Question

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A partial diploid of genotype it pt ot ztrpt of zº will show: A. Inducible production of B-galactosidase. OB. no production of B-galactosidase. OC. constitutive production of lactose. D. constitutive expression of B-galactosidase. O E. inducible production of repressor.

Answer 1

Correct option: Inducible production of beta-galactosidase

Explanation:

The genes used here are responsible for producing effects as tabulated:

Working gene	Function	Mutated Form	Expected effect of mutated form
I+	Produces a repressor molecule that in absence of lactose inhibits RNA polymerase progression and hence protein/operon expression	I-	No repressor is made, operon remain active no matter lactose is present or not
P+	This is the promoter sequence for the operon. It is necessary for RNA polymerase binding.	P-	No promoter means there will be no site for RNA polymerase to bind. Consequently transcription of a DNA strand lacking this element is not possible.
O+	The operator is a sequence upstream to the structural genes that provide binding site for active repressor binding	O-	No operator means that the repressor will not be able to work on that particular strand. Hence transcription will be always active from that strand
Z+	This is a structural gene of lac operon responsible for encoding the beta-galactosidase enzyme	Z-	Beta-galactosidase will not be produced even if other genes are correctly arranged

The diploid has two DNA strands, one with genotype I+P+O+Z+ and the other with I-P+O+Z-. So, the first strand is normal and hence beta-galctosidase will be produced in presence of lactose, and the beta-galactosidase will not be produced in absence of lactose. This type of regulated expression of beta-galactosidase is called inducible expression of beta galactosidase. The seonfd strand having I-P+O+Z- genotype will not be able to produce beta galactosidase because the beta-galacrosidase gene Z is absent. This means that the beta-galactosidae production is entirely dependent on the first strand. SInce the first strand show inducible production of beta-galactosidase, the overall responsonse will be the same.