Which of the following is an example of a genetic alteration?

Transgenic mice are a prime example of a genetic alteration because they have had specific genes from another species inserted into their genome. This manipulation allows researchers to study the effects of these foreign genes on the organism's development, physiology, and behaviors. Transgenic models are vital for understanding gene function and for developing treatments for various diseases, making them a significant tool in genetic research.

In contrast, hybrid vigor refers to an increase in biological fitness resulting from the hybridization of two different strains or breeds, which does not involve a direct alteration of genes. Mutable phenotypes describe variability in traits that can change under different environmental conditions but don't necessarily signify a genetic change at the DNA level. Clonal selection is a process associated with the immune system where specific cells proliferate in response to antigens, again not representing a genetic alteration in the context of manipulating an organism's genome.