What is one of the characteristics of G-dark bands in chromosome analysis?

G-dark bands are a feature observed during Giemsa staining of chromosomes. These bands are typically regions of the chromosome that are densely packed with chromatin and correlate with heterochromatin. Heterochromatin is generally transcriptionally inactive, meaning it is less involved in the expression of genes compared to euchromatin, which is less condensed and actively transcribes genes. The presence of G-dark bands indicates areas of the chromosome that are rich in repetitive sequences and are generally more condensed than their euchromatic counterparts.

The other characteristics described in the options do not apply to G-dark bands. For example, euchromatin is associated with lighter bands in Giemsa staining, indicating active transcription, while early replicating regions are typically found in lighter bands (euchromatin). Furthermore, G-dark bands are present throughout the entire cell cycle, not limited to meiosis, meaning their visibility is not restricted to one phase of cell division. Hence, the defining characteristic of G-dark bands as corresponding to heterochromatin correctly encapsulates their nature in chromosome analysis.