Class 12 Biology - TAMILNADU
Molecular Basis of Inheritance
The chapter Molecular Basis of Inheritance in Class 12 Biology explores the genetic material of living organisms, focusing primarily on DNA and RNA. Students learn about the search for genetic material, DNA replication, transcription, genetic code, translation, and gene expression regulation via the lac operon. The Human Genome Project and DNA fingerprinting are also covered in detail. This chapter is exceptionally high-scoring and vital for both the Tamil Nadu Samacheer Kalvi board exams and competitive medical entrance tests like NEET, as it explains the biochemical foundations of heredity and molecular genetics.
Start Learning FreeKey Concepts
DNA Structure and Replication
DNA is a double helix made of nucleotides where strands are anti-parallel and complementary. Replication is semi-conservative, meaning each new DNA molecule keeps one original strand and one newly synthesized strand.
Central Dogma of Molecular Biology
Genetic information flows in a unidirectional path: DNA undergoes transcription to form mRNA, which then undergoes translation to synthesize proteins.
Transcription and Genetic Code
Transcription copies genetic info from DNA to mRNA using RNA polymerase. The genetic code consists of 64 triplet codons that dictate amino acid sequences during protein synthesis.
Lac Operon
An inducible operon system in E. coli consisting of structural genes regulated by a common promoter and repressor, demonstrating gene regulation in prokaryotes.
DNA Fingerprinting
A technique developed by Alec Jeffreys that identifies individuals based on variations in their DNA sequences, particularly repetitive DNA known as Variable Number of Tandem Repeats (VNTRs).
Important Formulas
Board Exam Info
In the Tamil Nadu (Samacheer Kalvi) Class 12 Biology board exam, this chapter carries significant weightage, typically ranging from 8 to 12 marks. Questions commonly include descriptive 5-mark answers (such as DNA replication, Lac operon, or Hershey-Chase experiment), 3-mark conceptual questions (like differences between DNA and RNA, features of the genetic code), and multiple-choice questions.
Frequently Asked Questions
What is the difference between leading strand and lagging strand in 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 in the opposite direction.
Why is DNA considered a better genetic material than RNA?
DNA is more chemically stable due to the presence of deoxyribose sugar (lacking the 2'-OH group found in RNA) and is less prone to mutations. It also has a double-stranded nature and repair mechanisms that protect genetic information.
What are the salient features of the genetic code?
The genetic code is triplet, universal, degenerate (multiple codons for one amino acid), unambiguous (one codon specifies only one amino acid), non-overlapping, and has start (AUG) and stop (UAA, UAG, UGA) codons.
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