Final answer:
Cell differentiation in mammals is typically considered irreversible as cells become specialized with distinct functions, controlled by gene expression and transcription factors. However, certain stem cells can exhibit some level of reversibility under specific conditions.
Step-by-step explanation:
Cell differentiation in mammals is generally considered to be irreversible. Once cells specialize and assume their unique structures and functions during embryonic development or from stem cells, they typically do not change back to a stem cell state or convert into other cell types under normal conditions.
Cell differentiation is driven by gene expression regulated by transcription factors. These proteins bind to DNA and promote or inhibit the transcription of genes, leading to specialized cell types with unique morphological and physiological characteristics. This process is crucial during development and is a key aspect of the body's ability to maintain different tissues and organs.
However, there are some exceptions to cell differentiation being completely irreversible, such as in the case of certain stem cells that can differentiate into multiple cell types or under experimental conditions in the lab. But for the purpose of this question, and in the general understanding of mammalian development, differentiation is usually irreversible, which would make option 1 (True) the correct answer.