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Chapter 21: Problem 9

Define the term broad-sense heritability (H2). What is implied by a relatively high value of \(H 2 ?\) Express aspects of broad-sense heritability in equation form.

Short Answer

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Answer: Broad-sense heritability (H2) is a measure of the proportion of phenotypic variance in a population that can be attributed to genetic differences among individuals. It reflects the overall contribution of genetic factors to the observed variation in a given trait or characteristic. A high H2 value implies that genetic factors play a significant role in the phenotypic differences observed among individuals for the trait being studied, indicating that the trait may be more amenable to genetic interventions, such as selective breeding or gene therapy, to improve the trait or suppress undesired attributes.

Step by step solution

01

Define broad-sense heritability (H2)

Broad-sense heritability (H2) is a measure of the proportion of phenotypic variance in a population that can be attributed to genetic differences among individuals. It reflects the overall contribution of genetic factors to the observed variation in a given trait or characteristic, such as height, weight, or intelligence.
02

Implications of a high H2 value

A relatively high value of H2 implies that genetic factors play a significant role in the phenotypic differences observed among individuals for the trait being studied. This would mean that much of the observed variation in the population can be explained by genetic differences rather than environmental factors or measurement errors. Consequently, a high H2 value suggests that the trait may be more amenable to genetic interventions, such as selective breeding or gene therapy, to improve the trait or suppress undesired attributes.
03

Express aspects of broad-sense heritability in equation form

In equation form, broad-sense heritability (H2) can be expressed as: $$H^2 = \frac{V_G}{V_P}$$ where \(V_G\) represents the genetic variance (variation in the population due to genetic differences among individuals) and \(V_P\) represents the phenotypic variance (total variation in the population for the trait being studied, including genetic and environmental factors).

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Most popular questions from this chapter

Define the following: (a) polygenic, (b) additive alleles, (c) monozygotic and dizygotic twins, (d) heritability, and (e) QTL.

If one is attempting to determine the influence of genes or the environment on phenotypic variation, inbred strains with individuals of a relatively homogeneous or constant genetic background are often used. Variation observed between different inbred strains reared in a constant or homogeneous environment would likely be caused by genetic factors. What would be the source of variation observed among members of the same inbred strain reared under varying environmental conditions?

Height in humans depends on the additive action of genes. Assume that this trait is controlled by the four loci \(R, S, T,\) and \(U\) and that environmental effects are negligible. Instead of additive versus nonadditive alleles, assume that additive and partially additive alleles exist. Additive alleles contribute two units, and partially additive alleles contribute one unit to height. (a) Can two individuals of moderate height produce offspring that are much taller or shorter than either parent? If so, how? (b) If an individual with the minimum height specified by these genes marries an individual of intermediate or moderate height, will any of their children be taller than the tall parent? Why or why not?

A dark-red strain and a white strain of wheat are crossed and produce an intermediate, medium-red \(\mathrm{F}_{1}\). When the \(\mathrm{F}_{1}\) plants are interbred, an \(\mathrm{F}_{2}\) generation is produced in a ratio of 1 darkred: 4 medium-dark-red: 6 medium-red: 4 light-red: 1 white. Further crosses reveal that the dark-red and white \(\mathrm{F}_{2}\) plants are true breeding. (a) Based on the ratios in the \(\mathrm{F}_{2}\) population, how many genes are involved in the production of color? (b) How many additive alleles are needed to produce each possible phenotype? (c) Assign symbols to these alleles and list possible genotypes that give rise to the medium-red and light-red phenotypes. (d) Predict the outcome of the \(\mathrm{F}_{1}\) and \(\mathrm{F}_{2}\) generations in a cross between a true-breeding medium-red plant and a white plant.

Erma and Harvey were a compatible barnyard pair, but a curious sight. Harvey's tail was only \(6 \mathrm{cm}\) long, while Erma's was \(30 \mathrm{cm}\) Their \(F_{1}\) piglet offspring all grew tails that were \(18 \mathrm{cm} .\) When inbred, an \(\mathrm{F}_{2}\) generation resulted in many piglets (Erma and Harvey's grandpigs), whose tails ranged in 4 -cm intervals from 6 to \(30 \mathrm{cm}(6,10,14,18,22,26, \text { and } 30) .\) Most had 18 -cm tails, while \(1 / 64\) had 6 -cm tails and \(1 / 64\) had 30 -cm tails. (a) Explain how these tail lengths were inherited by describing the mode of inheritance, indicating how many gene pairs were at work, and designating the genotypes of Harvey, Erma, and their 18 -cm-tail offspring. (b) If one of the 18 -cm \(\mathrm{F}_{1}\) pigs is mated with one of the 6 -cm \(\mathrm{F}_{2}\) pigs, what phenotypic ratio would be predicted if many offspring resulted? Diagram the cross.
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