if one can understand a few things it is easier to solve these kind of questions. first comes to I which codes for repressor. there are 3 types - I+ Wild type and is normal and make Z and Y products in the presence of lactose only. I- is a recessive mutation will make products of Z and Y in the presence and the absence of lactose. Is is a dominant mutation will stop both the products Z and Y. if you have atlease one Is in the question neither the products will from no matter whether the lactose is presence or not. then comes to Operator (O) ,O+ is a wild type and can produce both the products of Z and Y. in the presence of lactose.and Oc is the mutation and can produce both Z and Y products in the Presence and even in the absence of lactose. next comes to Z+ represents production of -galactosidase and Z- represents no production of - galactosidase. 1.Ans. I+P-O+Z+Y+ In this haploid genotype the transcription of operon genes totally absent. Transcription of structural genes is not occured. because here P- indicates the mutation in the promoter site, the RNA polymerase unable to bind to the Promoter and initiate transcription of structural genes. so these cells cannot able to grow on media which contain lactose as sole carbon source. the Strain is lac- 2.Ans.I+P+OcZ+Y- here Oc is the mutation and can produce both Z and Y products in the Presence and even in the absence of lactose means constitutively. but here only the product beta galctosidase produced constitutively and the permease is not produced because Permease gene is is mutated (Y-). these cells also cannot able to grow on media which contain lactose as sole carbon source.because the absence of functional permease enzyme so the Strain is lac- 3.Ans. I-P+OcZ+Y+ here I- is a recessive mutation will make products of Z and Y in the presence and the absence of lactose and Oc is the mutation and can produce both Z and Y products in the Presence and even in the absence of lactose. so this haploid genotype transcribes operon genes constitutively. and both the products of Z and Y expressed continuously, so these cells able to grow on the media which contain lactose as sole carbon source. the strain is lac+ b. partially diploid cap-I+P+O+Z-Y+/Cap+I-P+O+Z+Y- these cells can able to grow on lactose medium because these cells have presence of wild promoter which can able to active the transcription of structural genes. so these cells can able to grow on the media which contain lactose as sole carbon source. ii. Transcription of beta-galactosidase and permease is Inducible though diploid cell have mutated inducer region which can able to activate constitutive expression but Wild type (I+) is dominant over I- . so it is inducible operon. Solution if one can understand a few things it is easier to solve these kind of questions. first comes to I which codes for repressor. there are 3 types - I+ Wild type and is normal and make Z and Y products in the presence of lactose only. I- is a recessive mutation .