Human Genetics Quiz: Chromosomal Abnormalities
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Questions and Answers

What event characterizes Robertsonian translocations?

  • Reciprocal exchange of genetic material between two chromosomes
  • Inversion of a segment within a single chromosome
  • Duplication of an entire chromosome set
  • Nonreciprocal translocation with loss of short arms of acrocentric chromosomes (correct)

    • In human genetics, what does the term 'haploid' (n) specifically refer to?

  • The total number of chromosomes in a somatic cell.
  • The number of autosomes present in a cell.
  • The number of chromosome pairs in a diploid cell.
  • The number of chromosomes in a gamete. (correct)

    • Which of the following is a mechanism that can result in polyploidy?

  • Translocation
  • Trisomy
  • Anaphase lag (correct)
  • Monosomy

    • What is the most common origin of triploidy in humans?

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

    What is the chromosomal designation for a human zygote that is monosomic?

    <p>2n - 1 (A)</p> Signup and view all the answers

    What distinguishes autopolyploidy from allopolyploidy?

    <p>Autopolyploidy involves chromosome duplication within a single species, whereas allopolyploidy results from hybridization between closely related species. (D)</p> Signup and view all the answers

    A human zygote with 69 chromosomes would be classified as:

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

    What meiotic error can lead to a diploid egg instead of a haploid egg, potentially resulting in triploidy after fertilization?

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

    What is the primary consequence of errors in meiosis, such as nondisjunction and anaphase lagging?

    <p>Aneuploidy, where the cell has an abnormal number of chromosomes (B)</p> Signup and view all the answers

    Which meiotic error is often associated with advanced maternal age?

    <p>Premature separation of sister chromatids in Meiosis I (D)</p> Signup and view all the answers

    What distinguishes nondisjunction in meiosis I from nondisjunction in meiosis II?

    <p>Meiosis I involves the failure of homologous chromosomes to separate, while meiosis II involves the failure of sister chromatids to separate. (D)</p> Signup and view all the answers

    Which of the following directly results in a cell with two nuclei?

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

    What is a key characteristic of disorders resulting from unbalanced familial chromosomal abnormalities?

    <p>They are inherited and cause a genetic imbalance in the offspring. (C)</p> Signup and view all the answers

    What is the primary feature of recurrent chromosomal syndromes involving deletions or duplications in genomic hotspots?

    <p>They are caused by repeated deletions or duplications in specific regions of the genome. (A)</p> Signup and view all the answers

    Which of the following best describes the term 'anaphase lagging'?

    <p>The delayed movement of a chromosome during anaphase, leading to unequal chromosome distribution. (C)</p> Signup and view all the answers

    What is the significance of chromosomal and genomic events that reveal genomic imprinting regions?

    <p>They highlight regions where gene expression differs depending on whether genes are inherited from the mother or the father. (D)</p> Signup and view all the answers

    According to theoretical expectations, what proportion of gametes from a rob(14;21) translocation carrier should lead to viable offspring?

    <p>1/3 (C)</p> Signup and view all the answers

    In population studies of rob(14;21) translocation carriers, what approximate percentage of progeny from carrier mothers have unbalanced chromosome complements?

    <p>10%-15% (C)</p> Signup and view all the answers

    Which gamete chromosome complements, arising from Robertsonian translocation rob(14;21), theoretically lead to viable offspring?

    <p>Normal and balanced complements. (A)</p> Signup and view all the answers

    What is the theoretical risk for a Down syndrome child if the mother carries a rob(14;21) translocation?

    <p>1 in 3 (D)</p> Signup and view all the answers

    If a rob(14;21) translocation carrier produces a gamete with both the translocation chromosome and the normal chromosome 21, what is the reciprocal product of this event?

    <p>Chromosome 14 only (B)</p> Signup and view all the answers

    If a rob(14;21) translocation carrier produces a gamete with both the translocation chromosome and chromosome 14, what is the reciprocal product of this event?

    <p>Chromosome 21 only (A)</p> Signup and view all the answers

    What is a Robertsonian translocation?

    <p>rob(14;21) (B)</p> Signup and view all the answers

    Which of the following physical characteristics is commonly observed in infants diagnosed with Edwards syndrome (Trisomy 18)?

    <p>Micrognathia (shortness of the lower jawbone) (C)</p> Signup and view all the answers

    What event must occur prior to duplication or deletion of a gene?

    <p>Breakage within the chromosome. (D)</p> Signup and view all the answers

    What is the approximate percentage of infants with trisomy 18 who survive beyond their first year of life?

    <p>5-10% (C)</p> Signup and view all the answers

    Which of the following is a prenatal ultrasound finding that might raise suspicion for trisomy 18?

    <p>Increased amniotic fluid (Polyhydramnios) (D)</p> Signup and view all the answers

    Which genomic rearrangement is typically less harmful?

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

    When does duplication occur during meiosis?

    <p>In a parent with a translocation, inversion, or isochromosome. (C)</p> Signup and view all the answers

    Apart from advanced maternal age, which of the following maternal age ranges has also been observed in cases of Trisomy 18?

    <p>Mothers as young as 20 (B)</p> Signup and view all the answers

    What is a common mechanism leading to deletions and duplications?

    <p>Unequal crossing over between misaligned homologous chromosomes. (C)</p> Signup and view all the answers

    Which of the following is a common type of anomaly observed in the extremities of infants with Edwards syndrome?

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

    What is the sequence for reverse tandem duplication, given a normal sequence of 123456?

    <p>12344356 (D)</p> Signup and view all the answers

    What is the estimated incidence of Edwards syndrome (Trisomy 18) in live births?

    <p>1 in 6,000 to 8,000 live births (C)</p> Signup and view all the answers

    Which of the following abdominal wall defects is associated with Trisomy 18?

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

    Which of the following changes copy number as a result of genome rearrangements?

    <p>Genes located between the copies of the repeat. (C)</p> Signup and view all the answers

    What is the sequence of tandem duplication, given a normal sequence of 123456?

    <p>12343456 (A)</p> Signup and view all the answers

    What is the likely outcome for pregnancies complicated by Trisomy 18?

    <p>Approximately 95% pregnancies with this anomaly result in fetal death before birth (B)</p> Signup and view all the answers

    Which event is more common during meiosis?

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

    What genetic alteration is primarily associated with DiGeorge syndrome (DGS)?

    <p>Deletion of a 3-Mb region (A)</p> Signup and view all the answers

    How many genes are approximately removed in a typical deletion associated with DiGeorge syndrome?

    <p>30 genes (A)</p> Signup and view all the answers

    What deletion size is observed in about 10% of DiGeorge syndrome patients?

    <p>1.5-Mb deletion (D)</p> Signup and view all the answers

    What is the genetic characteristic of patients with dup(22)(q11.2q11.2)?

    <p>Reciprocal duplication of 22q11.2 (A)</p> Signup and view all the answers

    Cat eye syndrome is associated with which genetic change?

    <p>Tetrasomy for 22q11.2 (A)</p> Signup and view all the answers

    Which aspect is notable about the duplication in patients with cat eye syndrome?

    <p>The duplicated region is inverted relative to other duplications (A)</p> Signup and view all the answers

    Which of the following syndromes is related to deletions in the 22q11.2 region?

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

    What is indicated by the presence of segmental duplications in the genomic region 22q11.2?

    <p>Potential for genomic rearrangements (D)</p> Signup and view all the answers

    Flashcards

    Robertsonian translocation

    A nonreciprocal translocation involving the fusion of the long arms of acrocentric chromosomes and loss of their short arms.

    Haploid

    A cell containing one set of chromosomes (23 in humans).

    Diploid

    A cell containing two sets of chromosomes (46 in humans).

    Triploid

    A condition with three sets of chromosomes (69 in humans).

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    Autopolyploidy

    An increase in the number of chromosome sets within a single species.

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    Allopolyploidy

    An increase in chromosome number due to hybridization between closely related species.

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    Aneuploidy

    A condition where the gamete has an abnormal number of chromosomes, leading to trisomy or monosomy in zygotes.

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    Trisomy

    A chromosomal condition where a zygote has three copies of one chromosome (2n + 1).

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    Abnormal Chromosome Segregation

    Disorders caused by incorrect separation of chromosomes during cell division.

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    Nondisjunction in Meiosis I

    Failure of homologous chromosomes to separate in the first meiotic division.

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    Nondisjunction in Meiosis II

    Failure of sister chromatids to separate in the second meiotic division.

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    Premature separation of sister chromatids

    Early separation of sister chromatids, often due to advanced maternal age.

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    Anaphase Lagging

    When a chromosome fails to move towards the pole during anaphase, causing unequal distribution.

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    Cytokinesis Failure

    Failure of cytoplasm to divide after nuclear division, resulting in one cell with two nuclei.

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    Idiopathic Chromosomal Abnormalities

    Chromosomal abnormalities with an unknown cause that arise spontaneously.

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    Gamete production

    Process of forming reproductive cells from a carrier of a translocation.

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    Balanced complement

    A gamete with the correct number of chromosomes with no genetic imbalance.

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    Unbalanced gametes

    Gametes with an irregular number of chromosomes leading to genetic abnormalities.

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    Chromosome 21

    One of the human chromosomes involved in Down syndrome.

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    Down syndrome risk

    The theoretical chance of having a child with Down syndrome from a carrier.

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    Viable offspring

    Children that can survive and develop normally.

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    Carrier mothers

    Women who carry a translocation and can pass it on to their children.

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    Edwards Syndrome

    A genetic disorder caused by trisomy 18, characterized by severe developmental issues.

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    Common findings in infants

    Infants with Edwards syndrome show growth and anatomical abnormalities, including mental and physical issues.

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    Micrognathia

    A condition where the lower jaw is shorter than usual, often seen in Edwards syndrome.

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    Clenched hand

    A common hand anomaly in trisomy 18 where the fingers are tightly closed.

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    Polyhydramnios

    Excess amniotic fluid around the baby, often associated with higher risks during pregnancy.

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    Omphalocele

    A birth defect causing the baby's intestines to protrude through the abdominal wall.

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    Survival rates

    Only 5-10% of babies with trisomy 18 survive beyond one year due to complications.

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    Incidence of trisomy 18

    Occurs in 1 in 6,000 to 8,000 live births, making it the second most common autosomal trisomy.

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    Deletion Syndrome

    A genetic disorder caused by the loss of a segment of DNA from a chromosome.

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    Duplication Syndrome

    A genetic disorder caused by the presence of extra copies of DNA segments.

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    Unequal Crossing Over

    A process where misaligned chromosomes exchange segments, leading to gene duplications or deletions.

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    Segmentally Duplicated Sequences

    DNA sequences that are repeated within the genome, leading to potential rearrangements.

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    Tandem Duplication

    A type of duplication where a segment of DNA is repeated in sequence, adjacent to the original.

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    Reverse Tandem Duplication

    A type of duplication where the order of copies is reversed.

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    Meiotic Events

    Biological processes during reproduction that can lead to chromosomal duplications or deletions.

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    Genomic Rearrangements

    Alterations in the structure of chromosomes, such as duplications and deletions, affecting gene copy number.

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    22q11.2

    A specific chromosomal region associated with several developmental disorders.

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    DiGeorge syndrome (DGS)

    A disorder caused by deletion of a 3-Mb region on chromosome 22q11.2.

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    Velocardiofacial syndrome (VCFS)

    A genetic disorder linked to a deletion in the 22q11.2 region, similar to DGS.

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    Chromosomal deletion

    A genetic change where a segment of DNA is lost.

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    Reciprocal duplication

    The process where a segment of a chromosome is duplicated and appears twice.

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    Tetrasomy

    A condition with four copies of a particular chromosome region instead of two.

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    Segmental duplications

    Long repeated sequences of DNA that can lead to genetic disorders.

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    Study Notes

    Medical Biology and Genetics: Chromosomal Abnormalities

    • Chromosomal abnormalities encompass a range of genetic disorders arising from numerical or structural changes in chromosomes.
    • Reference materials used for study include Thompson & Thompson Genetics in Medicine (8th Edition).
    • Learning objectives include understanding the genetic basis of numerical and structural syndromes, recognizing clinical features and diagnostic methods, and evaluating treatment options for common syndromes like Down, Turner, and Klinefelter syndromes.

    Terminologies

    • Aneuploidy: An abnormal number of chromosomes in a cell.
    • Trisomy 21 (Down Syndrome): Genetic disorder resulting from an extra copy of chromosome 21.
    • Trisomy 18 (Edwards Syndrome): Genetic disorder resulting from an extra copy of chromosome 18.
    • Trisomy 13 (Patau Syndrome): Genetic disorder resulting from an extra copy of chromosome 13.
    • Uniparental Disomy: A condition where a person inherits two copies of a chromosome from one parent and none from the other.
    • Genomic Disorders (Microdeletion and Microduplication Syndromes): Genetic disorders caused by deletions or duplications of small chromosome segments.
    • Idiopathic Chromosomal Abnormalities: Chromosomal abnormalities with unknown causes.
    • Segregation of Familial Abnormalities: The passing down of chromosomal abnormalities through generations.
    • Genomic Imprinting Disorders: Disorders where gene expression differs depending on whether a gene is inherited from the mother or father.
    • Hydrops: Swelling of the entire body due to heart failure.
    • Micrognathia: Shortness of the lower jaw.
    • Microcephaly: Smaller than normal head size.
    • Omphalocele: Intestines protruding from an opening in the abdominal wall.
    • Polyhydramnios: Excessive amniotic fluid.

    Mechanisms of Chromosomal Abnormalities

    • Numerical Abnormalities:
      • Polyploidy (multiple chromosome sets)
      • Aneuploidy (abnormal chromosome number)
        • Sex chromosome aneuploidy
        • Autosomal aneuploidy
    • Structural Abnormalities:
      • Deletion
      • Duplication
      • Inversion
      • Insertion
      • Ring chromosome
      • Isochromosome
      • Translocations (Robertsonian and Reciprocal)
      • Mosaicism (presence of both normal and abnormal cells)

    Structural Chromosomal Abnormalities

    • Involving Single Chromosomes:
      • Terminal deletion
      • Interstitial deletion
      • Duplication
      • Inversion
      • Insertion
      • Isochromosome
    • Involving Two Chromosomes:
      • Translocations (Robertsonian and Reciprocal)
      • Ring chromosome

    Polyploidy

    • Autopolyploidy: Increase in chromosome sets within a species.
    • Allopolyploidy: Increase in chromosome number due to hybridization between closely related species.
    • Mechanisms of Polyploidy:
      • Anaphase Lag
      • Endoreduplication
      • Failure of cytokinesis

    Triploidy

    • Triploidy is a chromosomal abnormality characterized by the presence of three sets of chromosomes (69 for humans).
    • Most cases result in spontaneous abortion.
    • Triploidy typically results from dispermy or errors in meiosis leading to a diploid egg.

    Aneuploidy

    • Aneuploidy is a condition with an abnormal number of chromosomes either missing or extra copies.
    • Examples: Trisomy (extra copy of a chromosome), Monosomy (missing a copy of a chromosome).
    • Types: Partial and Mosaic (variations in the proportion of normal/abnormal cells).

    Trisomic and Other Common Syndromes

    • Trisomy 21 (Down Syndrome): Significant incidence, distinct clinical features (hypotonia, facial features, intellectual disability).
    • Trisomy 18 (Edwards Syndrome): Severe developmental problems, low survival rates.
    • Trisomy 13 (Patau Syndrome): Similar to Trisomy 18 in severity, low survival rates.
    • Other Syndromes: Klinefelter Syndrome (extra X chromosome in males), Turner Syndrome (missing or incomplete X chromosome in females), Cri du Chat Syndrome (deletion of chromosome 5), Wolf-Hirschhorn Syndrome (deletion of chromosome 4).

    Mechanisms of Chromosomal Abnormalities (Summary)

    • Segregation Errors: Nondisjunction (failure of homologous or sister chromatids to separate properly during meiosis) and Anaphase Lagging.
    • Chromosomal Rearrangements: Deletions, duplications, inversions, and translocations (structural alterations).

    Risk Factors and Diagnostics

    • Maternal age is a primary risk factor for certain chromosomal abnormalities.
    • Prenatal diagnostics like karyotype, chromosomal microarray analysis, and non-invasive prenatal screening aid in diagnosis.
    • Factors like the parents' karyotypes also influence the risk for recurrent abnormalities.

    Additional Syndromes and Anomalies

    • Deletions: 1p36 deletion syndrome, Cri du Chat Syndrome, 4p-deletion syndrome (Wolf-Hirschhorn Syndrome).
    • Duplications: Various duplications of chromosomal regions exist.
    • Isochromosomes: Abnormal chromosomes, consisting of two copies of a single (either p or q) arm.
    • Ring Chromosomes: Abnormal chromosomes, resulting from the fusion of broken ends.

    Further Study/References

    • Specific details of individual syndromes and their associated characteristics, treatment approaches, and recurrence risks should be reviewed from appropriate sources (like the referenced textbook mentioned earlier).

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    Medical Biology and Genetics (Chromosomal Abnormalities) PDF

    Description

    Test your knowledge on human genetics and chromosomal abnormalities with this quiz. Explore key concepts such as Robertsonian translocations, haploidy, and mechanisms leading to polyploidy. Understand the implications of meiotic errors and their consequences on human zygotes.

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