Even though both lens cells and liver cells have numerous transcription factors that are present in both cells, the lens cell makes the crystallin protein (not albumin), whereas the liver cell makes albumin

(not crystallin). Which of the following explains this cell specificity?

a) Different specific transcription factors made in each cell

determine which genes are expressed.

b) At fertilization, specific cells are destined for

certain functions.

c) The activators needed for expression of the crystallin gene are

present in all cells.

d) The promoters are different for the different genes.