ICAR AIEEA PG 2024 - Plant Sciences

विस्तृत व्याख्या:

Tumor-Inducing (Ti) Plasmid (टीआई प्लास्मिड):

• The Ti (Tumor-inducing) plasmid is a large circular extrachromosomal plasmid found in the soil bacterium Agrobacterium tumefaciens.
• It is the etiological determinant of Crown gall disease (क्राउन गॉल रोग), an oncogenic plant disease affecting hundreds of dicotyledonous species.
• During infection, the T-DNA (transferred DNA) region of the Ti plasmid is stably transferred and integrated into the host plant nuclear genome, directing host cells to overproduce phytohormones (auxin and cytokinin) resulting in autonomous crown gall tumor proliferation.

Correct Answer: Option 1 (Crown gall).

विस्तृत व्याख्या:

Restriction Endonucleases and Recognition Sequences (प्रतिबंधन स्थल):

• Restriction endonucleases (molecular scissors) cleave double-stranded DNA at or near specific nucleotide sequences.
• The specific 4 to 8 base-pair DNA sequence recognized and bound by a restriction endonuclease is officially known as the Recognition sequence or Restriction site (पहचान अनुक्रम या प्रतिबंधन स्थल).
• In Type II restriction enzymes (such as EcoRI, recognizing $5'\text{-GAATTC-}3'$), these sites are typically palindromic sequences with two-fold rotational symmetry.

Correct Answer: Option 3 (Recognition sequence or restriction site).

विस्तृत व्याख्या:

Chromosome Condensation in the Cell Cycle (गुणसूत्र संघनन एवं दृश्यता):

• During Interphase ($G_1$, S, and $G_2$ phases), chromosomes exist in a decondensed, diffuse chromatin state to allow active gene transcription and DNA replication, making individual chromosomes indistinguishable under a light microscope.
• During the M phase (Mitosis), condensin complexes and histone phosphorylation drive maximal chromosome supercoiling and condensation.
• At Metaphase of M phase, chromosomes achieve their peak state of structural condensation and are arranged along the equatorial plate, making them most distinct, measurable, and ideal for karyotyping and cytogenetic analysis.

Correct Answer: Option 4 (M phase (mitosis)).