94. Which one of the following is consistent with the germplasm theory of August Weismann?
(A) Regulative development observed in frog embryos
(B) Mosaic development observed in tunicates
(C) Normal embryonic development of embryos formed by somatic nuclear transfer
(D) Ability of differentiated cells to form pluripotent stem cells under certain conditions

August Weismann’s germplasm theory emphasizes a strict separation between germ cells (carrying heritable material) and somatic cells, with heredity flowing only from germplasm to somatoplasm via the Weismann barrier. This MCQ tests understanding of that doctrine against developmental biology concepts. The correct answer is (B) Mosaic development observed in tunicates.​

Core Theory Overview

Weismann proposed that germplasm in germ cells holds complete hereditary determinants, which are partitioned during development into somatic cells containing only partial somatoplasm. Changes in somatic cells cannot reverse to affect germplasm, ensuring germline continuity across generations. This aligns with observations where early determinants rigidly dictate cell fates without regulative flexibility.​

Option Analysis

• (A) Regulative development observed in frog embryos: In regulative embryos like frogs, cells adjust fates based on interactions, compensating for lost blastomeres to form complete organisms. This implies potential equivalence of early cells, contradicting Weismann’s idea of irreversible determinant partitioning.​

• (B) Mosaic development observed in tunicates: Tunicate embryos show mosaic development, where each blastomere receives fixed determinants from the zygote, leading to rigid fates—if one cell is removed, the embryo lacks that structure. This matches Weismann’s model of germplasm dividing unequally into specialized somatic lines.​

• (C) Normal embryonic development of embryos formed by somatic nuclear transfer: Somatic nuclear transfer (e.g., cloning) reprograms differentiated somatic nuclei to totipotency, producing viable embryos. This demonstrates somatic material influencing germline potential, violating the Weismann barrier.​

• (D) Ability of differentiated cells to form pluripotent stem cells under certain conditions: Induced pluripotency (e.g., iPS cells) shows somatic cells regaining broad potential, reversing differentiation. This challenges the theory’s claim that somatoplasm cannot regenerate full germplasm.​​