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⁺

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), a promoter (P), and an operator (O). The operon is regulated by the presence or absence of lactose, which influences whether the genes are transcribed. Understanding the structure is essential 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 crucial for predicting the growth capabilities of the strain on lactose.

Genotype and Phenotype Relationship

The genotype refers to the genetic constitution of an organism, while the phenotype is the observable characteristics resulting from the genotype and its interaction with the environment. In the context of the lac operon, specific mutations in the genotype (like I⁺, Oᶜ, Z⁻) will determine whether the organism can utilize lactose (lac⁺) or not (lac⁻). Understanding this relationship is key to interpreting the results of the given genotypes.