CORRECT ANSWER: Option 1 different genes function in each type of cell.

Inside each cell are the genes, which give the cell information about how it is supposed to function. Genes are segments of DNA. Genes are turned on or off for cellular differentiation. For example, to produce the highly specialized nerve cells, only a fraction of the genes are expressed (through transcription with the aid of enzymes) to generate the specific structure and function of the cell.

Option 2 is not the best answer. Though it is true that nerve cells are amitotic, meaning they cannot reproduce, and liver cells can reproduce whenever there ii injury; it is not the main reason why the two types of cells are different in structure and function. It still depends on the genes that dictate the characteristics of the cells.

Option 3 is incorrect. The chromosome number is constant in all cells of an organism. For instance, humans have 46 chromosomes (44 are autosomal and the 2 are sex chromosomes)

Option 4 is incorrect. DNA is known as organism's genetic "fingerprint." Therefore, there is the same DNA found in different cells of the body.