Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

3. Extensions to Mendelian Inheritance

Penetrance and Expressivity

Genetics

3. Extensions to Mendelian Inheritance

Penetrance and Expressivity

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2:24 minutes

Problem 34

Textbook Question

Discuss the topic of phenotypic expression and the many factors that impinge on it.

Verified step by step guidance

Phenotypic expression refers to the observable traits or characteristics of an organism, such as height, eye color, or enzyme activity, which result from the interaction of its genotype (genetic makeup) with the environment.

Begin by understanding that phenotypic expression is influenced by genetic factors, such as dominant and recessive alleles, gene interactions (e.g., epistasis), and mutations that may alter gene function or regulation.

Environmental factors also play a significant role in phenotypic expression. For example, temperature, nutrition, light, and exposure to chemicals can modify how genes are expressed. A classic example is the coat color of Himalayan rabbits, which changes based on temperature.

Epigenetic modifications, such as DNA methylation and histone modification, can regulate gene expression without altering the DNA sequence itself. These changes can be influenced by environmental factors and may even be heritable.

Finally, consider the role of pleiotropy (where one gene affects multiple traits) and polygenic inheritance (where multiple genes contribute to a single trait). These genetic complexities further illustrate how phenotypic expression is shaped by a combination of genetic and environmental factors.

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Key Concepts

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

Phenotype

The phenotype refers to the observable characteristics or traits of an organism, which result from the interaction of its genotype (genetic makeup) with the environment. Examples of phenotypic traits include physical attributes like height, color, and behavior. Understanding phenotypes is crucial for studying how genetic and environmental factors influence the expression of traits.

Genotype-Environment Interaction

Genotype-environment interaction describes how different genotypes respond to environmental variations, leading to diverse phenotypic outcomes. For instance, a plant's growth may vary based on soil quality, light exposure, and water availability, even if the genetic potential is the same. This concept highlights the complexity of phenotypic expression, emphasizing that genetics alone does not determine traits.

Epigenetics

Epigenetics involves changes in gene expression that do not alter the DNA sequence but can be influenced by environmental factors, lifestyle, and experiences. These modifications can affect how genes are turned on or off, impacting phenotypic traits. For example, stress or diet can lead to epigenetic changes that may be passed to future generations, illustrating the dynamic interplay between genetics and the environment.

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Related Practice

Textbook Question

Define and distinguish incomplete penetrance and variable expressivity.

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Textbook Question

Brachydactyly type D is a human autosomal dominant condition in which the thumbs are abnormally short and broad. In most cases, both thumbs are affected, but occasionally just one thumb is involved. The accompanying pedigree shows a family in which brachydactyly type D is segregating. Filled circles and squares represent females and males who have involvement of both thumbs. Half-filled symbols represent family members with just one thumb affected.

Is there any evidence of variable expressivity in this family? Explain.

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Textbook Question

Is there evidence of incomplete penetrance in this family? Explain.

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Textbook Question

In goats, the development of the beard is due to a recessive gene. The following cross involving true-breeding goats was made and carried to the F₂ generation:

Offer an explanation for the inheritance and expression of this trait, diagramming the cross. Propose one or more crosses to test your hypothesis.

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Textbook Question

Contrast penetrance and expressivity as the terms relate to phenotypic expression.

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Multiple Choice

Which of the following statements is true of incomplete penetrance?

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Multiple Choice

If a geneticist describes a trait as being 70% penetrant, what does this mean?