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Cytogenetics and Chromosomal Analysis Flashcards

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  1. A copy number variant (CNV) is generally defined as a segment of DNA greater than how many base pairs that shows variation in copy number relative to a reference genome?

    Answer: 1,000 bp (1 kb)

    CNVs are conventionally defined as segments ≥1 kb (1,000 bp) that are present at variable copy numbers compared to a reference genome, distinguishing them from smaller insertion/deletion variants.

  2. Which prenatal cytogenetic technique provides the earliest diagnostic result for chromosomal abnormalities, typically performed at 10–13 weeks gestation?

    Answer: Chorionic villus sampling (CVS)

    CVS is performed at 10–13 weeks and provides fetal chromosomal material earlier than amniocentesis (15–20 weeks) or cordocentesis (18+ weeks).

  3. In cancer cytogenetics, a deletion of 17p13.1 is most associated with loss of function of which tumor suppressor gene?

    Answer: TP53

    TP53, which encodes the p53 tumor suppressor protein, is located at 17p13.1, and its deletion or mutation is one of the most common alterations across many cancers.

  4. Chromosomal instability syndromes such as Bloom syndrome, Fanconi anemia, and ataxia-telangiectasia share which cytogenetic hallmark?

    Answer: Increased frequency of chromosomal breaks and rearrangements

    These syndromes are caused by defects in DNA repair pathways, resulting in elevated rates of chromosomal breaks, sister chromatid exchanges, and structural rearrangements detectable cytogenetically.

  5. When reporting a Robertsonian translocation between chromosomes 13 and 14, the correct ISCN notation for a carrier with 45 chromosomes is:

    Answer: 45,XY,rob(13;14)(q10;q10)

    ISCN uses rob() to denote Robertsonian translocations; 45,XY,rob(13;14)(q10;q10) correctly indicates a male carrier with 45 chromosomes due to fusion of acrocentric chromosomes 13 and 14 at their centromeres.

  6. Constitutional chromosomal abnormalities differ from somatic (acquired) chromosomal changes primarily in that constitutional changes are:

    Answer: Present in every nucleated cell of the body and inherited through the germline

    Constitutional chromosomal abnormalities arise during gametogenesis or early embryogenesis and are therefore present in virtually every cell of the body, whereas somatic changes arise post-zygotically in specific tissues.

  7. Which chromosomal microarray platform approach is required by ACMG guidelines for the evaluation of individuals with unexplained developmental delay, intellectual disability, autism spectrum disorder, or multiple congenital anomalies?

    Answer: Chromosomal microarray analysis (CMA) as a first-tier test

    ACMG recommends CMA as the first-tier cytogenetic diagnostic test for individuals with unexplained DD/ID, ASD, or MCA because it detects submicroscopic CNVs missed by conventional karyotyping.