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Ch. 19 - Genetic Analysis of Quantitative Traits
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 19 - Genetic Analysis of Quantitative TraitsProblem 24a
Chapter 19, Problem 24a

Cattle breeders would like to improve the protein content and butterfat content of milk produced by a herd of cows. Narrow sense heritability values are 0.60 for protein content and 0.80 for butterfat content. The average percentages of these traits in the herd and the percentages of the traits in cows selected for breeding are as follows. Trait Herd Average Selected Cows Protein content 20.2% 22.7% Butterfat content  6.5%  7.4% Determine the selection differential (S) for each trait in this herd.

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Step 1: Understand the concept of selection differential (S). Selection differential is the difference between the average value of a trait in the selected individuals (breeding cows) and the average value of the trait in the population (herd average). It is calculated using the formula: S = X_selected - X_population, where X_selected is the trait value in selected individuals and X_population is the trait value in the population.
Step 2: Identify the given values for protein content. The herd average (X_population) for protein content is 20.2%, and the average for selected cows (X_selected) is 22.7%.
Step 3: Apply the formula for selection differential to protein content. Substitute the values into the formula: S_protein = X_selected_protein - X_population_protein. Use MathML to represent this: S=Xselected-Xpopulation.
Step 4: Identify the given values for butterfat content. The herd average (X_population) for butterfat content is 6.5%, and the average for selected cows (X_selected) is 7.4%.
Step 5: Apply the formula for selection differential to butterfat content. Substitute the values into the formula: S_butterfat = X_selected_butterfat - X_population_butterfat. Use MathML to represent this: S=Xselected-Xpopulation.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Narrow Sense Heritability (h²)

Narrow sense heritability (h²) is a measure of the proportion of phenotypic variance in a trait that can be attributed to additive genetic variance. It is crucial for predicting the response to selection in breeding programs, as it indicates how much of the trait's variation is heritable. Higher h² values suggest that selection will be more effective in improving the trait in future generations.
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Calculating Heritability

Selection Differential (S)

The selection differential (S) is the difference between the mean phenotype of the selected individuals and the mean phenotype of the entire population. It quantifies the extent to which selected individuals differ from the average, providing insight into the potential for genetic improvement. A larger selection differential indicates a stronger selection pressure, which can lead to greater changes in the trait over generations.
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Response to Selection (R)

Response to selection (R) refers to the expected change in the mean phenotype of a trait in the next generation as a result of selection. It can be calculated using the formula R = h² × S, where h² is the narrow sense heritability and S is the selection differential. Understanding R helps breeders anticipate the effectiveness of their selection strategies in achieving desired improvements in traits such as milk protein and butterfat content.
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Related Practice
Textbook Question

Suppose a polygenic system for producing color in kernels of a grain is controlled by three additive genes, G, M, and T. There are two alleles of each gene, G₁ and G₂, M₁ and M₂, and T₁ and T₂. The phenotypic effects of the three genotypes of the G gene are G₁G₁ = 6 units of color, G₁G₂ = 3 units of color, and G₂G₂ = 1 unit of color. The phenotypic effects for genes M and T are similar, giving the phenotype of a plant with the genotype G₁G₁M₁M₁T₁T₁ a total of 18 units of color and a plant with the genotype G₂G₂M₂M₂T₂T₂ a total of 3 units of color.

Assuming the threshold model applies to this kernel-color system, what proportion of the progeny of the cross G₁G₂M₁M₂T₂T₂xG₁G₂M₁M₂T₁T₂ do you expect to display colored kernels?

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Textbook Question

New Zealand lamb breeders measure the following variance values for their herd.

Calculate the broad sense heritability (H²) and the narrow sense heritability (h²) for each trait in this lamb herd.

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Textbook Question

New Zealand lamb breeders measure the following variance values for their herd.

How would you characterize the potential response to selection (R) for each trait?

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Textbook Question

Cattle breeders would like to improve the protein content and butterfat content of milk produced by a herd of cows. Narrow sense heritability values are 0.60 for protein content and 0.80 for butterfat content. The average percentages of these traits in the herd and the percentages of the traits in cows selected for breeding are as follows. Trait Herd Average Selected Cows Protein content 20.2% 22.7% Butterfat content  6.5%  7.4% Which trait is likely to be the most responsive to artificial selection applied by the cattle breeders through selection of cows for mating?

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Textbook Question

In human gestational development, abnormalities of the closure of the lower part of the mid-face can result in cleft lip, if the lip alone is affected by the closure defect, or in cleft lip and palate (the roof of the mouth), if the closure defect is more extensive. Cleft lip and cleft lip with cleft palate are multifactorial disorders that are threshold traits. A family with a history of either condition has a significantly increased chance of a recurrence of mid-face cleft disorder in comparison with families without such a history. However, the recurrence risk of a mid-face cleft disorder is higher in families with a history of cleft lip with cleft palate than in families with a history of cleft lip alone. Suppose a friend of yours who has not taken genetics asks you to explain these observations. Construct a genetic explanation for the increased recurrence risk of mid-face clefting in families that have a history of cleft disorders versus families without a history of such disorders.

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Textbook Question

In human gestational development, abnormalities of the closure of the lower part of the mid-face can result in cleft lip, if the lip alone is affected by the closure defect, or in cleft lip and palate (the roof of the mouth), if the closure defect is more extensive. Cleft lip and cleft lip with cleft palate are multifactorial disorders that are threshold traits. A family with a history of either condition has a significantly increased chance of a recurrence of mid-face cleft disorder in comparison with families without such a history. However, the recurrence risk of a mid-face cleft disorder is higher in families with a history of cleft lip with cleft palate than in families with a history of cleft lip alone. Construct a similar explanation of why the recurrence risk of a cleft disorder is higher in families with a history of cleft lip with cleft palate than in families with a history of cleft lip alone.

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