What is a laboratory test that examines chromosomes in cells to identify numerical or structural abnormalities?

• A. Cytogenetic analysis
• B. Chromosomal microarray
• C. Flow cytometry
• D. PCR assay

Answer: (A)

The key idea is directly visualizing the chromosomes to detect changes in number or structure. Cytogenetic analysis does this by examining chromosomes in cultured cells, often as metaphase spreads, using banding techniques (like G-banding) or targeted probes. This approach reveals the overall chromosome complement (showing numerical changes such as extra or missing chromosomes) and large structural rearrangements (translocations, deletions, duplications, inversions). That direct, genome-wide view is what makes it the best fit for identifying both numerical and structural chromosome abnormalities.

Chromosomal microarray, while very good at finding small copy-number changes, often misses balanced rearrangements and the overall chromosome count. Flow cytometry analyzes cell properties such as size and granularity, not chromosome structure. PCR assays amplify specific DNA regions and aren’t used for surveying whole chromosomes for number or large structural changes.