In a typical differentiated (specialized) human somatic cell, approximately what percentage of the genome’s genes are actively expressed (transcribed) at any given time?

• A. About 80–90% of genes
• B. About 10–20% of genes
• C. About 1–2% of genes
• D. About 50–60% of genes

Answer: (B)

Verified step by step guidance

1. Understand that gene expression in differentiated human somatic cells is selective, meaning not all genes are active at once because cells specialize in certain functions.
2. Recall that the human genome contains roughly 20,000-25,000 genes, but only a subset is needed for the specific functions of a given cell type at any moment.
3. Recognize that studies using techniques like RNA sequencing show that typically only about 10-20% of genes are actively transcribed in a specialized somatic cell at a given time.
4. Consider that the remaining genes are either silent or expressed at very low levels, as they may be needed only in other cell types or under different conditions.
5. Conclude that the correct estimate for the percentage of genes actively expressed in a typical differentiated human somatic cell at any given time is about 10-20%.