Overview
This lecture explains the concepts of genetic diversity, heritability, and phenotypic variation in plants, focusing on how genetics and environment influence observable traits and their importance in breeding and selection.
Genetic and Phenotypic Diversity
- Phenotype is determined by both genetic factors (genotype) and environmental factors.
- Phenotypic diversity equals the sum of genetic diversity and environmental diversity.
- Traits mainly influenced by environment (e.g., flower color) are called environmentally determined.
- Genetic diversity arises from differences in genotypes and results in inheritable trait variations.
Measuring Genetic and Environmental Influence
- Quantitative traits (like yield, protein content) are influenced by multiple genes and the environment.
- Estimating the influence of genetics vs. environment is key for effective selection in breeding.
- Heritability is calculated as the ratio of genetic variance to total phenotypic variance.
Heritability: Concepts and Calculation
- Heritability (h²) = Genetic variance / Phenotypic variance.
- High heritability indicates traits largely determined by genetics; low heritability indicates strong environmental influence.
- Experimental designs (e.g., growing genetically identical plants in different environments) help estimate variance sources.
Selection and Response
- Selection means choosing individuals with desirable traits from a diverse population.
- Selection differential: difference between the mean of selected individuals and the initial population mean.
- Selection response: the difference between the next generation's mean and the original population mean after selection.
- The greater the initial diversity, the higher the potential response to selection.
Interpreting Heritability Values
- Heritability categories: low (0-0.25), medium (0.25-0.5), high (0.5-1).
- If heritability = 1, trait is entirely genetic; if 0, it’s entirely environmental.
- Heritability guides breeders in predicting selection effectiveness and justifying breeding costs.
Key Terms & Definitions
- Phenotype — observable traits of an organism.
- Genotype — genetic makeup of an organism.
- Genetic Diversity — variation in genes among individuals.
- Environmental Diversity — trait variation due to environmental conditions.
- Heritability (h²) — proportion of phenotypic variance attributable to genetic variance.
- Selection Differential — difference between selected individuals’ mean and original mean.
- Selection Response — improvement in trait mean in the next generation after selection.
Action Items / Next Steps
- Find a journal article (in English or Indonesian) about heritability and summarize it in less than one page.