From a single fertilized ovum undergoing a series of rapid cell divisions, a human infant develops. The embryonic cells become specialized for a variety of functions. Which of these statements best describes how different cell types develop

Each cell type contains only the active parts of the DNA needed for that cell type
Each cell type has only one chromosome containing the DNA needed for that cell type.
Each cell has an identical copy of DNA with enzymes controlling the expression of specific genes, leading to a variety of cells
Each cell has multiple copies of DNA that are affected in different ways by the environment to change the function of the cell at regular intervals.

The correct answer would be that each cell has an identical copy of DNA with enzymes controlling the expression of specific genes, leading to a variety of cells .

Cell differentiation occurs when a specific segment of the DNA of a cell is expressed during gene regulation and control. The segment of DNA expressed would be dependent on the function the cell is meant to perform. Thus, if cell A is meant to perform an excretory role and cell B is meant to perform a digestive role, even though cells A and B contain the same DNA, different segments of their DNAs would be expressed so that each cell becomes adapted to its role.