What characterizes the chromatin of the inactive X chromosome?

• A. It is actively transcribed.
• B. It has a high level of expression of genes.
• C. It is highly condensed.
• D. It replicates later than active chromosomes.

Answer: (C)

The chromatin of the inactive X chromosome is characterized by its highly condensed state. In human females, one of the two X chromosomes undergoes a process called X-inactivation, which renders it transcriptionally inactive. This condensation is a key feature of heterochromatin, the form of DNA that is tightly packed and typically not accessible for transcription.

This condensation serves to effectively silence the genes on the inactive X chromosome, preventing their expression. The compact structure of the chromatin results in reduced accessibility for transcription factors and other proteins necessary for gene expression, ensuring that the genes located on the inactive X chromosome are not expressed.

The other aspects of the inactive X chromosome, such as its timing of replication or the level of gene expression, further support its role as a transcriptionally silent entity, but the defining characteristic that stands out is indeed its highly condensed state.