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CBSE Class 12th Biology Notes for Chapter 6 Molecular Basis Of Inheritance

​  Chapter 6 Molecular Basis Of Inheritance

  • Nucleic acids are long polymers of nucleotides. While DNA stores genetic information, RNA mostly helps in transfer and expression of information. Though DNA and RNA both function as genetic material but DNA being chemically and structurally more stable is a better genetic material. However, RNA is the first to evolve and DNA was derived from RNA.


  • The hallmark of the double stranded helical structure of DNA is the hydrogen bonding between the bases from opposite strands. The rule is that Adenine pairs with Thymine through two H-bonds and Guanine with Cytosine through three H-bonds. This makes one strand complementary to the other. The DNA replicates semiconservatively, the process guided by the complementary H-bonding. A segment of DNA that codes for RNA may in a simplistic term can be referred as gene. During transcription also, one of the strands of DNA acts as a template to direct the synthesis of complementary RNA. In bacteria, the transcribed mRNA is functional, hence can be directly translated. In eukaryotes, the gene is split.


  • The coding sequences, exons, are interrupted by non-coding sequences, introns. Introns are removed and exons are joined to produce functional RNA by splicing. The messenger RNA contains the base sequences that are read in a combination of three (to make triplet genetic code) to code for an amino acid. The genetic code is read again on the principle of complementary tRNA that acts as an adapter molecule. There are specific tRNAs for every amino acid. The tRNA binds to specific amino acid at one end and pairs through H-bonding with codes on mRNA through its anticodons. The site of translation (protein synthesis) is ribosomes, which bind to mRNA and provide platform for joining of amino acids.


  • DNA fingerprinting is a technique to find out variations in individuals of a population at DNA level. It works on the principle of polymorphism on DNA sequences. It has immense applications in the field of forensic science, genetic biodiversity and evolutionary biology.


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