Textbook Question
Provide a definition and an example for each of the following terms:
multifactorial inheritance
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Ch. 4 - Gene Interaction
Chapter 4, Problem 7
Provide a definition and an example for each of the following terms:
threshold trait
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Understand that a threshold trait is a type of quantitative trait that is determined by multiple genetic and environmental factors, but is expressed in a binary manner (e.g., present or absent).
Recognize that threshold traits are often related to diseases or conditions where an individual either has the condition or does not, based on whether their genetic liability exceeds a certain threshold.
Consider the concept of liability, which is an underlying continuous variable that represents the combined effect of genetic and environmental factors on the trait.
Visualize the distribution of liability in a population, where only individuals whose liability exceeds a certain threshold will express the trait.
For example, think of a condition like type 2 diabetes, where individuals with a liability above a certain threshold develop the disease, while those below the threshold do not.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Threshold Trait
A threshold trait is a type of genetic trait that is not continuously variable but instead exhibits a distinct cutoff point. Individuals may possess a certain genetic predisposition, but the trait only manifests when a specific threshold of genetic or environmental factors is surpassed. For example, a person may have a genetic risk for a condition like diabetes, but they will only develop the disease if they exceed a certain weight or lifestyle threshold.
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Traits and Variance
Polygenic Inheritance
Threshold traits are often influenced by polygenic inheritance, where multiple genes contribute to the phenotype. Each gene may have a small effect, and the cumulative impact of these genes determines whether the threshold is crossed. This complexity means that predicting the occurrence of threshold traits can be challenging, as it involves understanding the interactions of various genetic factors.
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Environmental Factors
Environmental factors play a crucial role in the expression of threshold traits. These factors can include lifestyle choices, diet, exposure to toxins, and other external influences that interact with genetic predispositions. For instance, an individual may have a genetic predisposition for a threshold trait like hypertension, but it may only develop if they experience certain environmental stressors, such as high salt intake or lack of exercise.
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Related Practice
Textbook Question
Provide a definition and an example for each of the following terms:
polygenic inheritance
286
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Textbook Question
Provide a definition and an example for each of the following terms:
quantitative trait locus
200
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Textbook Question
Two genes interact to produce various phenotypic ratios among F₂ progeny of a dihybrid cross. Design a different pathway explaining each of the F₂ ratios below, using hypothetical genes R and T and assuming that the dominant allele at each locus catalyzes a different reaction or performs an action leading to pigment production. The recessive allele at each locus is null (loss-of-function). Begin each pathway with a colorless precursor that produces a white or albino phenotype if it is unmodified. The ratios are for F₂ progeny produced by crossing wild-type F₁ organisms with the genotype RrTt.
9/16 dark blue : 6/16 light blue : 1/16 white
203
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Textbook Question
Two genes interact to produce various phenotypic ratios among F₂ progeny of a dihybrid cross. Design a different pathway explaining each of the F₂ ratios below, using hypothetical genes R and T and assuming that the dominant allele at each locus catalyzes a different reaction or performs an action leading to pigment production. The recessive allele at each locus is null (loss-of-function). Begin each pathway with a colorless precursor that produces a white or albino phenotype if it is unmodified. The ratios are for F₂ progeny produced by crossing wild-type F₁ organisms with the genotype RrTt.
12/16 white : 3/16 green : 1/16 yellow
221
views
Textbook Question
Two genes interact to produce various phenotypic ratios among F₂ progeny of a dihybrid cross. Design a different pathway explaining each of the F₂ ratios below, using hypothetical genes R and T and assuming that the dominant allele at each locus catalyzes a different reaction or performs an action leading to pigment production. The recessive allele at each locus is null (loss-of-function). Begin each pathway with a colorless precursor that produces a white or albino phenotype if it is unmodified. The ratios are for F₂ progeny produced by crossing wild-type F₁ organisms with the genotype RrTt.
9/16 green : 3/16 yellow : 3/16 blue : 1/16 white
233
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