Final answer:
The primary distinction between different cell types within the same organism lies in the different pattern of gene expression. Cells have the same DNA but read and express distinct sets of genes appropriate to their specialized functions.
Step-by-step explanation:
All cells in a multicellular organism, such as humans, have identical DNA sequences; however, what distinguishes different cell types is the selective expression of different genes. Different gene expression leads to the production of different proteins, which in turn determine the unique functions and characteristics of each cell type. We can think of it like a movie script: all actors have the same script, but each actor only performs their specific part. Similarly, in a cell, the entire genome is present but only specific genes are 'read' or expressed, which is a key factor in cell differentiation and function.
For instance, a skin cell will express genes relevant to protecting the body's surface and would not typically express genes specific to the function of a neuron, which transmits electrical signals in the brain. The regulation of gene expression is highly complex and is controlled at multiple levels in eukaryotic cells, ranging from transcription and mRNA processing to translation and post-translational modifications of proteins. Ultimately, these regulatory mechanisms ensure that each cell type has a distinct role within the organism.