Suppose the lac operon partial diploid cap⁻ I⁺ P⁺ O⁺ Z⁻ Y⁺/ cap⁺ I⁻ P⁺ O⁺ Z⁺ Y⁻ is grown.
Is transcription of β-galactosidase and permease inducible, constitutive, or noninducible?

Verified step by step guidance

1. Understand the components of the lac operon: The lac operon is a set of genes involved in lactose metabolism in bacteria. It includes structural genes (Z for β-galactosidase, Y for permease), regulatory elements (I for the repressor, P for the promoter, O for the operator), and CAP (catabolite activator protein) for positive regulation.
2. Analyze the genotype of the partial diploid: The genotype is cap⁻ I⁺ P⁺ O⁺ Z⁻ Y⁺ / cap⁺ I⁻ P⁺ O⁺ Z⁺ Y⁻. This means there are two copies of the operon. The first copy has a defective CAP (cap⁻), a functional repressor (I⁺), a functional promoter (P⁺), a functional operator (O⁺), a defective β-galactosidase gene (Z⁻), and a functional permease gene (Y⁺). The second copy has a functional CAP (cap⁺), a defective repressor (I⁻), a functional promoter (P⁺), a functional operator (O⁺), a functional β-galactosidase gene (Z⁺), and a defective permease gene (Y⁻).
3. Determine the role of CAP: CAP is required for efficient transcription of the lac operon in the presence of lactose and low glucose. Since one copy of the operon has a functional CAP (cap⁺), this copy can respond to glucose levels, while the other copy (cap⁻) cannot.
4. Evaluate the repressor's role: The I⁺ allele produces a functional repressor that can bind to the operator and block transcription in the absence of lactose. The I⁻ allele produces a nonfunctional repressor. Since the functional repressor (I⁺) is trans-dominant, it will regulate both copies of the operon.
5. Assess the transcriptional outcome: In the presence of lactose, the functional repressor (I⁺) will be inactivated, allowing transcription of the operon. The functional CAP (cap⁺) will enhance transcription of the second copy of the operon. Therefore, β-galactosidase (Z⁺) and permease (Y⁺) will be inducible, as their transcription depends on the presence of lactose and low glucose.

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) and regulatory elements (promoter P, operator O, and the repressor gene I). Understanding the operon's structure is crucial for determining how gene expression is regulated in response to lactose availability.

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 describes genes that are continuously active regardless of environmental conditions. Recognizing these terms helps in analyzing how the lac operon responds to different genetic configurations.

Partial Diploidy

Partial diploidy occurs when an organism has two copies of some genes but not others, often due to genetic manipulation. In the context of the lac operon, this can affect the expression of genes like Z and Y, leading to different phenotypic outcomes. Understanding partial diploidy is essential for predicting how mutations and gene interactions influence operon function.