What changes in the central region of the dorsal surface of the single-celled epithelial layer of a… Show more What changes in the central region of the dorsal surface of the single-celled epithelial layer of a chick embryo lead to the formation of the primitive nervous system? 1) a stoppage in the expression of E-cadherin genes 2) a stoppage in the expression of N-cadherin genes 3) an elevation in the expression of N-cadherin genes a)1 b)2 c)3 d)1 and 3 e)1 and 2 • Show less