Question

as a zygote (unborn baby) divides (to form two) to form new cells, groups of cells specialize to carry out functions that are essential (needed) to the organism. what causes cells to differentiate into specialized cells? the activation (to make happen) of specific causes cells to differentiate (to make different things) into specialized cells (cells that do something)

Explanation:

Cell - differentiation is caused by the activation of specific genes. Genes contain the instructions for making proteins, and different combinations of activated genes lead to different cell - types with specialized functions.

Answer:

genes