Suppose the lac operon partial diploid cap⁻ I⁺ P⁺ O⁺ Z⁻ Y⁺/ cap⁺ I⁻ P⁺ O⁺ Z⁺ Y⁻ is grown.
Will this partial diploid strain grow on a lactose medium?

Verified step by step guidance

1. Step 1: Understand the components of the lac operon. The lac operon is a set of genes in bacteria that are involved in lactose metabolism. It includes the structural genes Z (β-galactosidase) and Y (permease), the promoter (P), the operator (O), the repressor gene (I), and the CAP site (catabolite activator protein binding site).
2. Step 2: Analyze the genotype of the partial diploid strain. The strain is cap⁻ I⁺ P⁺ O⁺ Z⁻ Y⁺ / cap⁺ I⁻ P⁺ O⁺ Z⁺ Y⁻. This means there are two copies of the lac operon: one with a defective CAP site (cap⁻) but functional I, P, O, and Y genes, and a second with a functional CAP site (cap⁺) but defective I and Y genes.
3. Step 3: Determine the functionality of the repressor (I) gene. The I⁺ allele on the first operon produces a functional repressor protein, which can regulate both operons in trans. The I⁻ allele on the second operon is nonfunctional, but this does not matter because the I⁺ allele is dominant.
4. Step 4: Evaluate the structural genes Z and Y. The Z⁻ allele on the first operon means β-galactosidase cannot be produced from that operon, but the Z⁺ allele on the second operon allows β-galactosidase production. Similarly, the Y⁺ allele on the first operon allows permease production, while the Y⁻ allele on the second operon does not. Both enzymes are required for lactose metabolism.
5. Step 5: Assess the impact of the CAP site. The cap⁻ mutation on the first operon means it cannot respond to catabolite repression, but the cap⁺ allele on the second operon allows proper regulation. Since both β-galactosidase and permease can be produced from the two operons, and the CAP site on the second operon is functional, the strain will grow on a lactose medium.

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 encode proteins necessary for lactose uptake and breakdown, along with regulatory elements such as the promoter (P) and operator (O). Understanding the arrangement and function of these components is crucial for predicting the operon's behavior in the presence of lactose.

Partial Diploidy

Partial diploidy refers to a genetic condition where an organism has two copies of some genes but not others, often due to the presence of a plasmid or a chromosomal segment. In the context of the lac operon, this means that the strain has two different alleles for some genes, which can affect the expression of the operon and its ability to metabolize lactose.

Lactose Utilization

For a bacterial strain to grow on lactose medium, it must be able to transport lactose into the cell and metabolize it. This process is facilitated by the proteins encoded by the lac operon. The presence of functional genes (like Z and Y) is essential for lactose utilization, and mutations or deletions in these genes can prevent growth on lactose, making it important to analyze the specific alleles present in the given strain.