Short Answer TypeWatson and Crick proposed the double helix for structure of DNA. Its features are:
(i) It is made of two polynucleotide chains, where the sugar-phosphate constitutes the backbone, and the bases project inside.
(ii) The two chains have anti-parallel polarity. It means, if one chain has the polarity 5'-3', the other has 3'-5'.
(iii) The bases in two strands are paired through hydrogen bond (H-bonds) forming base pairs (bp). Adenine forms two hydrogen bonds with Thymine from opposite strand and vice-versa. Similarly, Guanine is bonded with Cytosine with three H-bonds. As a result, always a purine comes opposite to a pyrimidine. This generates approximately uniform distance between the two strands of the helix.
(iv) The two chains are coiled in a right-handed fashion. The pitch of the helix is 3.4 nm (a nanometre is one billionth of a metre, that is 10-9 m) and there are roughly 10 bp in each turn turn. Consequently, the distance between a bp in a helix is approximately equal to 0.34 nm.
(v) The plane of one base pair stacks over the other in double helix.(a) Tobacco plants are damaged severely when infested with Meloidegyne incognitia. Name and explain the strategy that is adopted to stop this infestation.
(b) Name the vector used for introducing the nematode specific gene in tobacco plant.(a) Explain the phenomena of multiple allelism and co-dominanace taking ABO blood group as an example.
(b) What is the phenotype of the following:(i) IAi
(ii) i i
(a) List any three ways of measuring population density of a habitat.
(b) Mention the essential information that can be obtained by studying the population of an organism.(a) What is the programme called that is involved in improving success rate of production of desired hybrid and herd size of cattle?
(b) Explain the method used for carrying this programme for cows.
Long Answer Type(a) Explain the significance of ecological pyramids with the help of an example.
(b) Why are the pyramids referred to as upright or inverted?
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