Final answer:
To track the expression of a protein in live animals during development, the best method is by using a transgenic organism that expresses a GFP fusion protein, enabling visualization of protein production in real-time.
Step-by-step explanation:
The best method to follow the timing of expression of a given protein during development in a live animal is by using a transgenic organism that expresses a GFP fusion protein. This approach is very powerful because it allows the visualization of when and where a protein is expressed in a living organism in real-time. The GFP (Green Fluorescent Protein) gene is used as a reporter gene, and when it is fused to the gene of interest, the resultant protein can be easily tracked due to GFP's fluorescence under ultraviolet light.
Transgenic animals can serve as a model for studying gene expression patterns and the effects of recombinant genes. For instance, mice are commonly used as they can express the fluorescent marker, allowing researchers to monitor the presence and quantity of the target protein in various stages of development.