Q36 - Broad- vs Narrow-Sense Heritability and a Bean Seed-Weight Calculation

Theoretical A Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Quantitative Genetics, Heritability & Inbreeding

Heritability in broad sense (H2) is the ratio of total genetic variance (Vg) to total phenotypic variance (Vp): H2 = Vg/Vp. The phenotypic variance is often divided into three components: the genetic variance (Vg), environmental variance (Ve) and the interaction variance (Vi), Vp = Vg + Ve + Vi. The genetic variance is divided into three components: the additive genetic variance (Va, cumulative effects of individual loci), the dominant genetic variance (Vd), and the genetic interaction variance (Vgi), Vg = Va + Vd + Vgi. Heritability in narrow sense (h2) = Va/Vp.

Using the information and data, determine which of the statements are true or which are false.

A. A low H2 value of a trait always indicates that the trait is determined mainly by the environment.

B. Genetic variance depends on the environment to which the population is exposed.

C. The artificial selection for a trait with higher h2 is more successful than that for a trait with lower h2.

D. Two pure strains of bean that produce seeds with different weights were crossed. The variances of seeds (Vp) from F1 and F2 plants are 2.0 and 4.1, respectively. If we ignore interaction effects, H2 of seeds is 0.51.

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Question reproduced from IBO 2016, Theoretical Paper A, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)