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Ch. 25 - Quantitative Genetics and Multifactorial Traits
Chapter 24, Problem 18

In a population of tomato plants, mean fruit weight is 60 g and h² is 0.3. Predict the mean weight of the progeny if tomato plants whose fruit averaged 80 g were selected from the original population and interbred.

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Identify the given values: mean fruit weight of the original population (\( \bar{X} = 60 \) g), heritability (\( h^2 = 0.3 \)), and mean fruit weight of selected plants (\( \bar{X}_s = 80 \) g).
Calculate the selection differential (\( S \)), which is the difference between the mean of the selected parents and the mean of the original population: \( S = \bar{X}_s - \bar{X} \).
Use the breeder's equation to predict the response to selection (\( R \)): \( R = h^2 \times S \).
Determine the mean weight of the progeny (\( \bar{X}' \)) by adding the response to selection (\( R \)) to the mean of the original population: \( \bar{X}' = \bar{X} + R \).
Summarize the steps to predict the mean weight of the progeny based on the calculated values.

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Key Concepts

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

Heritability (h²)

Heritability (h²) is a measure of how much of the variation in a trait, such as fruit weight, can be attributed to genetic differences among individuals in a population. A heritability value of 0.3 indicates that 30% of the variation in fruit weight is due to genetic factors, while the remaining 70% is influenced by environmental factors. This concept is crucial for predicting how traits will be passed on to the next generation.
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Selection Differential

The selection differential is the difference between the mean trait value of the selected individuals and the mean trait value of the entire population. In this case, the selected tomato plants have an average fruit weight of 80 g, while the population mean is 60 g, resulting in a selection differential of 20 g. This value helps in estimating the expected change in the trait in the progeny due to selection.
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Response to Selection

Response to selection refers to the expected change in the mean trait value of the next generation as a result of selective breeding. It can be calculated using the formula: Response = h² × Selection Differential. In this scenario, with a heritability of 0.3 and a selection differential of 20 g, the response to selection can be predicted, allowing us to estimate the mean weight of the progeny.
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Related Practice
Textbook Question

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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Textbook Question

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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Textbook Question

Suppose you want to develop a population of Drosophila that would rapidly learn to avoid certain substances the flies could detect by smell. Based on the heritability estimate you obtained in Problem 16, do you think it would be worth doing this by artificial selection? Why or why not?

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Textbook Question

In a population of 100 inbred, genotypically identical rice plants, variance for grain yield is 4.67. What is the heritability for yield? Would you advise a rice breeder to improve yield in this strain of rice plants by selection?

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Textbook Question

Many traits of economic or medical significance are determined by quantitative trait loci (QTLs) in which many genes, usually scattered throughout the genome, contribute to expression.

What general procedures are used to identify such loci?

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Textbook Question

Many traits of economic or medical significance are determined by quantitative trait loci (QTLs) in which many genes, usually scattered throughout the genome, contribute to expression.

What is meant by the term cosegregate in the context of QTL mapping? Why are markers such as RFLPs, SNPs, and microsatellites often used in QTL mapping?

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