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Cytogenetics and Chromosomal Analysis Flashcards

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  1. Which banding technique is most commonly used to produce a standard karyotype in clinical cytogenetics laboratories?

    Answer: G-banding

    G-banding (Giemsa banding) is the standard technique used in clinical cytogenetics to produce a karyotype with characteristic dark and light band patterns.

  2. According to the ISCN (International System for Human Cytogenomic Nomenclature), how is a male with trisomy 21 correctly written?

    Answer: 47,XY,+21

    47,XY,+21 indicates a male (XY) with 47 total chromosomes due to an extra chromosome 21, which is the correct ISCN notation for Down syndrome in a male.

  3. Fluorescence in situ hybridization (FISH) is best suited for detecting which type of chromosomal abnormality?

    Answer: Submicroscopic deletions at targeted loci

    FISH uses locus-specific probes to detect submicroscopic deletions or duplications at targeted regions that are too small to be seen by conventional karyotyping.

  4. A chromosomal microarray (CMA) using SNP probes has an advantage over array CGH in that it can detect:

    Answer: Uniparental disomy (UPD)

    SNP-based arrays can identify stretches of homozygosity that indicate uniparental disomy, which array CGH cannot detect because UPD does not involve copy number change.

  5. The most common cause of trisomy 21 (Down syndrome) is:

    Answer: Meiotic nondisjunction

    Approximately 95% of Down syndrome cases result from meiotic nondisjunction, most often in maternal meiosis I, leading to a gamete with two copies of chromosome 21.

  6. Turner syndrome (45,X) most commonly results from loss of the sex chromosome derived from which parent?

    Answer: Maternal X is retained; paternal sex chromosome is lost

    Studies show that in ~75% of 45,X cases the retained X is of maternal origin, meaning the paternal sex chromosome (X or Y) was lost.

  7. Fragile X syndrome is caused by a CGG trinucleotide repeat expansion in the promoter region of which gene?

    Answer: FMR1

    Fragile X syndrome results from a >200 CGG repeat expansion (full mutation) in the 5' UTR of FMR1 on the X chromosome, leading to gene silencing via methylation.