Experiments addressing axis patterning in amphibian embryos are listed in Column X and the observations are listed in Column Y.
Column X
A. Grafting of dorsal blastopore lip from donor early gastrula into presumptive ventral epidermis of host early gastrula
B. Injection of noggin mRNA into UV-treated Xenopus embryos
C. Injection of morpholinos to inhibit BMPs 2, 4, and 7
D. Grafting of anterior archenteron roof from late gastrula into the blastocoel of early gastrula
Column Y
i. Rescue of dorsal development
ii. Induction of secondary head structures
iii. Formation of a secondary embryo
iv. Enlarged neural tube
Which one of the following options represents all correct matches between Column X and Column Y?

Correct option is D

Correct Answer:
(d) A–iii, B–ii, C–iv, D–i
Explanation:
The dorsal blastopore lip (Spemann organizer) has organizer activity and induces a secondary embryo when grafted ventrally (A–iii).
Noggin antagonizes BMP signaling and promotes anterior neural fate, leading to secondary head structures even in UV-ventralized embryos (B–ii).
Inhibition of BMPs (2, 4, 7) enhances neural induction, resulting in an enlarged neural tube (C–iv).
The anterior archenteron roof contains organizer-derived signals that can rescue dorsal development when grafted (D–i).
Information Booster :
· Spemann–Mangold experiments established the concept of an organizer.
· BMP inhibition is central to neural induction in amphibian embryos.
· Noggin, Chordin, and Follistatin act as BMP antagonists.
· Organizer activity varies temporally and spatially during gastrulation.
Additional Information (Incorrect Options):
A–ii / A–iv: Dorsal blastopore lip induces a full secondary axis, not just head structures or neural tube enlargement.
B–i / B–iii: Noggin injection primarily induces anterior neural structures, not a complete secondary embryo or simple dorsal rescue alone.
D–ii / D–iii: Anterior archenteron roof lacks strong organizer activity to induce a complete secondary embryo or isolated head structures.