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Ch. 20 - Quantitative Genetics and Multifactorial Traits
Klug - Essentials of Genetics 10th Edition
Klug10th EditionEssentials of GeneticsISBN: 9780135588789Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoKlug 10th EditionCh. 20 - Quantitative Genetics and Multifactorial TraitsProblema 15a
Capitolo 20, Problema 15a

A hypothetical study investigated the vitamin A content and the cholesterol content of eggs from a large population of chickens. The following variances (V) were calculated.

Calculate the narrow-sense heritability (h²) for both traits.

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Understand that narrow-sense heritability (h²) is the proportion of the total phenotypic variance (V_P) that is due to additive genetic variance (V_A). The formula is: \(h^{2} = \frac{V_{A}}{V_{P}}\).
Identify the values for each trait from the table: for Vitamin A, V_P = 125.5 and V_A = 12.0; for Cholesterol, V_P = 862.0 and V_A = 192.1.
Apply the formula for Vitamin A: substitute V_A = 12.0 and V_P = 125.5 into \(h^{2} = \frac{V_{A}}{V_{P}}\) to express the heritability calculation.
Apply the formula for Cholesterol: substitute V_A = 192.1 and V_P = 862.0 into \(h^{2} = \frac{V_{A}}{V_{P}}\) to express the heritability calculation.
Interpret the results by understanding that higher h² values indicate a greater proportion of phenotypic variance is due to additive genetic factors, which implies stronger potential for response to selection.

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Phenotypic Variance (V_P)

Phenotypic variance represents the total observed variation in a trait within a population. It includes genetic variance (additive, dominance, etc.) and environmental variance. Understanding V_P is essential because it forms the denominator in heritability calculations, reflecting all sources of variation affecting the trait.
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08:34
Analyzing Trait Variance

Additive Genetic Variance (V_A)

Additive genetic variance is the portion of genetic variance attributed to the additive effects of alleles. It is crucial for predicting response to selection because it reflects the heritable component passed from parents to offspring. Narrow-sense heritability is calculated using V_A relative to total phenotypic variance.
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Traits and Variance

Narrow-Sense Heritability (h²)

Narrow-sense heritability (h²) quantifies the proportion of phenotypic variance due to additive genetic variance (h² = V_A / V_P). It measures the potential for a trait to respond to selection and is key in breeding and evolutionary studies. Calculating h² requires knowledge of both V_A and V_P.
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Calculating Heritability
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In an assessment of learning in Drosophila, flies were trained to avoid certain olfactory cues. In one population, a mean of 8.5 trials was required. A subgroup of this parental population that was trained most quickly (mean=6.0) was interbred, and their progeny were examined. These flies demonstrated a mean training value of 7.5. Calculate realized heritability for olfactory learning in Drosophila.

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The mean and variance of plant height of two highly inbred strains (P₁ and P₂) and their progeny (F₁ and F₂) are shown here.


  Strain  Mean (cm)  Variance 

   P₁     34.2        4.2

   P₂     55.3        3.8

   F₁     44.2        5.6

   F₂     46.3       10.3


Calculate the broad-sense heritability (H²) of plant height in this species.

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Domanda del libro di testo

The following variances were calculated for two traits in a herd of hogs.

Calculate broad-sense (H²) and narrow-sense (h²) heritabilities for each trait in this herd.

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A hypothetical study investigated the vitamin A content and the cholesterol content of eggs from a large population of chickens. The following variances (V) were calculated.

Which trait, if either, is likely to respond to selection?

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In a herd of dairy cows the narrow-sense heritability for milk protein content is 0.76, and for milk butterfat it is 0.82. The correlation coefficient between milk protein content and butterfat is 0.91. If the farmer selects for cows producing more butterfat in their milk, what will be the most likely effect on milk protein content in the next generation?

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The following variances were calculated for two traits in a herd of hogs.

Which of the two traits will respond best to selection by a breeder? Why?

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