Genetics: Introduction and Disorders
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Genetics: Introduction and Disorders

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Questions and Answers

Which of the following diseases is associated with X-linked dominant inheritance?

  • Cleft lip
  • Rett's syndrome (correct)
  • Hirschsprung disease
  • Diabetes mellitus

    • In X-linked recessive inheritance, a son can be unaffected while his sister is a carrier.

    True

    What type of inheritance involves traits influenced by both genetic and environmental factors?

    Multifactorial inheritance

    Conditions like neural tube defects and diabetes mellitus are examples of __________ inheritance.

    <p>multifactorial/polygenic</p> Signup and view all the answers

    Match the following conditions with their type of inheritance:

    <p>Vitamin D resistant rickets = X-linked dominant Cleft palate = Multifactorial/polygenic Rett's syndrome = X-linked dominant Neural tube defects = Multifactorial/polygenic</p> Signup and view all the answers

    Who coined the term 'genetics'?

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

    Each human cell contains 48 chromosomes.

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

    What determines genetic sex in humans?

    <p>The sex chromosomes (XX for female, XY for male)</p> Signup and view all the answers

    A genetic female has __ sex chromosomes.

    <p>two X</p> Signup and view all the answers

    Which of the following is a type of genetic disorder?

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

    Homozygotes for the dominant gene often survive in utero.

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

    What inheritance pattern results when one out of two homologous genes is sufficient to manifest a disease?

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

    Match the type of genetic disorder with its description:

    <p>Chromosomal disorders = Alteration in chromosome structure or number Single gene disorders = Disorders caused by single gene alteration Multifactorial disorders = Involves multiple genetic and environmental factors</p> Signup and view all the answers

    What is the inheritance pattern of mitochondrial gene mutations?

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

    Sons of an affected female with a mitochondrial disorder can transmit the disease to their offspring.

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

    What condition is characterized by the absence of chromosome 15 from paternal origin?

    <p>Prader Willi syndrome</p> Signup and view all the answers

    A child with both copies of a chromosome from the same parent is said to have __________.

    <p>uniparental disomy</p> Signup and view all the answers

    Match the genetic syndromes with their corresponding chromosomes:

    <p>Beckwith-Wiedemann syndrome = Chromosome 11 Silver-Russell syndrome = Chromosome 7 Prader Willi syndrome = Chromosome 15 (paternal) Angelman syndrome = Chromosome 15 (maternal)</p> Signup and view all the answers

    Which of the following increases the risk of Down syndrome?

    <p>Advanced maternal age</p> Signup and view all the answers

    Down syndrome is caused only by nondisjunction during the formation of maternal gametes.

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

    What percentage of Down syndrome cases are due to Trisomy 21?

    <p>95%</p> Signup and view all the answers

    The term __________ refers to a mixture of normal and abnormal mitochondrial genomes in a cell.

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

    Which type of uniparental disomy features identical chromosomes?

    <p>Uniparental isodisomy</p> Signup and view all the answers

    Which of the following diseases is inherited in an autosomal dominant manner?

    <p>Huntington disease</p> Signup and view all the answers

    In autosomal recessive inheritance, males and females are affected equally.

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

    What is the recurrence risk for parents who have previously had an affected child with an autosomal recessive disorder?

    <p>25%</p> Signup and view all the answers

    Diseases such as hemophilia A and B are inherited in an ______ manner.

    <p>X-linked recessive</p> Signup and view all the answers

    Match the following inherited conditions with their appropriate inheritance pattern:

    <p>Cystic fibrosis = Autosomal recessive Achondroplasia = Autosomal dominant Duchenne's muscular dystrophy = X-linked recessive Fragile X syndrome = X-linked dominant</p> Signup and view all the answers

    An affected male with an X-linked dominant disorder can pass the disorder to which of the following?

    <p>Daughters only</p> Signup and view all the answers

    X-inactivation in females results in the expression of both X chromosomes.

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

    Name one disease that follows an autosomal recessive inheritance pattern.

    <p>Cystic fibrosis</p> Signup and view all the answers

    If a female is a carrier for an X-linked recessive disease, she has a ______ chance of having an affected son.

    <p>25%</p> Signup and view all the answers

    Which of the following is a characteristic of autosomal recessive inheritance?

    <p>Equally affects males and females</p> Signup and view all the answers

    Study Notes

    Genetics: Introduction

    • Genetics deals with the study of genes and their inheritance from parents to offspring.
    • Human cells contain 46 chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes (XY or XX).
    • Chromosomes have a short arm (p) and a long arm (q) connected by the centromere.
    • Genetic sex is determined by the combination of sex chromosomes:
      • One X and one Y chromosome = Genetic male
      • Two X chromosomes = Genetic female

    Genetic Disorders

    • Chromosomal disorders: Caused by alterations in chromosomes, such as deletions, duplications, or numerical abnormalities.
    • Single gene disorders: Caused by alterations in a single gene, following Mendelian inheritance patterns.
    • Multifactorial disorders: Result from combined genetic and environmental factors.

    Autosomal Dominant Inheritance

    • One copy of the dominant gene is sufficient to manifest the disease (heterozygous state expression).
    • Homozygotes for the dominant gene often die prenatally.
    • Characteristics:
      • Affected parent transmits the disease to 50% of offspring.
      • Males and females are equally affected and can both transmit the disorder.

    Autosomal Recessive Inheritance

    • Both copies of the gene must be altered for the disease to manifest (homozygous state expression).
    • Heterozygotes are carriers but do not express the disease.
    • Characteristics:
      • Transmitted in a horizontal pattern (only one generation).
      • Affects males and females equally.
      • Often involves consanguineous marriages.
      • Most inborn errors of metabolism are inherited recessively.

    X-Linked Recessive Inheritance

    • Females are carriers, while males are primarily affected.
    • Affected males transmit the disease to daughters (carriers).
    • Male-to-male transmission is not observed.
    • Examples: Hemophilia A & B, Duchenne's muscular dystrophy, fragile X syndrome.

    X-Linked Dominant Inheritance

    • Males are more severely affected than females.
    • Affected males transmit the disease only to daughters.
    • Examples: Vitamin D resistant rickets, Rett's syndrome.

    X-Inactivation (Lyon Hypothesis)

    • One X chromosome in each female cell is randomly inactivated during early development.
    • This balances X-linked gene expression between males and females.

    Mitochondrial Disorders

    • Mitochondria, and their DNA, are inherited only from the mother.
    • Mutations in mitochondrial DNA can lead to phenotypic defects.
    • Variable clinical manifestations due to heteroplasmy (mixture of normal and abnormal mitochondrial genomes).
    • Both sexes can be affected, all offspring of an affected female will be affected, and daughters will transmit the disease.

    Genomic Imprinting

    • The phenotypic expression of some genes is determined by the parent of origin.
    • One parent's copy of a specific gene is silenced, while the other parent's copy is expressed.
    • Examples:
      • Prader-Willi syndrome (paternal chromosome 15 inactivation).
      • Angelman syndrome (maternal chromosome 15 inactivation).

    Uniparental Disomy (UPD)

    • Offspring inherits two copies of the same chromosome from one parent.
    • Can be isodisomy (identical chromosomes) or heterodisomy (different chromosomes).
    • Examples:
      • Beckwith-Wiedemann syndrome (chromosome 11).
      • Silver-Russell syndrome (chromosome 7).

    Down Syndrome (Trisomy 21)

    • Most common chromosomal disorder.
    • Occurs in 1 per 1000 live births.
    • Extra chromosome 21 can be maternal or paternal origin.
    • Advanced maternal age increases the risk.
    • Cytogenetics:
      • Trisomy 21 (95% of cases): Extra copy of chromosome 21 due to nondisjunction in meiosis I.
      • Translocations (4% of cases): Chromosome 21 is translocated with chromosomes 13, 14, or 15.
      • Mosaicism (1% of cases): Trisomy 21 only present in some cells.

    Examples of Diseases Following Different Inheritance Patterns

    • Autosomal Dominant (AD): Huntington's disease, Marfan's syndrome, neurofibromatosis, familial hypercholesterolemia.
    • Autosomal Recessive (AR): Cystic fibrosis, sickle cell anemia, phenylketonuria.
    • X-Linked Recessive: Hemophilia A & B, Duchenne's muscular dystrophy, color blindness.
    • X-Linked Dominant: Vitamin D resistant rickets, Rett's syndrome.
    • Multifactorial/Polygenic: Neural tube defects, cleft lip/palate, diabetes mellitus.

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    Description

    Explore the basics of genetics, including the structure of chromosomes and genetic inheritance. This quiz covers chromosomal disorders, single gene disorders, and autosomal dominant inheritance patterns. Test your understanding of how genetics influence traits and health.

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