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⁺

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, A) that code for proteins necessary for lactose utilization, a promoter (P) where RNA polymerase binds to initiate transcription, and an operator (O) that regulates access to the promoter. Understanding the arrangement and function of these components is crucial for analyzing how different genotypes 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, while constitutive expression refers to genes that are continuously expressed regardless of environmental conditions. In the context of the lac operon, certain mutations can lead to either inducible or constitutive expression of the operon genes, impacting the organism's ability to utilize lactose as a carbon source.

Haploid Genotypes and Phenotypes

Haploid genotypes consist of a single set of chromosomes, which means that any mutation will directly affect the phenotype. In the case of the lac operon, the presence of specific mutations in the operon can determine whether the strain is lac⁺ (able to grow on lactose) or lac⁻ (unable to grow on lactose). Analyzing these genotypes helps predict the growth capabilities of the bacteria on lactose-only media.