Lecture 17
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Questions and Answers

What type of genetic disorder is caused by mutations in a single gene?

  • Mitochondrial disorder
  • Cytogenetic disorder
  • Multifactorial disorder
  • Single-gene disorder (correct)

    • What determines the pattern of inheritance in single-gene disorders?

  • The number of siblings
  • The age of the parent
  • The severity of the disease
  • The chromosomal location of the gene locus (correct)

    • What is the term for the position of a gene on a chromosome?

  • Phenotype
  • Locus (correct)
  • Allele
  • Genotype

    • What is the characteristic of a dominant single-gene disorder?

    <p>It is expressed when only one gene copy has a pathogenic variant</p> Signup and view all the answers

    What is the term for genetic disorders caused by defects in chromosomes or part of a chromosome?

    <p>Cytogenetic disorders</p> Signup and view all the answers

    What is the significance of identifying the inheritance pattern in single-gene disorders?

    <p>It helps in calculating the chances of having a child with the disease</p> Signup and view all the answers

    What type of genetic disorder is caused by defects in two or more genes along with environmental factors?

    <p>Multifactorial disorder</p> Signup and view all the answers

    What is the characteristic of a recessive single-gene disorder?

    <p>It is expressed only when both gene copies have the pathogenic variant</p> Signup and view all the answers

    What is the term for the position of a gene on a chromosome?

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

    What is the term for different alleles at a locus?

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

    What is the term for identical alleles at a locus?

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

    What is the first step in establishing a pattern of inheritance of a particular disease within a family?

    <p>Obtaining information about the family history</p> Signup and view all the answers

    What is the term for the person through whom the family came to medical attention?

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

    What is the graphical representation of the family tree?

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

    What is the term for the relatives of the index?

    <p>First-degree relatives</p> Signup and view all the answers

    Which of the following is a classification of relatives?

    <p>Parent, sibling, and offspring</p> Signup and view all the answers

    What is the characteristic of vertical transmission?

    <p>The disease passed from generation to generation.</p> Signup and view all the answers

    What type of inheritance pattern is characterized by a phenotype that is expressed when only one gene copy has a pathogenic variant?

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

    In Autosomal Dominant inheritance, what is the genotype of an affected individual?

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

    What is the characteristic of X-linked recessive inheritance?

    <p>The condition passes from unaffected female.</p> Signup and view all the answers

    What is the significance of mitochondrial DNA in patterns of inheritance?

    <p>It is involved in a separate pattern of inheritance.</p> Signup and view all the answers

    What is the difference between autosomal and sex-linked inheritance?

    <p>Autosomal inheritance is on chromosomes 1 to 22, while sex-linked is on X and Y chromosomes.</p> Signup and view all the answers

    What is the characteristic of horizontal transmission?

    <p>The disease appears in one generation with phenotypically healthy parents.</p> Signup and view all the answers

    What is the significance of the chromosomal location of the gene locus in patterns of inheritance?

    <p>It determines the type of inheritance pattern.</p> Signup and view all the answers

    Which autosomal dominant disease is caused by a mutation in the FBN1 gene encoding fibrillin?

    <p>Marfan Syndrome</p> Signup and view all the answers

    In Autosomal Dominant inheritance, what is the minimum number of affected parents required?

    <p>At least one</p> Signup and view all the answers

    What is the characteristic of Autosomal Dominant inheritance in terms of gender?

    <p>Males and females are equally affected</p> Signup and view all the answers

    What is the characteristic of Autosomal Recessive inheritance in terms of the genotype of the affected individual?

    <p>Homozygous for the mutant allele</p> Signup and view all the answers

    What determines the pattern of inheritance in Autosomal Recessive disorders?

    <p>Chromosomal location of the gene locus and whether the phenotype is recessive</p> Signup and view all the answers

    What is the probability of a child being healthy if one parent is affected and the other is unaffected?

    <p>½ (50%)</p> Signup and view all the answers

    What is the characteristic of a recessive allele in Autosomal Recessive inheritance?

    <p>Expressed only when the two gene copies have the pathogenic variant</p> Signup and view all the answers

    What is the probability of a child being affected if one parent is homozygous affected and the other is unaffected?

    <p>½ (50%)</p> Signup and view all the answers

    What is the symbol for the normal allele in the provided pedigree?

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

    Which of the following is an example of Autosomal Dominant inheritance?

    <p>Marfan Syndrome</p> Signup and view all the answers

    What is the number of autosomes in humans?

    <p>22</p> Signup and view all the answers

    What is the type of transmission shown in the pedigree?

    <p>Vertical transmission</p> Signup and view all the answers

    What is the genotype of an affected individual in an autosomal dominant inheritance pattern?

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

    What is the probability of a child being affected if both parents are carriers of the mutant allele?

    <p>½ (50%)</p> Signup and view all the answers

    What does a single bar indicate in the pedigree?

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

    What is the symbol for the mutant allele in the provided pedigree?

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

    Study Notes

    Categories of Genetic Disorders

    • Genetic disorders can be categorized into three main types: single gene disorders, cytogenetic disorders, and multifactorial disorders.

    Single Gene Disorders

    • Caused by mutations in a single gene.
    • Inheritance patterns are critical to clinical counseling and risk assessment for families.
    • Patterns of inheritance depend on:
      • Chromosomal location of the gene locus (autosome, sex chromosome, or mitochondrial DNA).
      • Whether the phenotype is dominant or recessive.

    Genotypes and Phenotypes

    • Genotype: the genetic makeup of an individual (e.g., homozygous, heterozygous, hemizygous).
    • Phenotype: the physical and behavioral characteristics of an individual.
    • Homozygous: identical alleles at a locus.
    • Heterozygous: different alleles at a locus.
    • Hemizygous: male with alleles at X and Y chromosomes.

    Pedigree Analysis

    • A pedigree is a graphical representation of a family tree with standard symbols.
    • The pedigree starts with the index or proband (the first person through whom the family came to medical attention).
    • Relatives are classified as first-degree (parents, siblings, and offspring), second-degree, and third-degree.
    • Patterns of inheritance can be identified through pedigree analysis.

    Autosomal Dominant (AD) Inheritance

    • Caused by mutations in a single gene on an autosome (chromosomes 1-22).
    • Dominant phenotype is expressed when only one gene copy has a pathogenic variant (mutation).
    • Genetic risks:
      • 50% chance of passing the affected gene to each offspring.
      • Unaffected individuals can be carriers.
    • Family pedigree:
      • Vertical transmission (disease passes from generation to generation).
      • Male-to-male transmission excludes X-linked inheritance.
      • Males and females are equally affected.

    Autosomal Dominant (AD) Diseases

    • Examples: Marfan Syndrome (FBN1 gene mutation), tall stature, long fingers, bilateral subluxation of the lens, floppy mitral valve, aortic aneurysm, and aortic dissection.

    Autosomal Recessive (AR) Inheritance

    • Caused by mutations in a single gene on an autosome (chromosomes 1-22).
    • Recessive phenotype is expressed only when both gene copies have a pathogenic variant (mutation).
    • Genetic risks:
      • Only homozygous for the mutant allele is affected.
      • Carriers are heterozygous for the mutant allele.
    • Family pedigree:
      • Vertical transmission (disease passes from generation to generation).
      • Males and females are equally affected.
      • Carriers can be identified through genetic testing.

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