Heritability and Environmental Variance
Interpret heritability as a population- and environment-specific variance ratio rather than a permanent percentage of genetic control.
Educational reference · evidence, sources, and limits shown below
Interpret heritability as a population- and environment-specific variance ratio rather than a permanent percentage of genetic control.
Terms to know
- Phenotypic variance
- Observed variation attributed to genetic, environmental, interaction, and residual components.
- Broad-sense heritability
- Proportion of phenotypic variance associated with all genetic differences in the studied population and design.
- Narrow-sense heritability
- Proportion associated with additive genetic variance relevant to response to selection.
- Repeatability
- Consistency of measurements or performance under defined repeat observations.
Core science
Heritability describes variation in a population under a particular design. Broad-sense heritability can include additive, dominance, and epistatic genetic variance; narrow-sense heritability focuses on transmissible additive variance. Neither number states what fraction of one plant’s trait was ’caused by genes.’
Changing environmental uniformity, population diversity, replication, or measurement error changes the variance components and therefore the estimate. A highly heritable flowering date can still change with photoperiod and temperature. A low estimate can reflect noisy measurements or a narrow genetic sample rather than absence of useful genetic differences.
Clonal replicates help estimate environmental and residual variation because ramets share a starting genotype. Seed families provide different relatedness structures. Both require randomization, blocking, adequate replication, and a statistical model that matches the design.
Why this matters in cultivation
- Selection intensity should follow estimate quality. Traits with weak repeatability need improved measurement and replicated testing before discarding genetics.
- Report prediction accuracy in a new generation or site. A high heritability estimate from the selection environment is not the same as validated gain under production conditions.
Measure and record
Population
Entries, relatedness, generations, sample size, missing data, and selection before trial.
Design
Sites, rooms, blocks, replicates, randomization, checks, and experimental unit.
Trait quality
Protocol, operator, instrument, technical repeats, repeatability, and outlier rule.
Variance model
Genetic, environment, GxE, block, residual components, assumptions, and uncertainty.
Selection response
Parental mean, offspring mean, selection differential, realized gain, and new-environment test.
Common misconceptions
Correction: It changes with population, environment, design, and measurement.
Correction: Environmental shifts can change the mean even when rank differences are genetic.
Correction: Ramets still differ through environment, pathogens, development, sampling, and mutation.
Evidence limits
Reliable cannabis heritability estimates remain trait-, germplasm-, and trial-specific. Estimates from fiber hemp, field trials, or one breeding population should not be transferred directly to indoor drug-type production.
Related encyclopedia topics
- THC-ENC-144, THC-ENC-146-147, THC-ENC-191-200, and THC-ENC-341-360.
Source notes
- Campbell B.J. et al. (2019). Genotype x environment interactions of industrial hemp cultivars. Agrosystems, Geosciences & Environment 2:1-11.
- Petit J. et al. (2020). Genetic variability of morphological, flowering, and biomass quality traits in hemp. Frontiers in Plant Science 11:102.
- Woods P. et al. (2021). Quantitative trait loci controlling agronomic and biochemical traits in Cannabis sativa. Genetics 219:iyab099.
- Stack G.M. et al. (2023). Correlations among morphological and biochemical traits in high-cannabinoid hemp. Plant Direct 7:e503.
This lesson summarizes the source material and its evidence limits for education. Use direct measurement, controlled comparison, and the cited sources when conditions differ or a decision carries meaningful risk.