Talk:Heritability
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Page scope
Heritability covers heritability as a concept: the division of the variance of a trait into genetic and environmental parts, broad- and narrow-sense heritability, how each is estimated from clones, replicated field trials, families of seed and sets of populations, how an estimate is read, and the estimates published for cannabis. The heritable characters themselves, trait by trait, belong to Genetic traits. The response of one genotype to different growing conditions belongs to Phenotypic plasticity, and the use of heritability in choosing parents by their own phenotype to Mass selection.
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Discussion
Sources
- Beavis and colleagues (2023), in Suza and Lamkey (eds), Quantitative Genetics for Plant Breeding, chapter 6, "Components of Variance": the partition of the phenotypic variance, the additive, dominance and epistatic parts of the genotypic variance, and Lush's broad- and narrow-sense heritability (1937).
- Beavis and colleagues (2023), same book, chapter 9, "Selection Response": heritability on an entry-mean basis, Hanson's definition of 1963, the reference population, environments and units a reported heritability should name, half-sib families, realised heritability, restricted maximum likelihood and the breeder's equation.
- Felsenstein (2019), Theoretical Evolutionary Genetics, chapter IX: covariances between relatives, the regression of offspring on the mean of the parents, three methods of estimation, common environments, genotype-by-environment interaction and sample size (pp. 429–438); Fisher (1918) and Wright (1921) (p. 439).
- Hennink (1994), Euphytica 78: 69–76: 252 fibre hemp plants scored in 1991 and their progenies grown as half-sib families in 1992; heritability of bast fibre content high; mass selection effective for bast fibre and able to reduce THC.
- Naim-Feil and colleagues (2021), BMC Plant Biology 21: 294: broad-sense heritability of nine physiological and phenological traits and of weekly plant height and stem diameter in 121 medicinal cannabis genotypes grown as clones; a narrow-sense estimate of 0.22 for stem diameter in hemp, cited from Hennink (1994).
- Naim-Feil and colleagues (2023), Plants 12: 493: broad-sense heritability of cannabinoids, phenology, plant morphology and inflorescence traits in 119 medicinal cannabis genotypes grown as clones.
- Petit and colleagues (2020), Frontiers in Plant Science 11: 102: variance components and entry-mean heritability of 28 traits in 123 hemp accessions at three sites in Europe (their Table 7).
- Babaei and colleagues (2024), BMC Plant Biology 24: 151: broad-sense heritability of phenological and morphological traits across 25 landrace populations of Iran, for female and male plants separately.
Where the sources disagree
- Two broad-sense ratios. Lush's broad-sense heritability is the genotypic variance over the phenotypic variance of single plants. The ratio on an entry-mean basis, which Petit and colleagues report, divides the interaction and error variances by the numbers of environments and plots, so it rises as they are added. Beavis and colleagues treat the second as similar to Lush's but not the same concept.
- Narrow-sense heritability of half-sib families. Beavis and colleagues note that an estimate from half-sib families, on an entry-mean basis, is a narrow-sense heritability for that population of half-sibs and differs from Lush's original definition.
The narrow-sense estimate for stem diameter
The figure of 0.22 comes from Naim-Feil and colleagues (2021), who cite Hennink (1994) for it.
Terms
- Broad-sense heritability (H2): the genotypic variance over the phenotypic variance.
- Narrow-sense heritability (h2): the additive variance over the phenotypic variance; the slope of the regression of offspring on the mean of their parents.
- Entry-mean basis: the variance of the means of entries (accessions, families or cultivars) over their plots and environments, used as the denominator in place of the variance among single plants.
- Realised heritability: the response to selection divided by the selection differential, measured after a round of selection.
- Among populations: in Babaei and colleagues (2024) the genotypes compared were the 25 populations, each grown from seed, and the estimates describe differences among them.
Images reserved in the article
Three images have places in the article but are not yet uploaded:
File:Cannabis-clonal-trial-medicinal-genotypes.jpg(lead): a photograph of the medicinal cannabis genotypes grown as clones in the controlled-environment facility of Naim-Feil and colleagues (2021). Panel A of their Figure 6, "Plant development in the controlled environment facility", shows it; the article is published under the CC BY 4.0 licence.File:Cannabis-heritability-midparent-regression.jpg(Genetic and environmental variance), a diagram to be drawn: a scatter of family points with the mean of the two parents on the horizontal axis and the mean of their offspring on the vertical axis, both as deviations from the population mean; a fitted line through the origin with its slope labelled h2; a dashed diagonal of slope 1 for comparison. No numbers, trait or crop names.File:Cannabis-heritability-estimate-designs.jpg(How heritability is estimated), a diagram to be drawn in three panels: one stock plant and five identical cuttings, labelled "Clones: broad sense"; plots of one accession at three sites, labelled "Accessions over sites: entry-mean basis"; two parent plants joined to a row of their seedlings, labelled "Parents and offspring: narrow sense". No numbers.