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Concept explainers
Which of the following traits would you expect to be inherited as quantitative traits?
a. body weight in chickens
b. growth rate in sheep
c. milk production in cattle
d. fruit weight in tomatoes
e. coat color in dogs
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To analyze:
Determine the expected quantitative traits from the following:
Body weight in chicken
Growth rate in sheep
Milk production in cattle
Fruits weight in tomatoes
Coat color in dogs
Introduction:
Multifactorial traits are the results of genetic and non-genetic variation that can contribute to the variation in phenotypes of certain traits. These multifactorial traits can be classified as quantitative traits or qualitative traits. Qualitative phenotypic variations are discontinuous variation whereas quantitative phenotypic variations are continuous variation. The effect of multiple genes which exerts same or different amount of influence on the phenotypes leads to the continuous variation in the phenotypes of polygenic traits. The influence of multiple genes leads to a number of traits called polygenic traits. The incremental contributions by multiple genes result in continuous phenotypic variation. These multiple genes are called additive genes and their effects are called additive gene effects.
Explanation of Solution
The additive effects of multiple genes contribute to the body weight of the chicken. But chickens have different body mass which suggests that each gene contributes a certain quantity of body weight. This difference in body mass is responsible for continuous variation. Therefore, it is a quantitative trait.
Continuous variation is also seen in the growth rate of sheep. The additive effect of multiple genes is responsible for different growth rates. So, the growth rate in sheep is a quantitative trait.
The amount of milk produced by each cattle is varying continuously. This suggests that the phenotypic trait is controlled by a number of genes. Each gene may add a certain quantity of milk. Therefore, milk production in cattle is a quantitative trait.
Tomatoes are also have different weights. This difference in the weight of tomatoes is contributed by different genes. This suggests that continuous variation in weight difference is an additive gene effect. Therefore, fruit weight in tomatoes is a quantitative trait.
It is observed that the coat color of the dogs is not continuously varied. Contrast is present in the coat color of dogs. Therefore, coat color in dogs is not a quantitative trait.
The quantitative traits are classified based on continuous and discontinuous phenotypic variation.
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Genetic Analysis: An Integrated Approach (3rd Edition)
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