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
