Plant Breeding and Genetics
Plant Breeding
Ability to create new plant varieties by crossing different plants.
Traditional plant breeding involves making crosses, collecting seeds, and evaluating plants.
Traditional Plant Breeding
Cross plants with desirable characteristics to obtain new traits.
Growth from many seeds increases chances of successful traits.
Plants sorted based on desired characteristics; select the best for further breeding.
Example: Cross red and white flowers to obtain pink flowers.
Mutation Breeding
A method to introduce traits not available in the original population (e.g., fragrance, disease resistance).
Uses X-rays or chemical mutagens (like ethyl methyl sulfonate) to alter DNA.
Can lead to beneficial mutation (good chimaeras) or harmful traits (deleterious traits).
Modern Breeding Techniques
Breeding at the gene level allows faster identification and incorporation of specific traits (e.g., drought tolerance).
Techniques include recombinant DNA and protoplast fusion.
First attempts at gene insertion involved using gold particles to deliver DNA to plant cells.
Genetics Terminology
Chromosomes: DNA sequenced and packaged in units within cell nuclei.
Genes: Functional hereditary units located on chromosomes; Plural: loci.
Alleles: Variants of a gene, often represented by letters (e.g., capital for dominant, lowercase for recessive).
Diploid: Organisms with two sets of chromosomes; Polyploid: Organisms with multiple sets (e.g., triploids, tetraploids).
Importance of Triploids
Triploids are often sterile, preventing unwanted seed production (e.g., seedless watermelons, bananas).
Used in ornamental plants to control invasiveness (e.g., Buddleja varieties).
Genotype vs. Phenotype
Genotype: Genetic makeup of an organism (e.g., AA, Aa, aa).
Phenotype: Observable traits (e.g., tall plant, red flowers).
Dominance Patterns
Complete Dominance
Dominant alleles mask recessive alleles (e.g., AA and Aa are phenotypically the same).
Two phenotypes: dominant and recessive.
Incomplete Dominance
Heterozygous individuals express an intermediate trait (e.g., red + white = pink).
Gregor Mendel's Discoveries
Established the principles of inheritance using pea plants.
Discovered dominance and recessive traits, and the law of independent assortment.
Used mathematical models (chi-square method) to analyze genetic ratios and validate his hypothesis.
Chi-Square Method
Formula:
Used to determine if the observed data fit the expected genetic ratios.
Key for validating hypotheses in genetics.