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⁺ O⁺ Z⁺ Y⁻

Verified step by step guidance

1. Identify the components of the lac operon: I (repressor), P (promoter), O (operator), Z (β-galactosidase), and Y (permease).
2. Determine the functionality of each component in the given genotype: I⁺ (functional repressor), P⁺ (functional promoter), O⁺ (functional operator), Z⁺ (functional β-galactosidase), Y⁻ (non-functional permease).
3. Assess the ability of the operon to be inducibly transcribed: Since I⁺ is functional, it can bind to the operator O⁺ and block transcription in the absence of an inducer. In the presence of an inducer, the repressor is inactivated, allowing transcription.
4. Evaluate the ability of the strain to grow on lactose-only medium: Z⁺ allows for the breakdown of lactose, but Y⁻ means lactose cannot be transported into the cell, so the strain is lac⁻.
5. Conclude that the operon is inducibly transcribed due to the presence of a functional repressor and operator, but the strain is lac⁻ because it cannot grow on lactose-only medium due to the non-functional permease.

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 structural genes (Z, Y, and A) that code for proteins necessary for lactose utilization, along with regulatory elements such as the promoter (P) and operator (O). Understanding the operon's structure is crucial for determining how mutations affect gene expression.

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. Identifying whether a genotype leads to inducible or constitutive expression is key to understanding its growth capabilities on lactose.

Haploid Genotypes and Mutations

Haploid genotypes contain a single set of chromosomes, making them particularly useful for studying gene function and expression. Mutations in the lac operon can affect the function of the operon, such as mutations in the operator or structural genes, leading to different phenotypes like lac⁺ (able to utilize lactose) or lac⁻ (unable to utilize lactose). Analyzing these mutations helps predict the operon's behavior under various conditions.