering sterile insects to disrupt disease-carrying populations (e.g., mosquitoes).

• Plants (Released and Under Development):

  • Current (USA): Squash (disease resistance), Soybean/Corn (herbicide/insect/drought tolerance), Papaya (disease resistance), Potato (reduced bruising/acrylamide), Apples (non-browning), Rice (nutritional content).

  • Under Development: Beans (disease resistance), Eggplant (insect resistance), Sugarcane (drought tolerance), Wheat (herbicide/drought resistance).

Plant Biology and Life Cycles

• Basic Characteristics: Plants are multicellular eukaryotes and photosynthetic autotrophs.

• Evolutionary Groups:

  • Mosses: Primitive, lack transport tissue, live in moist environments.

  • Lycophytes: First with vascular tissue (xylem for water, phloem for nutrients); possess microphylls.

  • Ferns: Vascular plants with large leaves (megaphylls).

  • Gymnosperms: First to evolve seeds (embryo with a protective coat and nutrients).

  • Angiosperms: Possess flowers to attract pollinators and produce fruit.

• Alternation of Generations:

  • Sporophyte Phase ($2n$): Diploid; produces haploid spores via meiosis.

  • Gametophyte Phase ($n$): Haploid; produces haploid gametes (egg and sperm) via mitosis.

  • Zygote ($2n$): Formed when egg and sperm fuse.

• Angiosperm Lifecycle Details:

  • The sporophyte is the dominant generation (the visible plant/flower).

  • Pollination occurs when pollen grains (male gametophyte) from the anther are delivered to the female gametophyte (embryo sac) in the ovary.

  • Double Fertilization: One sperm fuses with the egg to form a zygote ($2n$); another fuses with two polar nuclei to create the endosperm ($3n$), which provides nutrition.

Photosynthesis: The Production Process

• Location: Occurs primarily in the mesophyll cells of leaves within organelles called chloroplasts.

• Internal Structure of Chloroplasts: Double-membrane outer layer, stroma (liquid center), and thylakoids (interconnected disc-like stacks called grana).

• The Chemical Pathway:

  • $CO_2 + H_2O + \text{solar energy} \rightarrow CH_2O + O_2$

• Two Stages:

  1. Light-dependent Reactions: Occur in the thylakoid. Capture solar energy to produce ATP and NADPH. Water is split, releasing Oxygen ($O_2$) as a byproduct.

  2. Light-independent Reactions (Calvin Cycle): Occur in the stroma. Use ATP, NADPH, and Carbon Dioxide ($CO_2$) to synthesize carbohydrates ($CH_2O$).

Improving Plants via Genetic Modification

• Fruit Ripening: In Arctic apples, the gene for polyphenol oxidase (PPO) is silenced. PPO normally facilitates the reaction between polyphenols and oxygen that causes browning.

• Crop Yield: Resistance to herbicides like glyphosate (RoundUp) allows farmers to kill weeds without harming crops.

• Nutritional Content (Golden Rice):

  • Rice was engineered to produce beta-carotene (a Vitamin A precursor) by adding two genes: one from a daffodil and one from a soil bacterium.

  • Targeted to reduce the estimated 600,000 annual deaths of children due to Vitamin A deficiency.

Molecular Basis: DNA and Gene Expression

• DNA Structure: A double helix with two anti-parallel strands (one 3' to 5', the other 5' to 3').

• Complementary Base Pairing: Adenine ($A$) pairs with Thymine ($T$) via two hydrogen bonds; Cytosine ($C$) pairs with Guanine ($G$) via three hydrogen bonds.

• Gene Expression:

  1. Transcription: In the nucleus, a DNA template strand is copied into messenger RNA (mRNA).

  2. Translation: In the cytoplasm (at the ribosome), mRNA codons are interpreted to build a polypeptide chain (protein).

• Enzymes: Proteins that act as catalysts. They have a specific three-dimensional shape with an "active site" that binds to a specific "substrate."

Biotechnology Techniques

• DNA Sequencing: Determining the exact order of nucleotides ($A, T, C, G$) using fluorescently labeled nucleotides and laser detection.

• DNA Probes: Single-stranded DNA with a fluorescent label used to find complementary sequences in a genome.

• DNA Microarrays (Gene Chips): Slides containing thousands of DNA segments used to screen for specific gene expressions.

• Gene Cloning:

  1. Restriction Enzymes cut DNA at specific sequences, creating "sticky ends."

  2. The gene of interest is inserted into a bacterial plasmid.

  3. DNA Ligase seals the DNA, creating recombinant DNA.

  4. Bacteria reproduce, copying the recombinant plasmid.

• Polymerase Chain Reaction (PCR):

  1. Denaturation ($95^{\circ}C$): Heat separates DNA strands.

  2. Annealing ($55^{\circ}C$): Primers bind to target sequences.

  3. Extension ($72^{\circ}C$): Taq DNA polymerase adds complementary bases.

• CRISPR-Cas9: A gene-editing tool that uses a guide RNA and the Cas9 enzyme to create double-strand breaks for gene inactivation or point mutations.

• Transformation Methods:

  • Agrobacterium tumefaciens: A bacterial vector that naturally inserts DNA into plant cells.

  • Particle Bombardment (Gene Gun): Firing gold or tungsten particles coated with DNA into plant tissue.

  • RNA Interference (RNAi): Inserting small RNA pieces complementary to mRNA. They bind to form double-stranded RNA, which the cell's RISC enzyme destroys, thus "silencing" the gene.

Risks and Future of GMOs

• Risks:

  • Gene Transfer: Resistance genes (e.g., glyphosate resistance) could transfer to wild weed species.

  • Human Allergies: In 2000, Cry9C protein (Bt) from non-food corn accidentally entered the food chain (taco shells), causing allergic reactions in sensitive individuals.

  • Non-target Species: Concerns that Bt toxins might harm beneficial insects, though studies are ongoing.

• Future Developments:

  • AquaAdvantage Salmon: Contains growth hormone genes from Chinook salmon and a promoter from ocean pout, allowing it to grow faster.

  • Malaria Prevention: Genetically modified fungi designed to eliminate mosquitoes.

  • Resilience: Developing crops that are both heat and drought-resistant to adapt to climate change.

Questions & Discussion

• Question 1: Which of the following best describes the scientific definition of a GMO?

  • Answer: c. Organisms in which the genetic material (DNA) has been altered in a way that does not occur naturally by mating and/or natural recombination.

• Question 2: This was the first GMO to be approved for human consumption.

  • Answer: a. Tomato.

• Question 3: Which was the first organism to have its DNA directly manipulated in the lab, and thus considered the first GMO?

  • Answer: d. Escherichia coli.

• Question 4: Bacillus thuringiensis (Bt) endotoxins are used in plants for which of the following reasons?

  • Answer: b. To provide protection against pest species.

• Question 5: Climate change has the ability to alter which characteristic of an ecosystem? Select all that apply.

  • Answer: a. Precipitation levels, c. Temperature.

• Question 6: Genetically modified plants may be produced for which of the following reasons?

  • Answer: e. All of the above (Drought resistance, herbicide resistance, insect resistance, reduced spoilage).

• Question 7: Which of the following are being genetically modified to produce biotechnology products such as vaccines, drugs, or other chemical products?

  • Answer: a. Bacteria, b. Plants, c. Animals.

• Question 8: The majority of crop plants, such as rice, soybeans, and corn, belong to this classification of plants.

  • Answer: c. Angiosperms.

• Question 9: Which of the following is not correct about the life cycle of plants?

  • Answer: b. Meiosis produces gametes in plants. (Note: Meiosis produces spores; gametes are produced by mitosis in the gametophyte).

• Question 10: Which of the following is not an input for photosynthesis?

  • Answer: d. Carbohydrates, e. Oxygen.

• Question 11: Which of the following is not correct regarding photosynthesis?

  • Answer: a. All of the reactions require sunlight. (Note: The Calvin Cycle is light-independent).

• Question 12: Golden rice is an example of a plant that has been modified to do which of the following?

  • Answer: c. Add nutritional content.

• Question 13: Why have Arctic apples been genetically modified?

  • Answer: c. To prevent over-ripening and spoiling of the fruit.

• Question 14: Which of the following are correct statements regarding the DNA molecule? Select all that apply.

  • Answer: a. Anti-parallel configuration, b. Information in nucleotides, c. Double helix.

• Question 15: The term gene expression refers to which of the following?

  • Answer: a. The processing of the genetic information to form a functional protein.

• Question 16: Select all of the following that can be used to make copies of a gene of interest.

  • Answer: a. Polymerase chain reaction, d. DNA cloning.

• Question 17: Select all of the following that are correct regarding DNA probes.

  • Answer: b. Complementary to the sequence of nucleotides, c. Used in DNA microarrays.

• Question 18: Select all of the following that allow geneticists to change a specific area of a gene.

  • Answer: a. PCR site-specific mutagenesis, c. CRISPR.

• Question 19: Which of the following does not introduce new genes into a plant to transform it?

  • Answer: b. RNA interference (Note: It uses RNA to silence existing genes).

• Question 20: Which of these statements are correct?

  • Answer: c. Resulted in gene transfer to weed species.

• Question 21: Future genetically modified plants and animals are being designed to meet what needs of society?

  • Answer: d. All of the above (Prevention of disease, food supply, climate change adaptation).