NCERT Solutions for class 12 Biology Chapter 6
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Solutions for 12 Biology Chapter 6
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Class 12 Biology Chapter 6 Question Answers
Important terms to know
- Genome: Sum total of genes in haploid set of chromosomes.
- Satellite DNA: The repetitive DNA sequences which form a large portion of genome and have high degree of polymorphism but do not code for any proteins.
- DNA Polymorphism: The variations at genetic level, where an inheritable mutation is observed, in a population at high frequency.
- Operon: A group of genes which control a metabolic pathway.
- Introns: The regions of a gene which are removed during the processing of mRNA.
- Exons: The regions of a gene which become part of mRNA and code for different regions of proteins.
- Euchromatin: The region of chromatin which is loosely packed and transcriptionally active, it stains lighter.
- Heterochromatin: The chromatin that is more densely packed, stains dark and is transcriptionally inactive.
- Bioinformatics: Science of use of techniques including statistics, storing as data bases, analysing, modelling and providing access to various aspects of biological information usually on the molecular level.
Splicing: The process in eukaryotic genes in which introns are removed and the exons are joined together to form mRNA.
Double-helix Structure of DNA
It is proposed by Watson and Crick in 1953.
(i) DNA is made up of two polynucleotide chains.
(ii) The backbone is made up of sugar and phosphate and the bases project inside.
(iii) Both polynucleotide chains are antiparallel i.e. on chain has polarity 5`-3` and other chain has 3`-5`.
(iv) These two strands of chains are held together by hydrogen bonds.
(v) Both chains are coiled in right handed fashion. The pitch of helix is 3.4 nm with 10 base pairs in each turn.
Frederick Griffith (1928) performed experiments with Streptococcus phenumoniae and mice. This bacterium has two strains.
1. S-strain (Virulent)-which possess a mucilage coat and has ability to cause pneumonia.
2. R-strain (Nonvirulent) which do not possess mucilage coat and is unable to cause pneumonia.