Question

part A: The convergent extension of the ectoderm in Xenopus to form the yolk plug and formation of the embryonic shield in Zebrafish around the yolk use which of the following modes of gastrulation?

Invagination

Involution

Ingression

Delamination

Epiboly

Part B: Which of the following uses Shh as the main paracrine factor to determine anterior posterior digit patterning in the limb?

Node

ZPA

Nieuwkoop center

AER

Organizer