Genetics Chapter: Autosomal Disorders Quiz
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Questions and Answers

What is the most likely reason why individuals with new mutations in their germ cells do not have affected parents?

  • The mutation was inherited from a parent, but the penetrance of the disorder is variable.
  • The mutation occurred spontaneously in the egg or sperm that gave rise to the individual. (correct)
  • The mutation occurred in a previous generation, but the parent was a carrier.
  • The mutation occurred in a somatic cell of a parent, not a germ cell.

    • Which of the following is NOT an example of an autosomal dominant disorder?

  • Hereditary spherocytosis
  • Huntington's disease
  • Familial hypercholesterolaemia
  • Sickle cell anemia (correct)

    • A patient with a new mutation for a specific autosomal dominant disorder will likely have:

  • The disorder is unlikely to be passed on to their children unless their partner is also a carrier.
  • The disorder will be more severe than if it were inherited from a parent.
  • They will be the only one in their family tree with the disorder.
  • All of their siblings will also have the disorder.
  • None of these. (correct)

    • Which of these concepts describe a single gene mutation resulting in multiple phenotypic effects?

    <p>Pleiotropy (D)</p> Signup and view all the answers

    What is the most likely reason for the varied clinical features observed in patients with autosomal dominant disorders?

    <p>All of the above. (D)</p> Signup and view all the answers

    A patient with familial hypercholesterolaemia inherits a mutated gene from their parent. This patient has a 50% chance of transmitting the disorder to their children. What concept does this illustrate?

    <p>Penetrance (C)</p> Signup and view all the answers

    Why is it important to distinguish between autosomal dominant and autosomal recessive disorders?

    <p>All of the above. (D)</p> Signup and view all the answers

    Which of these is NOT a potential consequence of a frame-shift mutation?

    <p>All of the above. (E)</p> Signup and view all the answers

    Which of the following diseases is an example of autosomal recessive disorders?

    <p>Phenylketonuria (A)</p> Signup and view all the answers

    Which of the following is true regarding X-linked diseases?

    <p>Transmitted by heterozygous female carriers only to hemizygous sons (C)</p> Signup and view all the answers

    Which of the following conditions is inherited via multifactorial inheritance?

    <p>Diabetes mellitus (A)</p> Signup and view all the answers

    Which of the following statements accurately describes multifactorial inheritance?

    <p>A combination of genetic and environmental influences (D)</p> Signup and view all the answers

    Which of the following is NOT an example of an X-linked disorder?

    <p>Albinism (C)</p> Signup and view all the answers

    What is the definition of aneuploidy?

    <p>A number of chromosomes not an exact multiple of the haploid number (C)</p> Signup and view all the answers

    Which scenario exemplifies nondisjunction during meiosis?

    <p>One gamete with two identical chromosomes is formed (C)</p> Signup and view all the answers

    What is characteristic of Down's syndrome?

    <p>95% of cases result from nondisjunction during meiosis (C)</p> Signup and view all the answers

    Which of the following syndromes is most commonly associated with the karyotype 47, XXY?

    <p>Klinefelter syndrome (A)</p> Signup and view all the answers

    Which condition may arise as a result of polyploidy?

    <p>Triploidy or 3N (B)</p> Signup and view all the answers

    What is a common clinical finding associated with Edward syndrome?

    <p>Overlapping flexed fingers (A)</p> Signup and view all the answers

    Which type of chromosomal aberration is characterized by the presence of an extra chromosome?

    <p>Aneuploidy (B)</p> Signup and view all the answers

    What is commonly observed in patients with Klinefelter syndrome?

    <p>Elevated FSH and LH levels (B)</p> Signup and view all the answers

    Which clinical finding is NOT typically associated with low levels of testosterone?

    <p>Short stature (B)</p> Signup and view all the answers

    What is the main characteristic distinguishing Turner’s syndrome from other forms of hypogonadism?

    <p>Monosomy of the X chromosome (B)</p> Signup and view all the answers

    Which of the following structural chromosomal abnormalities involves no change in the total number of genes?

    <p>Balanced translocation (C)</p> Signup and view all the answers

    Which syndrome is specifically associated with the short arm deletion of chromosome 5?

    <p>Cri du chat syndrome (D)</p> Signup and view all the answers

    What type of translocation occurs when genetic material is exchanged between two non-homologous chromosomes?

    <p>Balanced reciprocal translocation (D)</p> Signup and view all the answers

    Which of the following features is characteristic of Turner’s syndrome?

    <p>Webbing of the neck (C)</p> Signup and view all the answers

    What is the likely result of an unbalanced reciprocal translocation?

    <p>Increased risk of infertility (C)</p> Signup and view all the answers

    What condition arises from the fusion of two acrocentric chromosomes at the centromere?

    <p>Robertsonian translocation (B)</p> Signup and view all the answers

    What is the term for a complete absence of an organ during development?

    <p>Agenesis (C)</p> Signup and view all the answers

    Which of the following is NOT considered a multifactorial inheritance disorder?

    <p>Thalidomide malformations (A)</p> Signup and view all the answers

    Which teratogen is specifically implicated in causing phocomelia?

    <p>Thalidomide (D)</p> Signup and view all the answers

    How are chromosomes classified based on the location of the centromere?

    <p>Metacentric, submetacentric, acrocentric (B)</p> Signup and view all the answers

    What is teratology concerned with?

    <p>Developmental defects due to prenatal factors (D)</p> Signup and view all the answers

    Which technique is used to analyze chromosomes during the metaphase stage?

    <p>Karyotyping using colchicine (A)</p> Signup and view all the answers

    Cleft lip is categorized as which type of developmental defect?

    <p>Malformation (C)</p> Signup and view all the answers

    Which chromosomal banding technique uses Giemsa stain?

    <p>G-banding (C)</p> Signup and view all the answers

    Flashcards

    Developmental defects

    Anomalies resulting from errors in morphogenesis during fetal life.

    Teratology

    The science that studies developmental defects and their causes, particularly teratogens.

    Teratogens

    Agents like chemicals or drugs that cause developmental defects in embryos.

    Agenesis

    The complete absence of an organ that should normally be present.

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    Aplasia

    Absence of development of an organ but presence of rudimentary material.

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    Hypoplasia

    Incomplete development of an organ, leading to smaller size.

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    Karyotyping

    The process of studying chromosomes by arranging them in pairs based on size and shape.

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    G-banding

    A technique used in karyotyping to stain chromosomes, revealing unique dark and light bands.

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    Low testosterone symptoms

    Clinical findings include testicular atrophy, infertility, gynecomastia, and more.

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    Turner's syndrome

    A condition caused by X chromosome loss, leading to female hypogonadism.

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    Primary amenorrhea

    The failure to start menstruation by age 15, commonly seen in Turner’s syndrome.

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    Gynecomastia

    Development of breast tissue in males, often linked to hormonal imbalances.

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    Chromosomal abnormalities

    Structural anomalies that can occur during cell division, potentially affecting offspring.

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    Balanced translocation

    A chromosomal rearrangement maintaining total genetic material, often without observable effects.

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    Robertsonian translocation

    Fusion of acrocentric chromosomes, resulting in one large and one small chromosome.

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    Cri du chat syndrome

    A genetic disorder caused by deletion in chromosome 5, leading to a distinct cry in affected infants.

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    Haploid

    A single set of chromosomes characteristic of a species, e.g. 23 in humans.

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    Diploid

    A double set of chromosomes (2n), e.g. 46 in humans.

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    Euploid

    Any multiple (from n to 8n) of the haploid number of chromosomes.

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    Polyploidy

    A chromosome number that is a multiple of the haploid number, e.g. triploidy (3N) or tetraploidy (4N).

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    Aneuploidy

    A chromosome number that is not an exact multiple of the haploid number, e.g. monosomy (2N-1) or trisomy (2N+1).

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    Down’s syndrome

    A genetic disorder caused by trisomy 21, often resulting from nondisjunction during meiosis.

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    Klinefelter’s syndrome

    A condition in males caused by an extra X chromosome (47, XXY), leading to testicular dysgenesis.

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    Edward syndrome

    A condition caused by trisomy 18, associated with severe developmental issues.

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    Familial polyposis

    A genetic condition characterized by multiple polyps in the colon, increasing cancer risk.

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    X-linked disorders

    Diseases linked to genes on the X chromosome, often inherited from a carrier mother.

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    Autosomal recessive diseases

    Diseases requiring two copies of the mutated gene for symptoms to appear, often seen in metabolic disorders.

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    Multifactorial inheritance

    Inheritance affected by both genetic and environmental factors, not strictly Mendelian.

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    Common X-linked recessive disorders

    Includes conditions like hemophilia and color blindness, primarily affecting males.

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    Mendelian disorders

    Diseases caused by a mutation in a single gene, often inherited.

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    Point mutation

    A change in a single nucleotide in DNA, altering one amino acid.

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    Stop codon mutation

    A mutation that prematurely ends protein synthesis.

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    Frame shift mutation

    Insertion or deletion of bases in DNA, altering the reading frame.

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    Trinucleotide repeat mutations

    Amplification of a sequence of three nucleotides in DNA.

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    Autosomal dominant disorders

    Disorders expressed when only one copy of the mutated gene is present.

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    Reduced penetrance

    Not all individuals with a mutation show the associated trait.

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    Variable expressivity

    Variation in how a phenotype manifests among individuals with the same genotype.

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    Study Notes

    Genetic and Pediatric Diseases

    • Developmental Defects are caused by errors in morphogenesis during fetal life.
    • Teratology is the science dealing with these anomalies.
    • Implicated agents include certain chemicals, drugs, and physical and biological agents (teratogens).
    • The resultant defect is called malformation.
    • Outcomes might include intrauterine fetal death, intrauterine growth retardation, functional defects, or malformations.
    • Teratogens impact differently based on individual susceptibility, exposure trimester (first trimester most susceptible), dose, and specificity of the defect for the specific teratogen.
    • Classifications of defects include a complete absence of an organ (agenesis), absence of development with a rudiment or anlage present (aplasia), incomplete development of an organ (hypoplasia), and incomplete formation of a lumen (atresia).
    • Examples include anencephaly-spina bifida complex, thalidomide malformations (e.g., phocomelia), fetal hydantoin syndrome, fetal alcohol syndrome, TORCH complex (toxoplasmosis, rubella, cytomegalovirus, and herpes simplex) exposure during pregnancy, and congenital syphilis (Hutchison's triad).

    Cytogenetic Abnormalities

    • Ova and sperm contain 23 chromosomes (haploid).
    • Body cells contain 23 pairs of chromosomes (diploid).
    • Lymphocytes are used to study chromosomes.
    • Karyotyping arrests cells in metaphase using colchicine.
    • Cells are spread on a glass slide and stained with Giemsa stain.
    • Chromosomes are classified by centromere location (metacentric, submetacentric, acrocentric).
    • Chromosomal banding (e.g., G-banding, Q-banding, R-banding, C-banding) is used to study chromosomes.

    Numerical Abnormalities

    • Haploid: a single set of chromosomes (23 in humans).
    • Diploid: a double set of chromosomes (46 in humans).
    • Euploid: any multiple of the haploid number (e.g., triploid, tetraploid).
    • Polyploidy: a multiple of the haploid number. This can occur normally in some cell types (e.g., megakaryocytes, liver cells), but in somatic cells of a fetus may result in spontaneous abortion.
    • Aneuploidy: not an exact multiple of the haploid number (e.g., monosomy, trisomy).
    • Nondisjunction (failure of chromosome separation during meiosis or mitosis) is a common cause of aneuploidy. This may also include nullisomy.

    Syndromes arising from chromosomal aberrations

    • Down syndrome (Trisomy 21): 95% of cases due to nondisjunction during meiosis; common cause of mental retardation, higher incidence in mothers over 35.

    • Translocations: some cases of Down Syndrome result from a translocation.

    • Edward syndrome (Trisomy 18): increased incidence with mother's age; caused by nondisjunction; various clinical findings including mental retardation, low-set ears, micrognathia, congenital heart defects, overlapping flexed fingers

    Single Gene Defects

    • These are also called Mendelian disorders.
    • These result from mutation of a single gene.
    • Germ cell mutations cause inherited diseases.
    • Somatic cell mutations cause cancer or congenital malformations.
    • Types of mutations include: point mutations (substitution of one nucleotide base), stop codon/nonsense mutations (premature termination of protein chain); frame-shift mutations (insertion/deletion of one or two base pairs), and trinucleotide repeat mutations (amplification of sequence of 3 nucleotides)

    Mendelian Disorders

    • Caused by single gene defects.
    • Mutations can be autosomal dominant, autosomal recessive, or sex-linked.
    • A single gene mutation can lead to multiple phenotypic effects (pleiotropy).
    • Mutations at multiple genetic loci can produce the same trait (heterogeneity).

    Autosomal Dominant Disorders

    • Manifested in the heterozygote state.
    • One affected parent often has an affected child.
    • Males and females can be affected.
    • Affected individuals can pass the condition to their children.
    • In heterozygote x unaffected marriage, the child has a 50% chance of inheriting the condition.
    • Some patients have the condition due to new mutations, and sibling risk may not be increased by the individual's condition.
    • Age of symptom onset may sometimes be delayed.
    • Examples include Familial hypercholesterolaemia, Adult Polycystic kidney disease, Huntington's disease, familial polyposis coli, hereditary spherocytosis, and Marfan's syndrome.

    Autosomal Recessive Disorders

    • Examples include inborn errors of metabolism such as phenylketonuria and alkaptonuria; lysosomal storage diseases such as glycogenosis and including lipidoses.
    • Endocrine diseases, such as congenital adrenal hyperplasia.
    • Nervous system disorders, such as neurogenic muscular atrophies, Friedreich ataxia, and spinal muscular atrophy.

    Sex-Linked Disorders

    • All examples are X-linked.
    • No known Y-linked disorders.
    • Most are X-linked recessive.
    • Transmitted by heterozygous female carriers to sons who are hemizygous for the X-chromosome.
    • Examples include musculoskeletal disorders such as Duchenne muscular dystrophy, blood disorders such as haemophilia A and B, immune disorders such as agammaglobulinaemia, and metabolic disorders such as diabetes mellitus.

    Diseases with Multifactorial Inheritance

    • Combined effect of genetic and environmental influences.
    • Examples include cleft lip and cleft palate, pyloric stenosis, diabetes mellitus, hypertension, congenital heart disease, and peptic ulcer.

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    Test your knowledge on autosomal dominant and recessive disorders with this quiz. Explore concepts such as mutations, inheritance patterns, and their implications in clinical features. Perfect for students studying genetics or related fields!

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