Q.97 In a newly discovered organism, normal development was unaffected when a few blastomeres were removed
from 100-cell stage embryo. However, removal of five cells at the 1000-cell stage abolished the formation of kidney.
Which one of the following options most accurately describes the type(s) of specification operating in the development of this organism?
(A) Conditional specification only
(B) Autonomous specification only
(C) Conditional and autonomous specifications
(D) Specification does not occur in this organism
Blastomere removal 100-cell vs 1000-cell stage kidney development specification
In this developmental biology experiment, normal development after 100-cell blastomere removal indicates conditional specification (regulative), while kidney failure after 1000-cell removal indicates autonomous specification for kidney lineage. The correct answer is (C) Conditional and autonomous specifications.
Correct Answer
(C) Conditional and autonomous specifications
Both mechanisms operate at different stages in this organism’s development.
Detailed Explanation
Experimental Observations Analysis
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100-cell stage: Removing “a few blastomeres” → normal development unaffected
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Indicates conditional specification (regulative development)
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Remaining cells compensate via cell-cell interactions
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Early embryo totipotent/pluripotent, can regulate
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1000-cell stage: Removing “five cells” → kidney formation abolished
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Indicates autonomous specification (mosaic development)
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Kidney precursor cells removed, no compensation possible
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Late-stage cells lineage-restricted by cytoplasmic determinants
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Specification Types Breakdown
| Stage | Observation | Specification Type | Mechanism |
|---|---|---|---|
| 100-cell | Normal development | Conditional | Cell interactions regulate |
| 1000-cell | No kidney | Autonomous | Fixed lineage, no regulation |
Option Analysis
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(A) Conditional only: Wrong—1000-cell stage shows autonomous (no regulation)
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(B) Autonomous only: Wrong—100-cell stage shows conditional (full regulation)
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(C) Both: ✅ Correct—early conditional, late autonomous specification
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(D) No specification: Wrong—both mechanisms clearly demonstrated
Introduction to Embryonic Specification Cell Removal Experiments
Blastomere removal experiments at 100-cell vs 1000-cell stages test conditional vs autonomous specification in embryonic development. Early regulative capacity (conditional) gives way to lineage restriction (autonomous), crucial for CSIR NET, GATE biotech developmental biology.
Why Both Specification Types Operate
Early (100-cell): Pluripotent blastomeres → conditional specification via inductive signals. Remaining cells reorganize positional values.
Late (1000-cell): Kidney progenitors autonomously specified by cytoplasmic determinants. Removal = permanent lineage loss (mosaic development).
Exam Strategy for Developmental Biology MCQs
Classic pattern: Early embryo = regulative/conditional, late gastrulation = mosaic/autonomous. Remember vertebrate early regulative → invertebrate mosaic transitions.
