clinical cytogeneticist Interview Questions and Answers

1. What is a karyotype and how is it used in clinical cytogenetics?

   • Answer: A karyotype is a visual representation of a complete set of chromosomes from a cell. It's used to detect chromosomal abnormalities such as aneuploidy (extra or missing chromosomes), translocations (chromosome rearrangements), deletions, and insertions. This information is crucial in diagnosing genetic disorders, cancers, and infertility.

2. Describe the different cytogenetic techniques used in a clinical laboratory.

   • Answer: Common techniques include karyotyping (conventional cytogenetics), fluorescence in situ hybridization (FISH), comparative genomic hybridization (CGH), and array comparative genomic hybridization (aCGH). Karyotyping provides a whole-chromosome view, FISH targets specific sequences, CGH detects copy number changes, and aCGH offers higher resolution than CGH, detecting smaller changes.

3. Explain the process of preparing a sample for karyotype analysis.

   • Answer: The process involves collecting a sample (blood, amniotic fluid, bone marrow, etc.), culturing the cells to stimulate division, arresting them in metaphase (when chromosomes are condensed), harvesting the cells, staining them (e.g., Giemsa banding), and analyzing the resulting chromosomes under a microscope to create a karyotype.

4. What are the limitations of conventional karyotyping?

   • Answer: Karyotyping has a limited resolution; it may miss small deletions, insertions, or subtle rearrangements. It also requires actively dividing cells, which may not always be available. The process is time-consuming compared to newer molecular techniques.

5. How does FISH work and what are its clinical applications?

   • Answer: FISH uses fluorescently labeled DNA probes that bind to specific chromosomal regions. The location and intensity of the fluorescence signal reveal the presence or absence of the target sequence, allowing for the detection of specific chromosomal abnormalities, such as aneuploidy or translocations, even in non-dividing cells. Clinical applications include prenatal diagnosis, cancer diagnosis, and detection of microdeletions/microduplications.

6. What is comparative genomic hybridization (CGH) and how does it differ from array CGH?

   • Answer: CGH compares the DNA copy number of a test sample to a reference sample. Array CGH uses a microarray with thousands of DNA probes to detect copy number variations at a much higher resolution than traditional CGH. Array CGH can identify smaller genomic imbalances and is more sensitive.

7. Explain the significance of banding techniques in karyotyping.

   • Answer: Banding techniques, like G-banding, create a pattern of light and dark bands on chromosomes, allowing for the identification of individual chromosomes and the detection of structural abnormalities. Different banding techniques (e.g., Q-banding, R-banding) provide different banding patterns, enhancing the ability to detect various chromosomal abnormalities.

8. Describe the common chromosomal abnormalities associated with Down syndrome, Turner syndrome, and Klinefelter syndrome.

   • Answer: Down syndrome is typically caused by trisomy 21 (three copies of chromosome 21). Turner syndrome is caused by monosomy X (only one X chromosome in females). Klinefelter syndrome is characterized by an extra X chromosome in males (XXY).

9. How do you interpret a karyotype report?

   • Answer: A karyotype report provides a description of the chromosome number and structure. Interpretation involves understanding the nomenclature (e.g., 47,XX,+21 for Down syndrome), identifying numerical and structural abnormalities, and correlating these findings with the patient's clinical presentation and medical history.

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