Correct option is C
The correct answer is (c).
Non-conditional, negative selection marker genes cannot be expressed under a constitutive promoter for the selection of transgenic plants. Non-conditional, negative selection markers require a specific environmental or chemical condition for their expression to function properly. Constitutive promoters, on the other hand, are active continuously and do not allow for such conditions to be created, thus hindering the use of negative selection markers under such promoters.
Incorrect options -
(a)is incorrect because ALS (acetolactate synthase) gene confers resistance to herbicides like sulfonylurea, not antibiotics such as ampicillin. Antibiotic resistance markers like nptII (kanamycin resistance) or bla (ampicillin resistance) are different genes.
(b) is incorrect because Segregation ratios depend on gene linkage: tightly linked genes tend to segregate together, not producing a 15:1 ratio, which is typical of two independent dominant genes.
(d) is incorrect because Multiple T-DNA copies often cause transgene silencing due to methylation and rearrangement, reducing their reliability in long-term studies.
