How are the structural genes activated in the lac operon in E

Subject

Biology

Class

CBSE Class 12

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 Multiple Choice QuestionsShort Answer Type

21. How does industrial melanism support Darwin’s theory of Natural Selection? Explain.
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22. List the salient features of double helix structure of DNA. 
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23. How are the structural genes activated in the lac operon in E.coli


The Lac operon in E.coli  consists of  one regulatory gene (the i gene ) and three structural genes (z, y, and a).Lactose acts as the inducer and it regulates switching on and off of the operon. The i gene produces repressor all-the-time (constitutively) which inactivates the structural gene.The repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon. Lactose inactivates the repressor allowing the  RNA polymerase access to the promoter and transcription proceeds. The structural genes are activated and transcribed.
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24. Trace the life-cycle of malarial parasite in the human body when bitten by an infected female Anopheles. 
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25.

(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.
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26.

(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

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27.

(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. 
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28. How is the amplification of a gene sample of interest carried out using Polymerase Chain Reaction (PCR)? 
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29.

(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. 
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 Multiple Choice QuestionsLong Answer Type

30.

(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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