The vertebrate limb bud is an ideal model system forexploring the genetic regulation of development.
(A) In the context of limb development, definethe abbreviation \"ZPA\". What is the major morphogen that issecretes? 2 marks
(B)  (i) What axisis patterned by the ZPA in limb development? Describe ONEexperiment demonstrating the function of theZPA.  4 marks
(ii) In THREE dot points, describe how thismorphogen patterns structures in the autopod. 3marks
C) In FOUR dot points, describe theintracellular signalling pathway that is activated by the main ZPAmorphogen.  4 marks
D) A change in this morphogen underlies limbloss in snakes. At the genetic level, what is this change and whatis the resulting change to the morphogen?  2marks