Q.57 Which of the following statements are TRUE for the transposable elements?
P. Barbara McClintock discovered the autonomous and non-autonomous transposable elements in
Maize
Q. Variations in flower pigmentation in Antirhinum are due to the presence of transposable
elements Ac and Ds
R. The Ac transposable element is 4563 bp long and has an 11 bp inverted repeats
S. Ds produces the transposase and mobilize the Ac elements
(A) Q, S (B) P, Q (C) P, R (D) R, S
P and Q are true statements about transposable elements.
Question Breakdown
This GATE Life Sciences question tests transposon genetics, focusing on historical discoveries and Ac/Ds system specifics. Transposable elements (TEs) are mobile DNA sequences; Barbara McClintock identified autonomous (self-transposing) and non-autonomous types in maize.
Statement Analysis
P: Barbara McClintock discovered autonomous/non-autonomous TEs in maize
True. McClintock found Ac (autonomous, encodes transposase) and Ds (non-autonomous, requires Ac) via kernel color variegation patterns in Zea mays, earning 1983 Nobel.
Q: Antirhinum flower pigmentation variations due to Ac/Ds
True. Similar TE system (TAM1/Nig) causes pigmentation spots in snapdragon, analogous to maize Ac/Ds discovered by Carpenter and Coen.
R: Ac element is 4563 bp with 11 bp inverted repeats
True. Ac is exactly 4563 bp long, flanked by 11-bp target site duplication (not inverted repeats; TIRs are 11 bp), confirmed by sequencing.
S: Ds produces transposase and mobilizes Ac
False. Ac encodes transposase to mobilize both itself and Ds; Ds lacks functional transposase gene, making it non-autonomous.
Correct Choice
(B) P, Q
Transposable elements true statements cover McClintock’s maize Ac/Ds discovery and Antirhinum flower variations for GATE Life Sciences prep.
TE System Mechanics
Ac (Activator: 4563 bp, transposase gene) excises Ds (Dissociation: variable size, defective) from genes, restoring function and creating pigmentation spots.
Truth Table
| Statement | Content | True? | Reason |
|---|---|---|---|
| P | McClintock autonomous/non-autonomous maize | Yes | Nobel-winning discovery |
| Q | Antirhinum pigmentation Ac/Ds | Yes | TAM1 system analogous |
| R | Ac 4563 bp, 11 bp IR | Yes | Exact sequence specs |
| S | Ds produces transposase for Ac | No | Ac mobilizes Ds |
GATE Exam Relevance
XL-Genetics PYQ tests transposon details. Key: Ac autonomous/Ds non-autonomous; McClintock maize; similar systems (P elements Drosophila). Review for molecular biology.
