Q.66 In 1976, Tonegawa’s experiment gave clue about gene rearrangement during differentiation of B-
cells. The two different types of cells used in this experiment were
(A) HeLa cells and fibrosarcoma cells
(B) embryonic cells and fibroblasts
(C) adult myeloma cells and HeLa cells
(D) embryonic cells and adult myeloma cells
Tonegawa’s 1976 experiment used embryonic cells and adult myeloma cells to demonstrate immunoglobulin gene rearrangement in B-cell differentiation.
The correct answer is (D).
Experiment Details
Susumu Tonegawa compared DNA from embryonic mouse cells (germline configuration, no rearrangement) with adult myeloma cells (mature B-lineage tumor cells with rearranged V(C)J genes). Restriction enzyme digestion and hybridization revealed that Ig genes are separate in embryos but joined in myeloma cells, proving somatic recombination during B-cell maturation.
Option Breakdown
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(A) HeLa cells and fibrosarcoma cells: Wrong—HeLa (human cervical cancer, epithelial) and fibrosarcoma (connective tissue sarcoma) bear no relation to B-cell Ig genes or immunology.
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(B) Embryonic cells and fibroblasts: Partially correct but incomplete—fibroblasts (non-lymphoid) don’t undergo Ig rearrangement, unlike myeloma B cells.
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C) Adult myeloma cells and HeLa cells: Wrong—HeLa irrelevant; experiment contrasted developmental stages (embryo vs. mature B).
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(D) Embryonic cells and adult myeloma cells: Correct—Direct germline (embryo) vs. rearranged (myeloma) comparison proved the mechanism.
Introduction to Tonegawa Experiment Gene Rearrangement B-Cells
Tonegawa experiment gene rearrangement b-cells (1976) revolutionized immunology, showing Ig genes somatically recombine during B-lymphocyte differentiation—Nobel-winning discovery for GATE Life Sciences. Embryonic cells (germline) vs. adult myeloma cells (rearranged) provided key evidence via DNA hybridization.
Experimental Design
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Embryonic cells: Unrearranged V, D, J, C segments distant.
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Adult myeloma cells: V(D)J joined to C, forming complete Ig genes.
Restriction mapping confirmed somatic rearrangement, enabling antibody diversity.
Why Other Options Fail
| Option | Issue |
|---|---|
| (A) HeLa + fibrosarcoma | Non-B cell lines, no Ig genes. |
| (B) Embryo + fibroblasts | Fibroblasts lack rearrangement. |
| (C) Myeloma + HeLa | HeLa irrelevant control. |
| (D) Embryo + myeloma | Perfect developmental contrast. |
GATE Relevance
Tonegawa experiment gene rearrangement b-cells tests immunology milestones. Memorize: embryo (germline) vs. myeloma (rearranged) = (D). Essential for XL biochemistry/immunology sections.
