Suppose the lac operon partial diploid cap⁻ I⁺ P⁺ O⁺ Z⁻ Y⁺/ cap⁺ I⁻ P⁺ O⁺ Z⁺ Y⁻ is grown.
Explain how genetic complementation contributes to the growth habit of this strain.

Verified step by step guidance

1. Understand the genetic makeup of the partial diploid strain. The strain has two copies of the lac operon: one copy is cap⁻ I⁺ P⁺ O⁺ Z⁻ Y⁺, and the other copy is cap⁺ I⁻ P⁺ O⁺ Z⁺ Y⁻. Each component of the operon has a specific role: cap (catabolite activator protein), I (repressor), P (promoter), O (operator), Z (β-galactosidase), and Y (permease).
2. Determine the functionality of each operon copy. The first copy (cap⁻ I⁺ P⁺ O⁺ Z⁻ Y⁺) has a functional repressor (I⁺) and permease (Y⁺), but lacks functional β-galactosidase (Z⁻) and catabolite activator protein (cap⁻). The second copy (cap⁺ I⁻ P⁺ O⁺ Z⁺ Y⁻) has functional β-galactosidase (Z⁺) and catabolite activator protein (cap⁺), but lacks a functional repressor (I⁻) and permease (Y⁻).
3. Apply the concept of genetic complementation. Complementation occurs when two mutations in different genes are compensated for by the presence of functional alleles in the other copy. In this strain, the functional I⁺ from the first copy can regulate both operons, and the functional Z⁺ and cap⁺ from the second copy can contribute to the operon's activity.
4. Analyze the growth habit based on the complementation. The functional I⁺ repressor from the first copy can bind to the operator (O⁺) of both operons, regulating their expression. The functional Z⁺ from the second copy allows for β-galactosidase production, and the functional Y⁺ from the first copy allows for permease production. Together, these proteins enable lactose metabolism under appropriate conditions.
5. Conclude how genetic complementation supports the strain's growth. The combination of functional alleles from both copies of the operon ensures that the strain can metabolize lactose, despite each individual operon copy having deficiencies. This demonstrates the importance of genetic complementation in restoring functionality in partial diploids.

Key Concepts

Lac Operon

The lac operon is a set of genes in E. coli that are involved in the metabolism of lactose. It consists of structural genes (lacZ, lacY, and lacA) and regulatory elements (promoter and operator). The operon is typically off when lactose is absent and activated in its presence, allowing the bacteria to utilize lactose as an energy source. Understanding the lac operon is crucial for analyzing how mutations and genetic complementation affect gene expression and metabolic capabilities.

Genetic Complementation

Genetic complementation occurs when two different genetic mutations in a diploid organism can restore a normal phenotype when present together. In the context of the lac operon, if one allele is non-functional (e.g., Z⁻), but a functional allele is present on the homologous chromosome (e.g., Z⁺), the functional gene can compensate for the defective one. This principle is essential for understanding how different mutations can interact and influence the growth and metabolic functions of bacterial strains.

Partial Diploidy

Partial diploidy refers to a genetic condition where an organism has two copies of some genes but only one copy of others, often due to the introduction of a plasmid or a specific genetic construct. In the case of the lac operon, the presence of both cap⁻ and cap⁺ alleles allows for the study of gene interactions and complementation. This concept is vital for understanding how different alleles can affect the operon's function and the overall growth of the bacterial strain.