Lecture 2: Plant Genetics and GMO Flashcards
Breeding Strategies
- Collect sources of genetic variation:
-Native varieties
-Weedy relatives
-Cultivars
-Landraces - Determine parent materials
- Hybridizaiton leads to new genetic combinations
- Selection of desired combination of traits
- Evaluation trials
- New variety
- Distribution to growers
Seed improvement technique: Selective breeding
-10,000 years ago
- Combining traits from similar and dissimilar plants by crossing into one genetic background with improved traits
Eg: Almost everything we eat (corn, cabbage)
Seed improvement technique: Interspecies Crosses
-Late 1800s
-Breeding and tissue culture techniques that permit genetic exchange between plants not crossing naturally
Eg: Pluots, tangelos, rice, wheat, some apples
Seed improvement technique: Mutagenesis
-1930s
-Using chemicals or radiation on seeds to change DNA and occasionally induce a favourable trait.
Eg: pears, apples, rice, yams, mints, some bananas
Seed improvement technique: Transgenesis (GMOs)
-1990s
-Adding a specific, well-characterised gene to a new seed to transfer a specific trait
Eg: Alfalfa, canola, corn, cotton, papaya, sweet potatoes, soybeans, sugar beets.
Pros of Genetic Engineering of Plants
- Biological resistance to pests and diseases: eliminates the need for insecticides that negatively impact environment
- Tolerance to herbicides: Roundup Ready technology promotes conservation tillage as it can be applied multiple times to the crop.
- Adaptation to environmental stresses: e.g resistance to high soil salinity
- Desirable functional characteristics: e.g. tomatoes have a longer shelf life
- Desirable nutritional characteristics: e.g. Golden rice has a high concentration of beta-carotene in its grain.
Cons of Genetic Engineering of Plants
- Overall safety of GMOs and genetic engineering
- Impact on human health: long term impact of transgenic plant consumption unknown
- Ability for genetically engineered plants to outcross with weedy relatives: possibility that they might become difficult to control
- Unintended effects on non target organisms: e.g. a possible negative effect on beneficial insects of some proteins like that introduced in Bt corn)
- Development of insects and weeds that are resistant to Bt or glyphosate: respectively resulting from overuse of the technology.
- Ethical and religious issues: related to genetic engineering and ownership of genes introduced in GMOs. Technology fee for transgenic seeds (more expensive). Illegal to reuse seeds from harvested, GMOs (have to repurchase).
Plastid DNA
-Double-stranded DNA molecule
-Multiple copies of the genome (up to 100 in mature cells)
-Genes involved in protein synthesis+photosynthesis
Polyploidy
(In general, number of chromosomes per nucleus varies)
-Plant species with more than two sets of chromosomes are called polyploids
-May arise in two ways:
AUTOPOLYPLOIDY: the entire chromosome set of a diploid plant is doubled
ALLOPOLYPLOIDY: the genomes of two (or more) different species are combined into a single new species interspecific hybridisation events.
Crop domestication
-Altering plants genetically to cope with our needs: continuous evolutionary process
Plant breeding
accelerated evolution guided by humans rather than nature enlargement of plant genetic diversity
-plant populations are genetically diverse and could be improved gradually across generations
Objectives of plant breeding
-Improved yield
-Disease resistance
-Pest resistance
-Stress tolerance
-Improved quality
Breeding Methods (BM)
- BM using sexually compatible germplasm
- BM using sexually incompatible germplasm
BM using sexually compatible germplasm
Self-pollinating or inbreeding highly homozygous, poor variability, significant amount of inbreeding wheat, rice, peas, beans, tomatoes and peppers, peaches
Self pollinating or Inbreeding:
-A breeder can make artificial crosses between self-pollinating plants
-Creation of hybrid populations: highly diverse groups of offsprings are created
-Cross-pollinating highly heterozygous corn, rye, alfalfa, clover, most fruits, nuts and vegetables
Inbreeding depression
Self pollination of cross-pollinated plants:
-small size, poor vigour, low reproductive capacity and abnormal plants due to recessive alleles
-Forcing self-pollination for several generations inbred lines with deleterious alleles eliminated
BM using sexually incompatible germplasm
-Species boundaries no longer exist
-Techniques: Gene splicing (transgenic plants), where genes from virtually any organism (viruses, humans) can be inserted into transgenic plants
How are transgenic plants made?
1. Find the insect resistance gene in the bacterium
2. Restriction enzymes cut the bacterial chromosome on both sides of the gene (not within the DNA sequence)
- The bacterial DNA and a cloning vector are cut with the same restriction enzyme
-Cloning vector: a piece of DNA that can copy itself in a living cell after transfer
-If cut bacterial DNA is mixed with cut plasmids, their sticky ends will join and create recombinant DNA.
- Recombinant DNA is a plasmid with an insect resistance gene attached to it. Insect resistance gene cloned.
- Insertion into plant cells through transformation:
-Plant cells will not take up foreign DNA
-Several techniques to transform plants
-Agrobacterium tumefaciens
How to incorporate desirable traits into plant genome
-Traditional approach: Plant breeding
-Plant genetic transformation and GMO
Examples of genetic manipulation: applications:
-herbicide tolerance
-herbicides: weed killers, used when the crop is not vulnerable itself
-glyphosate (RoundUp) broad-spectrum herbicide: effective against 76 of the world’s worst 78 weeds.
-biofortified food (Golden Rice)
