Complete the accompanying table, indicating whether functionally active -galactosidase and permease are produced in the presence and absence of lactose. Use '+' to indicate the presence of a functional enzyme and '−' to indicate its absence. Indicate whether the partial diploid strain is lac⁺ (able to grow on lactose-only medium) or lac⁻ (cannot grow on lactose medium).

Verified step by step guidance

1. Step 1: Understand the lac operon system, which controls the production of β-galactosidase and permease enzymes. These enzymes are involved in lactose metabolism, where β-galactosidase breaks down lactose and permease facilitates lactose entry into the cell.
2. Step 2: Identify the genetic components involved in the partial diploid strain, including the lacZ gene (encoding β-galactosidase), lacY gene (encoding permease), and the regulatory elements such as the lacI repressor and the operator site. Determine which alleles are present on each chromosome in the diploid.
3. Step 3: Analyze the presence or absence of lactose. In the absence of lactose, the lacI repressor binds to the operator, preventing transcription of lacZ and lacY, so both enzymes are typically not produced (indicated by '−'). In the presence of lactose, the repressor is inactivated, allowing transcription and production of both enzymes (indicated by '+').
4. Step 4: For each genotype in the partial diploid, determine whether functional β-galactosidase and permease are produced in the presence and absence of lactose by considering the effects of mutations or regulatory changes on gene expression.
5. Step 5: Based on the enzyme production patterns, decide if the partial diploid strain is lac⁺ (if it produces functional enzymes and can grow on lactose-only medium) or lac⁻ (if it cannot produce functional enzymes and cannot grow on lactose).

Key Concepts

Lac Operon Structure and Function

The lac operon is a set of genes in E. coli responsible for lactose metabolism, including genes for β-galactosidase and permease. It is regulated by the presence or absence of lactose, which acts as an inducer to enable transcription of these genes. Understanding this operon is essential to predict enzyme production under different conditions.

Role of β-Galactosidase and Permease

β-galactosidase breaks down lactose into glucose and galactose, while permease facilitates lactose entry into the cell. The presence or absence of these functional enzymes determines whether the bacteria can metabolize lactose and grow on lactose-only medium, making their activity critical for lac⁺ or lac⁻ classification.

Partial Diploid Strains and Gene Regulation

Partial diploids carry two copies of the lac operon, allowing analysis of dominant and recessive mutations in regulatory and structural genes. This helps determine how mutations affect enzyme production and lactose metabolism, which is key to interpreting the phenotype (lac⁺ or lac⁻) in the presence or absence of lactose.