Sketch a schematic diagram of lac operon in switched on position. How is the operon switched off? Explain.

OR


A tall pea plant bearing violet flowers is given with its unknown genotypes. Explain by working out the crosses how would you find the correct genotypes with respect to the two traits mentioned only by “selfing” the given plants.




Fig.Lac operon in switched on position


• Lac operon of switched on and switched off depends on the presence or absence of lactose.


• When all lactose molecules are digested then repressor protein is free.


• In the operon, the repressor protein binds to the operator region that inhibits the transcription process which results switched off operon.


OR


Let consider,


Tall plant= TT/ Tt


Violet flowers= WW/ Ww


As given, the progeny is a tall pea plant with violet flower.


Let consider the genotype of a given plant could be either of four: TTWW, TTWw, TtWW, TtWw.


Case 1:


Selfing of TTWW:



F1 generation



If all the progeny tall and violet, then genotype of parent is TTWW.


Case 2:


Selfing of TTWw:



F1 generation



If the Phynotype ratio: 3 (tall violet): 1 (tall white) then Parent is TTWw.


Case 3:


Selfing of TtWW:



F1 generation



If phenotypic ratio is 3:1 ,(3 tall violet :1 dwarf violet) then parent will beTtWW.


Case 4:


Selfing of TtWw:



F1 generation



If phenotypic ratio 9:3:3:1, then parent is TtWw.


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