Class 12 Biology - KERALA
Molecular Basis of Inheritance
The chapter Molecular Basis of Inheritance explores DNA as the primary genetic material, detailing its structure discovered by Watson and Crick, replication, and how genetic information flows from DNA to RNA to protein via the Central Dogma. Kerala SCERT Class 12 students will learn about transcription, translation, the genetic code, and the landmark experiments of Griffith, Hershey-Chase, and Meselson-Stahl. It also covers gene regulation through the lac operon and the significance of the Human Genome Project and DNA fingerprinting. This is a high-weightage chapter crucial for scoring top marks in board exams and competitive tests like NEET.
Start Learning FreeKey Concepts
DNA Double Helix
DNA consists of two polynucleotide chains wrapped around each other in a double helix, with sugar-phosphate backbones on the outside and paired nitrogenous bases (A-T, G-C) on the inside linked by hydrogen bonds.
Central Dogma of Molecular Biology
Proposed by Francis Crick, it states that genetic information flows in one direction: from DNA to mRNA via transcription, and from mRNA to proteins via translation.
DNA Replication
The semi-conservative process where DNA makes a copy of itself during the S-phase of the cell cycle, catalyzed by DNA polymerase using each original strand as a template.
Transcription and Genetic Code
Transcription copies genetic info from DNA to mRNA using RNA polymerase. The genetic code is triplet, universal, degenerate, and non-overlapping, translating nucleotide sequences into amino acids.
Lac Operon
An inducible operon in bacteria like E. coli consisting of structural genes (z, y, a), a promoter, an operator, and a regulator gene, responsible for lactose metabolism.
DNA Fingerprinting
A technique developed by Alec Jeffreys that identifies individuals based on variations in repetitive DNA sequences known as Variable Number of Tandem Repeats (VNTRs).
Important Formulas
Board Exam Info
In the Kerala (SCERT) Class 12 Biology board exams, Molecular Basis of Inheritance is a high-scoring chapter that typically carries around 8 to 12 marks. Questions frequently include essay types on DNA replication or transcription, short answers on the Lac operon and Hershey-Chase experiment, and problems based on Chargaff's rule or genetic code.
Frequently Asked Questions
What is the difference between leading and lagging strands during DNA replication?
The leading strand is synthesized continuously in the 5' to 3' direction towards the replication fork, while the lagging strand is synthesized discontinuously in short segments called Okazaki fragments away from the replication fork.
Why is DNA considered a better genetic material than RNA?
DNA is chemically more stable due to the presence of deoxyribose sugar (lacking a 2'-OH group) and thymine instead of uracil, making it less prone to mutations and better suited for storing genetic information safely over generations.
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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