Final answer:
A gene is the part of a DNA strand that produces a protein leading to stem cell differentiation, with transcription factors being critical in this process.
Step-by-step explanation:
The term for the part of a DNA strand that produces a protein which causes a stem cell to differentiate is a gene. Genes are units of DNA that contain the code for creating specific proteins. In the context of cell differentiation, certain genes are expressed, producing transcription factors that regulate which proteins are synthesized by the cell. These proteins, in turn, signal a cell to differentiate into a specialized cell type with unique morphological and physiological characteristics. Transcription factors are a class of proteins that bind to specific genes on the DNA molecule to promote or inhibit their transcription, thus playing a pivotal role in cellular differentiation.