Which of the following most likely accounts for structural and functional differences between the skin cells, smooth muscle cells, and liver cells of the same person?

• A. Differences in gene expression
• B. Differences in DNA sequence
• C. Differences in cell size
• D. Differences in oxygen supply

Answer: (A)

Cells in different tissues become specialized because of which genes are turned on or off. In the same person, all cells share the same DNA, but each cell type expresses a different set of genes, producing the specific proteins and structural components it needs. That’s why skin cells form a protective barrier, liver cells carry out metabolism with particular enzymes, and smooth muscle cells build the contractile machinery for movement. The distinct structures and functions arise from gene expression patterns, not from changes in the DNA sequence itself. While cell size or local oxygen levels can influence how cells operate, they don’t establish the fundamental identity of each tissue type the way selective gene expression does.