Flashcards in Genetic Technology in Agriculture (Chapter 19) Deck (39)
What proteins for use in medicine are produced from GM plants?
- Vaccines, albumin, proteins in breast milk for infants
- Avoids problems of contamination by animal proteins
What are most GM plants?
- Crop plants modified to be herbicide or insect resistant to increase crop yield
- Some provide improved nutrition
What is oil seed rape?
A source of of vegetable oil used as biodiesel fuel, as a lubricant and in human/animal foods
How has oil seed rape been modified to make it more desirable?
- Natural oil seed rape contains substance (erucic acid and glucosinolates) which are undesirable in oil used in human/ animal foods
- Hybrid called canola produces a low conc of these substances
How has gene tech modified oil seed rape to improve its yield?
- Gene tech has been used to produce herbicide resistant strains of oil seed rape resistant to glyphosate or glufosinate
- This allows fields to be sprayed with herbicide after the crop has germinated, killing any weeds that would compete with the crop for space, light, water or ions
What are the two common herbicides?
Glyphosate and glufosinate
How does glyphosate work?
1) it inhibits an enzyme involved in the synthesis of 3 amino acids: phenylalanine, tyrosine and tryptophan
2) it is absorbed by the plant's leaves and transported to the growing tips
3) the amino acids are needed for producing essential proteins ∴ the plant dies
How can microorganisms be used to genetically engineer herbicide resistant crops?
- Some microorganisms e.g. Agrobacterium have versions of the enzyme that are not affected by glyphosate
- ∴ the gene for this enzyme can be transferred into crop plants
What two herbicides has tobacco been made resistant to?
Sulfenylurea and dinitroaniline by taking genes from another species of plant
What are the possible negative environmental effects of growing herbicide-resistant crops?
1) GM plant will become an agricultural weed
2) pollen will transfer the gene to wild relatives, producing hybrid offspring that are invasive weeds
3) herbicide-resistant weeds will evolve bc so much of the same herbicide is used
Is GM oil seed rape more or less invasive than unmodified versions?
Slightly less invasive
How is the risk of pollen transfer shown in oil seed rape and how can this be prevented?
- Oil seed rape interbreeds easily with 2 related species (wild radish/turnip)
- Flowers can be pollinated by wind
- it has been shown that resistance can be passed down through hybrid offspring (only in labs)
- ∴ safe planting distances are needed to allow organic farming to remain GM-free
Discuss the risk of herbicide resistant weeds arising
- Near where glyphosate has been much use, herbicide resistant mutant plants of various species have been found
- However, herbicide is not only used on resistant crop species
- Also, GM is not directly responsible as resistance may evolve in the absence of any GM crop
Give two examples of how crops made insect-resistant have increased the yield of the crops
1) maize is protected against the corn borer, which eats the leaves of the plants and burrows into the stalk, eating its way upwards until the plant cannot support the ear
2) cotton is protected against pests e.g. boll weevil
What insect is GM tobacco (not yet grown commercially) protected against?
Tobacco bud worm
What are the 4 possible negative environmental effects of growing insect-resistant crops?
1) evolution of resistance by insect pests
2) damaging effect on other species of insect
3) transfer of the added gene to other species of plant
4) where lots of GM crop is grown, there is a danger of losing biodiversity
How are negative environmental effects minimised when growing insect-resistant crops?
- Less pesticide is used ∴ reducing the risk of spray carrying to and affecting non-target species of insects in other areas
- Only insects that eat the crops are affected
Describe how Bt toxin has been used to make GM insect-resistant crops e.g. Bt maize
- A gene for Bt toxin, which is lethal to insects that eat it but harmless to other animals has been taken from the bacterium Bacillus thuringiensis
- Different strains of the bacterium produce different toxins that can be used against different insect species
- Crop plants containing the Bt toxin ∴ produce their own insecticide
What is the risk of using Bt toxin to GM plants?
- Insect populations can evolve resistance to toxins
- Large numbers of crop plants containing the Bt toxin genes may accelerate the evolution of resistance to it
- e.g. many populations of corn borers in USA are resistant to Bt toxin (but resistance = recessive allele)
Discuss the potential environmental risks of using the Bt toxin
1) pollen of Bt maize expresses the gene and can disperse at least 60m by wind, transferring to milkweed, a source of food for caterpillars of the monarch butterfly (reduces survival rate of caterpillars to 56% in lab) - however doesn't reflect real world bc caterpillars are not normally present when pollen is shed
2) leaves from GM Bt plants can end up in streams and be eaten by aquatic insect larvae e.g. caddis larvae, reducing the growth of the larvae
3) if Bt maize is grown in Mexico, could pollinate teosinte (wild parent species), transferring genes to it - but maize pollen not viable after 2 hours of being released from anthers and exposed to air ∴ need 2 hour wind drift distance
4) some evidence of reduced populations of microorganisms in soil where Bt maize has been growing
What is a social disadvantage of growing GM crop?
GM crop seed is expensive and have to buy new seed each season ∴ cost may outweigh the advantage of herbicide of insect resistance
Why is vitamin A (VA) deficiency a problem?
- Can cause blindness (WHO estimate: 500,000 children go blind every year as a result of VA deficiency)
- Can cause immunodeficiency syndrome, which is a significant cause of mortality esp in children in certain parts of the world
Where is VA deficiency a problem?
Where people are poor and rice forms a major part of their diet
What is vitamin A?
A fat soluble vitamin found in oil fish and animal products (eggs, milk, cheese) and made from carotene, found in carrots
Where are pro-VA carotenoids found in rice?
In the aleurone layer of rice grains, but not in the endosperm which is what humans eat
Why is white rice produced instead of brown rice?
Bc it no longer contains the aleurone layer (unlike brown rice), which goes rancid if stored for any length of time
Why can it be difficult for poor families to avoid VA-deficiency?
Due to the lack of animal products and not enough carotenoid containing vegetables
How is Golden Rice produced?
1) genes for the production of carotene are extracted from maize and the bacterium Pantonoea ananatis
2) these genes and promoters are inserted into plasmids, which are inserted into bacteria (Agrobacterium tumefaciens) - these bacteria naturally infect plants ∴ can introduce the GM plasmids into rice cells
3) the bacteria are mixed with rice embryos in petri dishes, some of which were infected by the bacteria containing the carotene genes
4) the rice embryos containing the carotene genes were grown into adult plants, producing seeds containing carotene in their endosperm
Why is Golden rice called so?
Because of the high conc of carotene, an orange pigment