Final answer:
Euchromatin is the type of DNA that produces a light band when it is stained with Giemsa stain, indicating regions of actively transcribed genes due to its less condensed structure.
Step-by-step explanation:
The type of DNA that produces a light band when treated with Giemsa stain is euchromatin. Euchromatin is less densely packed compared to heterochromatin and usually contains genes that are being actively transcribed. During interphase, euchromatin regions are not compacted as tightly as heterochromatin, allowing for greater accessibility for the transcription machinery.
Heterochromatin, on the other hand, usually contains genes that are not actively transcribed and tends to stain darkly with Giemsa stain due to its tighter packaging. This tightly packed DNA is commonly found around centromeres and telomeres. The less condensed nature of euchromatin leads to the formation of lighter bands, which indicates regions where genes are potentially active and transcription can occur.