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Chapter 24: Problem 10

How do broad-sense and narrow-sense heritabilities differ???

Short Answer

Expert verified
Broad-sense heritability includes all genetic variances while narrow-sense includes only additive genetic variance.

Step by step solution

01

Understanding Heritability

Heritability is a measure of how much of a trait's variation is due to genetic factors as opposed to environmental factors. Heritability values range from 0 to 1, where 0 means no genetic contribution and 1 means exclusively genetic contribution.
02

Defining Broad-sense Heritability (H^2)

Broad-sense heritability, denoted as \( H^2 \), includes all genetic variance, which includes additive, dominance, and epistatic variances. It is calculated as the ratio of total genetic variance to the total phenotypic variance.\[ H^2 = \frac{V_{G}}{V_{P}} \]where \( V_{G} \) is the genetic variance and \( V_{P} \) is the phenotypic variance.
03

Defining Narrow-sense Heritability (h^2)

Narrow-sense heritability, denoted as \( h^2 \), only includes the additive genetic variance. It is calculated as the ratio of additive genetic variance to the total phenotypic variance.\[ h^2 = \frac{V_{A}}{V_{P}} \]where \( V_{A} \) is the additive genetic variance and \( V_{P} \) is the phenotypic variance.
04

Key Differences

The main difference is that broad-sense heritability considers all types of genetic variance while narrow-sense heritability considers only additive genetic variance, which is most relevant for predictions in selective breeding.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Understanding Broad-sense Heritability
Broad-sense heritability, represented as \( H^2 \), is a comprehensive measure used in genetics. It looks at how much of the variation in a trait is due to genetic factors, rather than environmental influences. This concept is useful when you want to consider all types of genetic effects contributing to trait variation. These effects include:
  • Additive variance 鈥� simple addition of genetic effects
  • Dominance variance 鈥� interactions between alleles at a locus
  • Epistatic variance 鈥� interactions between genes at different loci
The formula to calculate broad-sense heritability is \( H^2 = \frac{V_{G}}{V_{P}} \) where:
  • \( V_{G} \) is the total genetic variance
  • \( V_{P} \) is the total phenotypic variance
The value of \( H^2 \) ranges from 0 to 1. A value close to 1 indicates that the trait is mostly controlled by genetic factors.
Understanding Narrow-sense Heritability
Narrow-sense heritability, or \( h^2 \), is a more focused measure that considers only the additive genetic variance in trait variation. Additive genetic variance is crucial in predicting the response to selection in breeding programs, as it's the part of genetic variance that responds to selection and breeding decisions. This is why \( h^2 \) is very important for selective breeding.The formula to calculate narrow-sense heritability is:\[ h^2 = \frac{V_{A}}{V_{P}} \]where:
  • \( V_{A} \) is the additive genetic variance
  • \( V_{P} \) is the phenotypic variance
A high \( h^2 \) value indicates that selection based on this trait will likely result in significant improvements in future generations.
Exploring Genetic Variance
Genetic variance represents the diversity observed in a trait due to genetic differences among individuals in a population. This variance is the sum of different components, contributing to the total genetic variance, \( V_{G} \), which can be classified as:
  • Additive variance (\( V_{A} \)) 鈥� sum of average effects of individual alleles
  • Dominance variance 鈥� effects from interactions between alleles at the same gene
  • Epistatic variance 鈥� effects from interactions between multiple genes
Understanding genetic variance is key to grasping concepts like heritability, as it helps in identifying how much of the trait variation is attributed to genetic factors versus other influences.
Clarifying Phenotypic Variance
Phenotypic variance, denoted as \( V_{P} \), is the observed variation in a trait across a population. It is influenced by both genetic and environmental factors. To understand phenotypic variance, knowing its composition is crucial:
  • Genetic variance (\( V_{G} \)) 鈥� contributes to the hereditary portion of the variance
  • Environmental variance (\( V_{E} \)) 鈥� accounts for variation due to different environmental influences
Simply put, phenotypic variance gives a complete picture of all the factors influencing a trait. It serves as the denominator in both broad-sense and narrow-sense heritability formulas, highlighting its role in distinguishing genetic influences from environmental ones.

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Most popular questions from this chapter

Joe is breeding cockroaches in his dorm room. He finds that the average wing length in his population of cockroaches is 4 \(\mathrm{cm} .\) He chooses the six cockroaches that have the largest wings; the average wing length among these selected cockroaches is \(10 \mathrm{~cm}\). Joe interbreeds these selected cockroaches. From earlier studies, he knows that the narrow- sense heritability for wing length in his population of cockroaches is \(0.6 .\) a. Calculate the selection differential and expected response to selection for wing length in these cockroaches. b. What should be the average wing length of the progeny of the selected cockroaches?

Body weight and length were measured on six mosquito fish; these measurements are given in the following table. Calculate the correlation coefficient for weight and length in these fish. $$ \begin{array}{ccc} \text { Wet weight (g) } & \text { Length (mm) } \\ \hline 115 & 18 \\ \hline 130 & 19 \\ \hline 210 & 22 \\ \hline 110 & 17 \\ \hline 140 & 20 \\ \hline 185 & 21 \end{array} $$

A genetics researcher determines that the broad-sense heritability of height among Southwestern University undergraduate students is \(0.90 .\) Which of the following conclusions would be reasonable? Explain your answer. a. Sally is a Southwestern University undergraduate student, so \(10 \%\) of her height is determined by nongenetic factors. b. Ninety percent of variation in height among all undergraduate students in the United States is due to genetic differences. c. Ninety percent of the height of Southwestern University undergraduate students is determined by genes. d. Ten percent of the variation in height among Southwestern University undergraduate students is determined by variation in nongenetic factors. e. Because the heritability of height among Southwestern University undergraduate students is so high, any change in the students' environment will have minimal effect on their height.

Many researchers have estimated the heritability of human traits by comparing the correlation coefficients of monozygotic and dizygotic twins (see pp. \(747-748\) ). One of the assumptions made in using this method is that monozygotic twin pairs experience environments that are no more similar to each other than those experienced by dizygotic twin pairs. How might this assumption be violated? Give some specific examples of how the environments of two monozygotic twins might be more similar than the environments of two dizygotic twins.

The fitness of a genotype is its reproductive success relative to other genotypes in a population (see Chapter 25). If the fitnesses of all genotypes in a population were the same, what would be the response to selection?
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