CBSE(NCERT) GRADE 12 BIOTECHNOLOGY 2025 SET1

Sanger’s method of DNA sequencing is a widely used technique to determine the nucleotide sequence of a DNA fragment. Primers are extended using the single strand DNA template as a guide, where the normal substrates i.e. deoxynucleotide 5′ triphosphates (dNTPs) are incorporated in the growing DNA chain. This method is based upon the principle of chain termination by ddNTPs (2′, 3′ dideoxynucleotide tri phosphates) which, if incorporated into each extending chain (instead of the required dNTP) cause termination. Radioactive primers may be used to visualize separated strands in the gel by autoradiography. Nowadays, DNA sequencing have become automated, where ddNTPs are conjugated with fluorescent molecules and the gels obtained are scanned by laser.

Genetically modified or transgenic crops with improved agronomic traits have been developed by introduction of foreign genes into crop plants, using cell and tissue culture systems. The explants are cultured on a suitable nutrient medium which provides macro -nutrients, micronutrients, carbon source, vitamins, amino acids alongwith plant hormones required for growth, cell division and development of plant cells in culture. Plant cell culture and applications deal with various types of cultures such as organ culture, explant culture, callus culture, cell suspension culture, protoplast culture, mass cell culture and each of these have widespread uses in plant regeneration, genetic transformation studies, and many more applications of plant cell and tissue culture.