Ch.8 Chromosomal Structure & Chromosomal Mutations

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  1. What chromosomal location is indicated by 15q21.1?
    This location is on the long arm of chromosome 15, region 2, band 1, sub-band 1.
  2. During interphase FISH analysis for the t(9;22) translocation, one nucleus was observed with two normal signals (one red for chromosome 22 and one green for chromosome 9) and one compositered/green signal.

    Five hundred other nuclei were normal.

    What is one explanation for this observation?
    Since only 1 of 500 cells showed the composite signal, this observation may be due to overlap of the chromosomes on the slide, rather than atranslocation. The presence of a translocation,however, cannot be ruled out.
  3. Is 47;XYY a normal karyotype?
    This is not a normal karyotype. Thereare two Y chromosomes.
  4. Write the numerical and structural chromosomal abnormalities represented by the following genotypes:

    47,XY, +18
    46, XY,del(16)p(14)
    46,XX del(22)q(11.2)
    47,XY, +18 — trisomy 18.

    46,XY, del(16)p(14) — deletion in the short arm of chromosome 16 at region 1, band 4.

    iso(Xq) — isochromosome formed by centromericjoining of two long arms of the X chromosome.

    46,XX del(22)q(11.2) — a deletion in the long arm qof chromosome 22 at region 1, band 1, sub-band 2.

    45,X — deletion of one of the X or the Ychromosome.
  5. A chromosome with a centromere located such that one arm of the chromosome is longer than the other arm, is called

    a. metacentric
    b. paracentric
    c. telocentric
    d. submetacentric

    A chromosome with a long and shortarm is submetacentric (d).
  6. A small portion from the end of chromosome 2 has been found on the end of chromosome 15, replacing the end of chromosome 15, which has moved to the end of chromosome 2.

    This mutation is called a

    a. reciprocal translocation
    b. inversion
    c. deletion
    d. robertsonian translocation
    Exchange of portions of chromosomes with no loss of genetic material is a reciprocal translocation (a).
  7. Phytohemagglutinin is added to a cell culture when preparing cells for karyotyping. The purpose of the phytohemagglutinin treatment is to

    a. arrest the cell in metaphase
    b. spread out the chromosomes
    c. fix the chromosomes on the slide
    d. stimulate mitosis in the cells
    Phytohemagglutinin is a mitogen that stimulates mitosis in the cells (d).
  8. A centromeric probe is used to visualize chromosome 21.

    Three fluorescent signals are observed in the cell nuclei when stained with this probe. The seresults would be interpreted as consistent with

    a. a normal karyotype
    b. Down syndrome
    c. Klinefelter syndrome
    d. technical error
    Down syndrome results from trisomy 13,which would lead to the observation above (b).
  9. Cells were harvested from a patient’s blood, cultured to obtain chromosomes in metaphase, fixed onto a slide, treated with trypsin, and then stained with Giemsa. The resulting banding pattern is called

    a. G banding
    b. Q banding
    c. R banding
    d. C banding
    The reproducible patterns in Giemsa stained chromosomes is called G-banding.
  10.  A FISH test with a centromere 13 probe is ordered for a suspected case of Patau syndrome (trisomy 13).

    How many signals per nucleus will result if the test is positive for Patau syndrome?
    The FISH results would reveal three signals per nucleus with a probe to centromere 13.
  11. What would be the results if a centromere 13 probe was used on a case of Edward syndrome (trisomy 18)? 
    The FISH results would reveal two signals per nucleus with a probe to centromere 13.

    A probe to centromere 18 would yield three signals per nucleus.
  12. Angelman syndrome is caused by a microdeletion in chromosome 15.

    Which method, karyotyping or metaphase FISH, is better for accurate detection of this abnormality?

    Metaphase FISH is preferred for detection of microdeletions. The lower resolution of karyotyping makes detection of small deletions difficult.
  13. The results of a CGH analysis of Cy3 (green)-labeled test DNA with Cy5 (red)-labeled reference DNA on a normal chromosome spread revealed a bright red signal along the short arm of chromosome 3.

    How is this interpreted?

    a. 3p deletion
    b. 3q deletion
    c. 3p amplification
    d. 3q amplification
    The red signal from the reference chromosome region indicates a loss or deletion of thetest chromosome 3p (a).
  14. A break-apart probe is used to detect a translocation.The results of FISH analysis show two signals in70% of the nuclei counted and three signals in 30% of the nuclei.

    Is there a translocation present?
    A translocation is present, indicated by the cells in which three signals appear. The probe spans the translocation breakpoint, producing two separate signals when a translocation occurs. The third signal in these cells is the intact homologous chromosome.
  15. What FISH technique is most useful for detection of multiple complex genomic mutations?
    Spectral karyotyping labels each chromosome with a different fluorescent color so that multiple complex genomic mutations are clearly identified.
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Ch.8 Chromosomal Structure & Chromosomal Mutations
Buckingham & Flaws Ch.8 Chromosomal Structure & Chromosomal Mutations Q&A
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