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

The G-light bands produced by routine GTG banding represent which regions of the chromosome?

1. Inactive regions of the chromosome

2. Gene-poor chromatin regions

3. Early replicating AT-rich DNA

4. Active regions, gene-rich and GC rich DNA

The correct answer is: Active regions, gene-rich and GC rich DNA

The correct understanding of G-light bands produced by routine GTG banding is that they represent active regions of the chromosome, which are typically gene-rich and GC-rich DNA. G-light bands are regions where the chromatin is less condensed during the G1 phase of the cell cycle. This lack of condensation allows for the accessibility of transcription factors and RNA polymerase, facilitating gene expression. In contrast, G-dark bands, which appear during GTG banding, represent more condensed areas of chromatin that are often gene-poor and usually contain heterochromatin, which is typically less transcriptionally active. Since G-light bands are associated with a higher number of genes and associated regulatory elements, they are integral in understanding chromosomal function and genetic expression. Thus, the identification of G-light bands as regions rich in active genetic material aligns with the concept that they harbor regions essential for gene transcription and other vital cellular processes.