American Society for Clinical Pathology (ASCP) Technologist in Cytogenetics certification (ASCP CG) Practice Test

Which chromosome is notably different between C-banding and G-banding methods?

1. Chromosome 12

2. Chromosome 9

3. Chromosome 5

4. Chromosome 18

The correct answer is: Chromosome 9

The correct answer highlights that chromosome 9 exhibits distinctive characteristics when analyzed using C-banding compared to G-banding techniques. C-banding specifically targets the heterochromatic regions of chromosomes, revealing the centromeric and satellite DNA, while G-banding provides a more comprehensive view of the chromosomal structure, highlighting both the euchromatic and heterochromatic regions. In chromosome 9, the C-banding procedure highlights the presence of a large block of heterochromatin at the centromere, which appears more prominent in C-banding compared to G-banding where the focal bands are less pronounced. This technique can expose variations in the heterochromatin that are less discernible in G-banding. This differential staining is significant for identifying chromosomal abnormalities or variations in chromosome structure. Other chromosomes do not demonstrate such a pronounced difference between these two staining methods, which may lead to more uniform results across the bands observed. Understanding these differences is crucial for cytogenetic analysis, as it aids in the diagnosis and characterization of various genetic disorders.