**Core Concept**
Cell fusion is a process used in genetic recombination techniques to merge two cells into a single cell, allowing for the exchange of genetic material. This process can be achieved through various methods, each with its own mechanism of action.

**Why the Correct Answer is Right**
Fusion mediated by altering membrane viscosity is not a recognized method of cell fusion in genetic recombination techniques. Cell fusion typically involves the use of agents that increase the permeability of cell membranes, allowing them to fuse together. Options A, B, and C describe valid methods of cell fusion, whereas option D is incorrect.

**Why Each Wrong Option is Incorrect**
**Option A:** Ethylene glycol is a chemical that can increase the permeability of cell membranes, making it a potential agent for cell fusion. It works by disrupting the lipid bilayer of the cell membrane, allowing the fusion of two cells.
**Option B:** Electric current can be used to fuse cells by applying an electrical pulse that causes the cell membranes to merge. This method is often used in techniques such as electrofusion.
**Option C:** Viral transformation can also be used to fuse cells, as certain viruses can cause cells to fuse together as part of their reproductive cycle.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that cell fusion is a critical step in various genetic recombination techniques, including somatic cell hybridization and cell fusion-mediated gene transfer. Understanding the different methods of cell fusion is crucial for the successful application of these techniques in genetic engineering and research.

**✓ Correct Answer: D. Fusion Mediated by altering membrane viscocity**