3. Extensions to Mendelian Inheritance

Pleiotropy

3. Extensions to Mendelian Inheritance

Pleiotropy: Videos & Practice Problems

Topic summary

Pleiotropy occurs when a single gene influences multiple phenotypic traits. This can happen through various mechanisms: the gene may have multiple functions, be expressed in different cell types, or be active at different developmental stages. A notable example is cystic fibrosis, caused by a mutation in the CFTR gene, which disrupts chloride regulation, leading to diverse symptoms like thick mucus in the lungs and other systemic issues. Understanding pleiotropy is crucial for grasping complex traits and genetic disorders.

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Pleiotropy

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Pleiotropy Video Summary

Pleiotropy refers to the phenomenon where a single gene influences multiple phenotypic traits in an organism. This can occur when a mutation in a gene leads to various effects across different systems or characteristics. For instance, a single mutated gene may be responsible for conditions such as breast cancer, neurological defects, or physical traits like short fingers and breathing difficulties. The underlying mechanisms through which pleiotropy manifests can be categorized into three main pathways.

Firstly, a gene may have multiple functions due to its involvement in different biological pathways. For example, if a gene plays a role in two distinct pathways, it can lead to varied outcomes depending on which pathway is activated. Secondly, the expression of a gene in different cell types can result in diverse effects. If a gene is expressed in both the kidney and the brain, it can produce specific phenotypic effects in those organs without affecting others. Lastly, a gene may be expressed at different developmental stages, meaning that its effects can vary significantly over an organism's lifespan. A mutation might have a noticeable impact during infancy but could diminish or re-emerge later in life, such as at age 50, reflecting the developmental context in which the gene is active.

A classic example of pleiotropy is cystic fibrosis, which is caused by a mutation in the CFTR gene. The CFTR gene encodes a transmembrane protein that is crucial for regulating chloride ion concentrations in cells. Proper chloride regulation is essential for various physiological functions, particularly in the lungs and sweat glands. When the CFTR gene is mutated, it disrupts chloride balance, leading to a range of symptoms. For instance, individuals with cystic fibrosis often experience thick mucus buildup in the lungs due to impaired fluid regulation, resulting in respiratory issues. Additionally, they may have salty sweat, which is a direct consequence of the disrupted chloride transport. This single genetic mutation exemplifies how one gene can lead to multiple phenotypic manifestations, illustrating the concept of pleiotropy effectively.

Problem

Which of the following is NOT an example of a pleiotropic trait?

A single gene is expressed and has different functions in the brain, arm, and kidneys

A single gene can increase blood pressure, fire neurons, and keeps mucus in the lungs

Two genes are responsible for filtering urine in the kidneys

A single gene is expressed consistently throughout the life of an organism, but as the organism changes it has different effects

Problem

A pleotropic trait is controlled by…

1 gene

2 genes

3 genes

4+ genes

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Here’s what students ask on this topic:

What is pleiotropy and how does it affect phenotypes?

Pleiotropy occurs when a single gene influences multiple phenotypic traits. This can happen through various mechanisms: the gene may have multiple functions, be expressed in different cell types, or be active at different developmental stages. For example, a gene might be involved in two different biochemical pathways, leading to distinct phenotypic outcomes. Alternatively, the gene could be expressed in different tissues, such as the brain and kidney, causing effects in both organs. Lastly, the gene might be active at different times in an organism's life, leading to age-specific traits. Understanding pleiotropy is crucial for grasping complex traits and genetic disorders.

How does the CFTR gene mutation lead to cystic fibrosis?

The CFTR gene mutation causes cystic fibrosis by disrupting the regulation of chloride ions across cell membranes. CFTR is a transmembrane protein responsible for chloride transport. When mutated, it fails to regulate chloride levels properly, leading to thick mucus in the lungs, digestive issues, and other systemic problems. This single gene mutation results in multiple phenotypic effects, exemplifying pleiotropy. The thick mucus in the lungs, for instance, is due to improper fluid regulation, while other symptoms arise from similar disruptions in chloride balance in different tissues.

What are the main mechanisms through which pleiotropy occurs?

Pleiotropy can occur through three main mechanisms: 1) A gene may have multiple functions, participating in different biochemical pathways that lead to various phenotypic outcomes. 2) The gene might be expressed in different cell types, causing effects in multiple tissues or organs. For example, a gene expressed in both the brain and kidney will affect both organs. 3) The gene could be active at different developmental stages, leading to age-specific traits. For instance, a gene might cause one effect in early childhood and another in middle age.

Can you provide an example of a pleiotropic gene and its effects?

A classic example of a pleiotropic gene is the CFTR gene, which, when mutated, causes cystic fibrosis. This single gene mutation leads to multiple phenotypic effects, such as thick mucus in the lungs, digestive issues, and other systemic problems. The CFTR protein is responsible for regulating chloride ion transport across cell membranes. When this regulation is disrupted, it affects various tissues differently, leading to the diverse symptoms seen in cystic fibrosis patients. This illustrates how one gene can have multiple, widespread effects on an organism's phenotype.

Why is understanding pleiotropy important in genetics?

Understanding pleiotropy is crucial in genetics because it helps explain how single gene mutations can lead to complex traits and multiple symptoms. This knowledge is essential for diagnosing and treating genetic disorders. For instance, recognizing that a single gene can affect multiple organs or developmental stages can guide more comprehensive medical evaluations and interventions. Additionally, understanding pleiotropy can aid in the development of targeted therapies that address the various phenotypic effects of a single gene mutation, improving patient outcomes.

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