Genetics Chapter 8: Complex Inheritance
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Questions and Answers

What is the primary reason why diseases such as myocardial infarction and cancer do not follow a Mendelian pattern of inheritance?

  • They are inherited in an autosomal recessive pattern.
  • They are caused by a single gene mutation.
  • They result from complex interactions between multiple genetic and environmental factors. (correct)
  • They are caused by environmental factors only.

    • What is a key characteristic of multifactorial inheritance patterns?

  • They result from the interaction of multiple genetic and environmental factors. (correct)
  • They are only influenced by environmental factors.
  • They always follow a Mendelian pattern.
  • They are caused by a single gene mutation.

    • Why are relatives of an affected individual more likely to experience the same disease?

  • Because they have a different genetic makeup.
  • Because they are more likely to experience the same gene-gene and gene-environment interactions. (correct)
  • Because they inherit a single gene mutation.
  • Because they are exposed to the same environmental factors.

    • What type of inheritance pattern is characterized by the collective effect of the genotype at multiple loci?

    <p>Polygenic</p> Signup and view all the answers

    What can environmental exposures do to the disease process?

    <p>Trigger, accelerate, exacerbate, or protect against the disease process.</p> Signup and view all the answers

    Why do diseases such as congenital birth defects and Alzheimer disease 'run in families'?

    <p>Because they result from complex interactions between genetic and environmental factors.</p> Signup and view all the answers

    What is the result of the interaction between the collective effect of the genotype and environmental exposures?

    <p>A multifactorial inheritance pattern.</p> Signup and view all the answers

    What is a measurable physiological or biochemical quantity related to a disease, such as height or blood pressure?

    <p>Quantitative trait</p> Signup and view all the answers

    Why may familial aggregation of a disease not necessarily imply a genetic contribution?

    <p>Because families share environmental factors and cultural attitudes</p> Signup and view all the answers

    What is the term for when two related individuals in a family have the same disease?

    <p>Concordance</p> Signup and view all the answers

    Why may two relatives with the same disease not necessarily have the same predisposing genotypes?

    <p>Because one relative has a genocopy or phenocopy of the disease</p> Signup and view all the answers

    What is a term for a disease that is either present or absent?

    <p>Qualitative trait</p> Signup and view all the answers

    What may explain why one relative is unaffected by a disease despite sharing a genotype at loci that predispose to disease?

    <p>They have not experienced the necessary environmental factors</p> Signup and view all the answers

    What is a phenocopy of a disease?

    <p>A disease that has the same phenotype as another disease but is caused by different genetic or environmental factors</p> Signup and view all the answers

    What pattern is observed in the prevalence of disease among relatives of a proband?

    <p>The disease is more common among close relatives and becomes less common in relatives who are less closely related.</p> Signup and view all the answers

    What is the expected pattern of concordance for disease among twins?

    <p>Monozygotic twins show higher concordance for disease than dizygotic twins.</p> Signup and view all the answers

    Which of the following is an example of a multifactorial trait influenced by both genetic and environmental factors?

    <p>Type 1 Diabetes Mellitus</p> Signup and view all the answers

    What is the approximate incidence of congenital heart defects (CHDs) per 1000 births?

    <p>4-8 per 1000 births</p> Signup and view all the answers

    Which of the following types of congenital heart defects (CHDs) accounts for 50% of all CHDs?

    <p>Flow lesions</p> Signup and view all the answers

    What is the worldwide prevalence of schizophrenia?

    <p>1% of the population</p> Signup and view all the answers

    For which type of congenital heart defects (CHDs) can relatives of index patients be offered reassurance that their risk is no greater than that of the general population?

    <p>All types of CHDs except flow lesions</p> Signup and view all the answers

    What does the variance of a measured quantity in the population represent?

    <p>The degree of spread of values to either side of the mean</p> Signup and view all the answers

    What is the shape of the graph resulting from plotting the number of individuals with a particular quantitative value against the value?

    <p>Bell-shaped</p> Signup and view all the answers

    What is the term for the range of values within which most individuals in a population fall?

    <p>Normal range</p> Signup and view all the answers

    What is a key characteristic of diseases with complex inheritance?

    <p>They demonstrate familial aggregation</p> Signup and view all the answers

    What is an example of lack of penetrance despite identical genotypes?

    <p>monozygotic twins with different phenotypes</p> Signup and view all the answers

    Why may pairs of relatives who share disease-predisposing genotypes at relevant loci still be discordant for phenotype?

    <p>Because of the influence of environmental factors</p> Signup and view all the answers

    What is a key difference between diseases with complex inheritance and single-gene disorders?

    <p>The pattern of inheritance</p> Signup and view all the answers

    What is the term for the study of the genetic factors that contribute to the development of a disease?

    <p>Genetic epidemiology</p> Signup and view all the answers

    What is the purpose of comparing measurements in children with the 'normal' expected measurements for their sex and age?

    <p>To assess health and disease</p> Signup and view all the answers

    Study Notes

    Genetics of Common Disorders with Complex Inheritance

    • Diseases such as congenital birth defects, myocardial infarction, cancer, mental illness, diabetes, and Alzheimer disease cause morbidity and premature mortality in nearly two of every three individuals during their lifetimes.
    • These diseases "run in families" but do not follow a simple Mendelian pattern of inheritance.
    • Instead, they result from complex interactions between multiple genetic and environmental factors, making them multifactorial or complex inheritance patterns.

    Qualitative and Quantitative Traits

    • Complex phenotypes of multifactorial disorders can be divided into two major categories: qualitative and quantitative traits.
    • Qualitative traits are discrete, meaning an individual either has the disease or not.
    • Quantitative traits are measurable physiological or biochemical quantities, such as height, blood pressure, or serum cholesterol concentration, that underlie many common diseases.

    Genetic Analysis of Qualitative Disease Traits

    • Familial aggregation of disease occurs when affected individuals cluster in families, but this does not necessarily mean the disease has a genetic contribution.
    • Concordance and discordance:
      • Concordance: when two related individuals have the same disease.
      • Discordance: when one member of the pair is affected, and the other is not.
    • Discordance can occur even when relatives share a genotype, if the unaffected individual has not experienced the necessary environmental factors to trigger the disease.

    Examples of Multifactorial Traits

    • Multifactorial congenital malformations
    • Mental illness
    • Coronary artery disease
    • Digenic retinitis pigmentosa
    • Venous thrombosis
    • Hirschsprung disease
    • Type 1 diabetes mellitus
    • Alzheimer disease

    Multifactorial Congenital Malformations

    • Congenital heart defects (CHDs) occur in 4 to 8 per 1000 births.
    • Five main groups of CHDs can be distinguished:
      • Flow lesions
      • Defects in cell migration
      • Defects in cell death
      • Abnormalities in extracellular matrix
      • Defects in targeted growth

    Neuropsychiatric Disorders

    • Schizophrenia affects 1% of the world's population.
    • Neuropsychiatric disorders occur in 4% of the human population worldwide.

    The Normal Distribution

    • The normal distribution is a bell-shaped curve representing the distribution of quantitative values in a population.
    • The variance (or standard deviation, σ) measures the degree of spread of values around the mean.
    • The normal range is used to assess health and disease in individuals, where values outside the normal range are considered abnormal.

    Characteristics of Inheritance of Complex Diseases

    • Genes contribute to diseases with complex inheritance, but these diseases are not single-gene disorders.
    • Diseases with complex inheritance often demonstrate familial aggregation due to shared disease-predisposing alleles.
    • Pairs of relatives who share disease-predisposing genotypes may still be discordant for phenotype due to the role of nongenetic factors in disease causation.

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    Related Documents

    Genetics of Common Disorders with Complex Inheritance PDF 2024

    Description

    This quiz covers qualitative and quantitative traits, twin studies, and genetic and environmental modifiers of single-gene disorders. It also includes examples of multifactorial traits and the normal distribution.

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