Correct option is B
Explanation-
Option a : Negative selection markers need to be expressed only under strong constitutive promoters for development of transgenic plants. - INCORRECT
Negative selection markers are genes that kill or inhibit the growth of cells that express them under certain conditions (e.g., cytotoxins or sensitivity to specific chemicals). They do not require strong constitutive (always active) promoters, because their goal is to eliminate cells, not maintain constant expression. In fact, tight regulation is preferred for negative selection to avoid accidental killing of desired cells.
Option b : A transgenic plant containing two linked copies of the transgene in heterozygous condition would segregate in a 3:1 (transgenic : non-transgenic) ratio on self-pollination. - CORRECT
Assume the plant has two identical linked copies of the same transgene inserted at one locus and is heterozygous for that locus (Tt). On self-pollination, a monohybrid cross occurs: Tt × Tt.
According to Mendelian inheritance, the genotypic ratio is:
TT : Tt : tt = 1 : 2 : 1
So, phenotypic ratio (transgenic:non-transgenic) = 3 (TT + Tt) : 1 (tt)
Option c : Agrobacterium-mediated transfer of T-DNA into a host plant does not require host plant proteins. - INCORRECT
Agrobacterium tumefaciens uses host plant proteins to facilitate nuclear import of T-DNA and help in integration into the plant genome. Host proteins like VIP1, importin alpha, and histones interact with the T-DNA complex.
Option d : In a binary vector system of Agrobacterium tumefaciens, the oncogenes are located on the Helper plasmid. - INCORRECT
In the binary vector system, the T-DNA region (with gene of interest) is on a small plasmid (binary vector), and the virulence (vir) genes required for transfer are on a Helper plasmid. The oncogenes (tumor-inducing genes) are removed in genetic engineering to avoid tumor formation. Thus, the Helper plasmid contains vir genes, not oncogenes.
Final Answer: Option b is Correct
