Questions and Answers
What is the term for the random inactivation of X-chromosomes in females?
What was discovered in 1959 to be located on the Y-chromosome?
What is the name of the condensed piece of chromatin at the edge of nuclei in XX individuals?
What is the result of Lyonization in females?
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When does the inactivation of X-chromosomes occur in females?
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What is the purpose of Lyonization in females?
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Who demonstrated that only one of the X-chromosomes in females is active?
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What is the number of Barr bodies in a cell in relation to the number of X-chromosomes?
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What is the primary goal of non-directive counseling?
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What type of counseling involves evaluating risks for future offspring and family members?
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What is the primary purpose of genetic screening?
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What type of testing confirms a diagnosis and may guide treatment?
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What is the purpose of carrier screening?
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What type of testing involves evaluating asymptomatic individuals for later onset disorders?
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What is retrospective counseling focused on?
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What is the difference between genetic screening and diagnostic testing?
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Which of the following individuals would benefit from referral to a genetic counselor?
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What is the purpose of taking a complete family history in genetic counseling?
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What is a significant advantage of chromosomal microarray over standard chromosome study?
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What type of genetic alteration may be detected during genetic testing, but whose clinical implications are uncertain?
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Which of the following is NOT a requirement for a standard chromosome study?
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What is the primary goal of genetic counseling?
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Which of the following is a limitation of chromosomal microarray?
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Why is it important to communicate with a family's physicians in genetic counseling?
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What emotional response is a person likely to experience when receiving genetic information about a potential risk for a genetic condition?
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What is the primary role of genetic counselors in providing emotional support?
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What is a key factor to consider when making decisions about genetic testing?
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What is the primary goal of genetic counseling in relation to decision-making?
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What is a psychosocial aspect of genetic counseling?
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Why is genetic counseling important for individuals with genetic conditions?
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What is a consideration for individuals when making decisions about genetic testing?
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What is the role of genetic counselors in relation to ethics and privacy?
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What is the effect of the TaM allele on the striping pattern of a tabby cat?
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What is the characteristic of single gene disorders or traits?
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What is the recurrence risk to children of an affected person for an autosomal dominant trait?
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What type of inheritance pattern is characteristic of cystic fibrosis?
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What is the effect of a new mutation in an autosomal dominant trait?
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What is the characteristic of achondroplasia?
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What type of disorders are often caused by variations at a single genetic locus?
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What is the characteristic of Marfan syndrome?
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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.
