Answer:
A. an increase in genetic diversity
Step-by-step explanation:
Genetic diversity is the degree of gene variety within a single species (animal or plant). It corresponds to the total number of genetic characteristics in the genetic composition of species or subspecies. Genetic diversity is one of the main aspects of our planet's biodiversity, such as populations and ecosystems.
In the case of Siamese cats, genetic diversity has caused some lineages to change their appearance from classic to modern. This occurred by crossing Siamese cats with cats of other breeds, creating a wide genetic variety that resulted in the change in appearance of these cats.