Class 12 Biology - ISC
Molecular Basis of Inheritance
The chapter Molecular Basis of Inheritance explores DNA and RNA as the genetic materials that control heredity and protein synthesis. ISC Class 12 students will study the structure of DNA, replication, transcription, translation, gene regulation via the Lac operon, and the landmark Human Genome Project. This is a high-weightage chapter in the ISC Biology board exams, frequently featuring direct diagram-based questions on DNA replication forks, transcription units, and numerical problems based on Chargaff's rules and genetic code calculations. Mastering this chapter is essential for scoring well in genetics.
Start Learning FreeKey Concepts
Structure of DNA
DNA is a double helix made of antiparallel polynucleotide strands held together by hydrogen bonds between complementary nitrogenous bases (A-T and G-C).
DNA Replication
The semi-conservative process where DNA makes exact copies of itself using enzymes like DNA polymerase, proceeding continuously on the leading strand and discontinuously on the lagging strand.
Transcription
The synthesis of a single-stranded mRNA molecule from a DNA template strand, catalyzed by RNA polymerase in the nucleus.
Genetic Code
The sequence of nitrogenous bases in mRNA that specifies the amino acid sequence in proteins, characterized by being triplet, universal, degenerate, and non-overlapping.
Lac Operon
An inducible gene regulation system in bacteria consisting of structural genes, a promoter, an operator, and a regulator gene that controls lactose metabolism.
Important Formulas
Board Exam Info
In the ISC Class 12 Biology examination, this chapter typically carries around 8 to 12 marks. Common question types include structural diagrams of the DNA double helix or transcription unit, differences between DNA and RNA or replication and transcription, numerical problems on base ratios, and explanatory questions on the Lac operon and Hershey-Chase experiment.
Frequently Asked Questions
Why is DNA replication considered semi-conservative?
It is semi-conservative because each newly formed DNA molecule consists of one original parent strand and one newly synthesized daughter strand.
What is the role of tRNA during translation?
tRNA acts as an adapter molecule that reads the codon on mRNA through its anticodon loop and brings the specific corresponding amino acid to the ribosome.
How does the Lac operon switch off in the absence of lactose?
In the absence of lactose, the regulator gene produces a repressor protein that binds tightly to the operator region, blocking RNA polymerase from transcribing the structural genes.
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