Identify which of the following lac operon haploid genotypes transcribe operon genes inducibly and which transcribe genes constitutively. Indicate whether the strain is lac⁺ (able to grow on lactose-only medium) or lac⁻ (cannot grow on lactose medium).
I⁺ P⁺ Oᶜ Z⁻ Y⁺

Verified step by step guidance

1. Understand the components of the lac operon: The lac operon consists of the regulatory gene (I), the promoter (P), the operator (O), and the structural genes (Z and Y). The I gene encodes the repressor protein, the O region is the operator where the repressor binds, and Z and Y encode β-galactosidase and permease, respectively.
2. Analyze the given genotype: I⁺ P⁺ Oᶜ Z⁻ Y⁺. Here, I⁺ indicates a functional repressor protein, P⁺ indicates a functional promoter, Oᶜ indicates a constitutive operator mutation (the repressor cannot bind), Z⁻ indicates a nonfunctional β-galactosidase gene, and Y⁺ indicates a functional permease gene.
3. Determine the effect of the Oᶜ mutation: The Oᶜ mutation causes constitutive expression of the operon because the repressor protein cannot bind to the operator. This means that the operon genes downstream of the operator will be transcribed regardless of the presence or absence of lactose.
4. Evaluate the functionality of the structural genes: Since Z⁻ is nonfunctional, β-galactosidase cannot be produced. However, Y⁺ is functional, so permease can be produced. The strain will not be able to metabolize lactose because β-galactosidase is required to break down lactose into glucose and galactose.
5. Conclude the phenotype: The strain transcribes operon genes constitutively due to the Oᶜ mutation. However, it is lac⁻ because it cannot grow on lactose-only medium due to the nonfunctional Z⁻ gene.

Key Concepts

Lac Operon Structure

The lac operon is a set of genes in E. coli that are involved in the metabolism of lactose. It consists of three structural genes (Z, Y, and A) and regulatory elements including the promoter (P) and operator (O). Understanding the operon's structure is crucial for determining how mutations in these components affect gene expression and lactose utilization.

Inducible vs. Constitutive Expression

Inducible expression refers to genes that are turned on in response to specific signals, such as the presence of lactose in the case of the lac operon. In contrast, constitutive expression occurs when genes are continuously expressed regardless of environmental conditions. Recognizing these patterns is essential for analyzing how different genotypes respond to lactose.

Genotype Interpretation

Genotype interpretation involves understanding the specific alleles present in an organism and how they influence phenotype. In the given genotype I⁺ P⁺ Oᶜ Z⁻ Y⁺, the presence of mutations like Oᶜ (operator constitutive) indicates that the operon will be expressed continuously, while Z⁻ suggests a lack of functional β-galactosidase. This knowledge is key to determining whether the strain can grow on lactose.