Patterns of Single-Gene Inheritance
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Questions and Answers

What is a key factor in determining the patterns shown by single-gene disorders in pedigrees?

  • The presence of a severe genetic disorder
  • The number of chromosomes affected
  • The age of onset of the disease
  • Whether the phenotype is dominant or recessive (correct)

    • What is the main difference between autosomal and X-linked disorders?

  • Autosomal disorders affect both males and females equally, while X-linked disorders affect males more severely (correct)
  • Autosomal disorders only affect females, while X-linked disorders only affect males
  • Autosomal disorders are always recessive, while X-linked disorders are always dominant
  • Autosomal disorders are inherited from the mother, while X-linked disorders are inherited from the father

    • What is the term used to describe a phenotype that is expressed in both homozygotes and heterozygotes for a mutant allele?

  • Recessive
  • Autosomal
  • X-linked
  • Dominant (correct)

    • Why do females have a double complement of X-linked genes?

    <p>Because they have two X chromosomes</p> Signup and view all the answers

    What is the term used to describe a disorder that occurs when a severe, debilitating genetic disorder has normal fitness because the onset of the disease is well past the usual reproductive age?

    <p>None of the above</p> Signup and view all the answers

    What is the purpose of X-inactivation in females?

    <p>To compensate for the double complement of X-linked genes in females</p> Signup and view all the answers

    What is a person called when they have a pair of identical alleles at a locus encoded in nuclear DNA?

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

    What is the term used to describe a genotype in which two different mutant alleles of the same gene are present?

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

    What is the term used to describe a male who has an abnormal allele for a gene located on the X chromosome and there is no other copy of the gene?

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

    Why are the terms homozygous, heterozygous, and hemizygous not used to describe genotypes at mitochondrial loci?

    <p>Because mitochondrial DNA molecules are present in tens to thousands of copies per cell</p> Signup and view all the answers

    What is the term used to describe single-gene traits caused by mutations in genes in the nuclear genome?

    <p>Mendelian Inheritance</p> Signup and view all the answers

    What is the usual first step in establishing the pattern of transmission of a single-gene disorder in a family?

    <p>To obtain information about the family history of the patient and summarize the details in the form of a pedigree</p> Signup and view all the answers

    What type of disorders result from a combination of multiple genetic and environmental causes?

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

    What is the term used to describe the family member through whom a family with a genetic disorder is first brought to the attention of the geneticist?

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

    What is the term used to describe disorders in which entire chromosomes (or large segments of them) are missing, duplicated, or otherwise altered?

    <p>Chromosomal Disorders</p> Signup and view all the answers

    What type of disorders are often termed mendelian conditions, or single-gene disorders?

    <p>Disorders in which single genes are altered</p> Signup and view all the answers

    What is the term used to describe the study of the characteristics of garden peas by Gregor Mendel?

    <p>Mendelian Inheritance</p> Signup and view all the answers

    What is the term used to describe well-known examples of single-gene disorders?

    <p>Cystic Fibrosis, Sickle Cell Disease, and Hemophilia</p> Signup and view all the answers

    What is the characteristic of a pure dominant disease?

    <p>Homozygotes and heterozygotes are both affected equally.</p> Signup and view all the answers

    What is the term for the expression of two different alleles for a locus?

    <p>Codominant expression</p> Signup and view all the answers

    What is the characteristic of an incompletely dominant disease?

    <p>Homozygotes are more severely affected than heterozygotes.</p> Signup and view all the answers

    What is the characteristic of a recessive disease?

    <p>The disease is expressed only in homozygotes.</p> Signup and view all the answers

    What is the probability that a gene will have any phenotypic expression at all?

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

    What is the term for the phenomenon where some individuals with the appropriate genotype completely fail to express the phenotype?

    <p>Reduced penetrance</p> Signup and view all the answers

    Why do heterozygotes typically not develop recessive diseases caused by mutations that impair or eliminate enzyme function?

    <p>Because they have one normal allele and one abnormal allele.</p> Signup and view all the answers

    Study Notes

    Patterns of Single-Gene Inheritance

    • Genetic diseases can be classified into three types: single-gene, chromosomal, and complex
    • Single-gene traits are caused by mutations in genes in the nuclear genome and occur in fixed proportions among offspring of specific matings
    • Mendelian inheritance is the study of single-gene traits and their patterns in pedigrees

    Types of Genetic Diseases

    • Single-gene disorders: caused by mutations in genes, often termed Mendelian conditions (e.g., cystic fibrosis, sickle cell disease, and hemophilia)
    • Chromosomal disorders: result from entire chromosomes or large segments being missing, duplicated, or altered (e.g., Down syndrome and Turner syndrome)
    • Multifactorial disorders: result from a combination of multiple genetic and environmental causes

    Mendelian Inheritance

    • Patterns of single-gene inheritance depend on two main factors:
      • Whether the phenotype is dominant (expressed when one chromosome carries the mutant allele) or recessive (expressed only when both chromosomes carry mutant alleles)
      • Chromosomal location of the gene locus (autosome or sex chromosome)
    • There are four basic patterns of single-gene inheritance: autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive

    Autosomal and X-Linked Inheritance

    • Autosomal disorders affect males and females equally
    • X-linked disorders affect males and females differently due to hemizygosity in males and heterozygosity in females
    • Females can be heterozygous or homozygous at X-linked loci, while males are never heterozygous

    Dominant Inheritance

    • A phenotype expressed in both homozygotes and heterozygotes is inherited as a dominant
    • Dominant disorders occur regardless of normal gene product made from the remaining normal allele
    • A person with a pair of identical alleles is homozygous, while a person with different alleles is heterozygous

    Genotype and Phenotype

    • Compound heterozygote: a genotype with two different mutant alleles of the same gene
    • Hemizygous: a male with an abnormal allele for a gene located on the X chromosome and no other copy of the gene
    • Mitochondrial DNA: special case where terms homozygous, heterozygous, and hemizygous are not used to describe genotypes at mitochondrial loci

    Pedigrees

    • Pedigrees are graphical representations of family trees used to establish patterns of transmission in families
    • The extended family depicted in a pedigree is a kindred
    • Proband: the member through whom a family with a genetic disorder is first brought to the attention of the geneticist

    Dominant Inheritance (continued)

    • Pure dominant disease: homozygotes and heterozygotes are affected equally (rare in medical genetics)
    • Codominant: phenotypic expression of two different alleles for a locus (e.g., ABO blood group system)
    • Incompletely dominant: disease is more severe in homozygotes than in heterozygotes

    Recessive Inheritance

    • A phenotype expressed only in homozygotes (or male hemizygotes for X-linked traits) is recessive
    • Most recessive disorders are due to mutations that reduce or eliminate the function of the gene product (loss-of-function mutations)
    • Examples of recessive diseases include those caused by mutations that impair or eliminate enzyme function

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    Related Documents

    Patterns of Single-Gene Inheritance 2024 PDF

    Description

    This quiz covers the basics of single-gene inheritance, including genotype and phenotype, pedigrees, and Mendelian inheritance. It also explores factors affecting pedigree patterns and correlating genotype and phenotype.

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