Genetics of Tabby Cats
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Questions and Answers

What is the term for the random inactivation of X-chromosomes in females?

  • XY Inactivation
  • Sex Determination
  • Lyonization (correct)
  • Barr Body

    • What was discovered in 1959 to be located on the Y-chromosome?

  • The male sex-determining gene (SRY) (correct)
  • A gene that determines female sex
  • A gene that inactivates X-chromosomes
  • A gene that activates X-chromosomes

    • What is the name of the condensed piece of chromatin at the edge of nuclei in XX individuals?

  • Sex Chromosome
  • Barr Body (correct)
  • XY Chromatin
  • Lyon Body

    • What is the result of Lyonization in females?

    <p>One X-chromosome is active and the other is permanently inactivated</p> Signup and view all the answers

    When does the inactivation of X-chromosomes occur in females?

    <p>Early in embryologic development</p> Signup and view all the answers

    What is the purpose of Lyonization in females?

    <p>To compensate for the difference in gene dosage between XX and XY individuals</p> Signup and view all the answers

    Who demonstrated that only one of the X-chromosomes in females is active?

    <p>Mary Lyon</p> Signup and view all the answers

    What is the number of Barr bodies in a cell in relation to the number of X-chromosomes?

    <p>One less than the number of X-chromosomes</p> Signup and view all the answers

    What is the primary goal of non-directive counseling?

    <p>To provide as much information as possible to the patient</p> Signup and view all the answers

    What type of counseling involves evaluating risks for future offspring and family members?

    <p>Prospective counseling</p> Signup and view all the answers

    What is the primary purpose of genetic screening?

    <p>To test an entire population for pathologic genetic variants</p> Signup and view all the answers

    What type of testing confirms a diagnosis and may guide treatment?

    <p>Diagnostic testing</p> Signup and view all the answers

    What is the purpose of carrier screening?

    <p>To provide prenatal risk counseling</p> Signup and view all the answers

    What type of testing involves evaluating asymptomatic individuals for later onset disorders?

    <p>Predictive testing</p> Signup and view all the answers

    What is retrospective counseling focused on?

    <p>Evaluating people who may have a genetic condition</p> Signup and view all the answers

    What is the difference between genetic screening and diagnostic testing?

    <p>Genetic screening is used for asymptomatic individuals, while diagnostic testing is used for symptomatic individuals</p> Signup and view all the answers

    Which of the following individuals would benefit from referral to a genetic counselor?

    <p>A couple who have had multiple miscarriages</p> Signup and view all the answers

    What is the purpose of taking a complete family history in genetic counseling?

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

    What is a significant advantage of chromosomal microarray over standard chromosome study?

    <p>It does not need living cells</p> Signup and view all the answers

    What type of genetic alteration may be detected during genetic testing, but whose clinical implications are uncertain?

    <p>Variant of unknown significance (VUS)</p> Signup and view all the answers

    Which of the following is NOT a requirement for a standard chromosome study?

    <p>DNA segments attached to a silicon chip</p> Signup and view all the answers

    What is the primary goal of genetic counseling?

    <p>To counsel patients on genetic screening and diagnostic testing options</p> Signup and view all the answers

    Which of the following is a limitation of chromosomal microarray?

    <p>It does not pick up balanced translocations</p> Signup and view all the answers

    Why is it important to communicate with a family's physicians in genetic counseling?

    <p>To coordinate medical care</p> Signup and view all the answers

    What emotional response is a person likely to experience when receiving genetic information about a potential risk for a genetic condition?

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

    What is the primary role of genetic counselors in providing emotional support?

    <p>To be attuned to emotional reactions and provide appropriate support</p> Signup and view all the answers

    What is a key factor to consider when making decisions about genetic testing?

    <p>Potential impact on family members</p> Signup and view all the answers

    What is the primary goal of genetic counseling in relation to decision-making?

    <p>To assist individuals in making informed decisions</p> Signup and view all the answers

    What is a psychosocial aspect of genetic counseling?

    <p>Emotional support</p> Signup and view all the answers

    Why is genetic counseling important for individuals with genetic conditions?

    <p>To provide emotional support and guidance</p> Signup and view all the answers

    What is a consideration for individuals when making decisions about genetic testing?

    <p>Reproductive choices</p> Signup and view all the answers

    What is the role of genetic counselors in relation to ethics and privacy?

    <p>To ensure confidentiality and respect for individuals' autonomy</p> Signup and view all the answers

    What is the effect of the TaM allele on the striping pattern of a tabby cat?

    <p>It produces a mackerel pattern</p> Signup and view all the answers

    What is the characteristic of single gene disorders or traits?

    <p>They are caused by variations at one genetic locus</p> Signup and view all the answers

    What is the recurrence risk to children of an affected person for an autosomal dominant trait?

    <p>50%</p> Signup and view all the answers

    What type of inheritance pattern is characteristic of cystic fibrosis?

    <p>Autosomal recessive</p> Signup and view all the answers

    What is the effect of a new mutation in an autosomal dominant trait?

    <p>The parent is never affected</p> Signup and view all the answers

    What is the characteristic of achondroplasia?

    <p>It is an autosomal dominant disorder</p> Signup and view all the answers

    What type of disorders are often caused by variations at a single genetic locus?

    <p>Inborn errors of metabolism</p> Signup and view all the answers

    What is the characteristic of Marfan syndrome?

    <p>It is an autosomal dominant disorder</p> Signup and view all the answers

    Study Notes

    Tabby Cats and Genetic Locus

    • The striping pattern in tabby cats is controlled by the Tabby locus, with two alleles: TaM (mackerel pattern) and Tab (classic or blotched pattern).
    • The Mackerel allele (TaM) is dominant, while the Classic allele (Tab) is recessive.

    Single Gene Disorders or Traits

    • Single gene disorders or traits follow simple inheritance patterns (Mendelian) and are due to variations at one genetic locus.
    • Such disorders can be dominant, recessive, or X-linked.
    • There are over 5,000 described single gene disorders, including:
      • Most inborn errors of metabolism (e.g., PKU, urea cycle, organic acid disorders)
      • Cystic fibrosis
      • Chondrodysplasias (e.g., Achondroplasia, Stickler syndrome, SED)
      • Craniosynostosis (e.g., Apert, Pfeiffer, Crouzon)
      • Some syndromes (e.g., Marfan, Neurofibromatosis, Tuberous sclerosis, Fragile-X)

    Dominant Inheritance

    • Only one gene variant is needed to cause problems.
    • Heterozygotes manifest the trait.
    • The condition can be passed from parent to child.
    • There is a 50% recurrence risk to children of an affected person.
    • The condition can be caused by a new mutation (even if the parent is unaffected).

    Lyonization and Barr Body

    • Lyonization refers to the random inactivation of X-chromosomes in females.
    • The Barr body is a condensed piece of chromatin at the edge of nuclei in XX individuals (female cats), but not in XY individuals (male cats).
    • The number of Barr bodies in a cell is one less than the number of X-chromosomes in the cell nucleus.

    Genetic Counseling

    • Non-directive counseling provides information and leaves decision-making to the patient/family.
    • Types of counseling include:
      • Prospective counseling: evaluating risks for future offspring or family members.
      • Retrospective counseling: diagnosis, prognosis, and treatment options for affected individuals.
    • Genetic screening tests an entire population for pathologic genetic variants.
    • Differentiate between genetic screening, diagnostic testing, and predictive testing.

    Genetic Testing

    • Chromosome study (karyotype) requires living cells with nuclei and involves culturing cells to make them divide, staining, and analyzing with a microscope.
    • Chromosomal microarray (CGH) uses DNA segments attached to a silicon chip and does not require living cells or staining.
    • CGH provides better resolution than standard chromosome studies and can detect smaller changes.

    Psychosocial Aspects of Genetic Counseling

    • Emotional impact: receiving genetic information can evoke anxiety, fear, guilt, sadness, and uncertainty.
    • Genetic counselors need to provide appropriate support and guidance to individuals and families.
    • Decision-making: genetic testing involves complex decisions, and genetic counselors assist individuals in understanding their options and making informed decisions.
    • Ethical issues, privacy, financing, and follow-up are also important aspects of genetic counseling.

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    Description

    This quiz covers the genetics of Tabby cats, including the striping pattern controlled by the Tabby locus and the Law of Dominance. It explains how the mackerel and classic patterns are produced.

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