Q21 of 42 Page 1

Explain how ‘sticky ends’ are obtained in a DNA segment. Write their importance in DNA technology.

• Restriction enzymes cut the DNA strand a little away from the centre of the palindrome site, between the same two bases on the opposite strands.


• This leaves the single stranded portions at the ends.


• These overhanging stretches are sticky ends.


• Sticky ends help in joining the foreign DNA (using DNA ligase), with the plasmid to form a recombinant.



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State Gause’s ‘Competitive Exclusion Principle’. How have the recent studies modified this principle?

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Explain the phenomenon of evolution by natural selection as supported by the variations observed in white winged and dark winged moth populations in England between 1850 – 1920.

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Explain ‘mutation breeding’ as a method of developing disease resistant crop plants. Give an example of a pulse crop where this technique has helped.

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(a) Work out the crosses so as to obtain the phenotypic ratios given below:

(i) 1 : 2 : 1 (in F2 generation)


(ii) 3 : 1 (in F2 generation)


(iii) 1 : 1 (in F1 generation)


(b) Differentiate between pleiotropy and polygenic inheritance patterns.


OR


(a) Describe the process of amino acylation.


(b) ‘‘Process of transcription and translation are coupled in prokaryotes, but not in eukaryotes.’’ Explain.