he bodies of wild-type fruit flies are colored by dark pigments, but an X-linked recessive mutation can confer a yellow, unpigmented phenotype. However, feeding silver salts to larvae results in adult flies that phenocopy the yellow phenotype. You are conducting epistasis experiments in fruit flies to understand the genetics of pigmentation. A rival research lab sends you a vial of yellow-bodied flies for your experiments. How can you tell whether these flies are mutants instead of phenocopies

We could feed them with another type of food free of silver salts.

Explanation:

When talking about a phenocopy, we are referring to individuals who genotypically should be expressing a determined phenotype, but due to environmental influence, they express another phenotype. This is a non-inheritable phenotype, so it is not considered a mutation.

If we grow thy flies feeding them another type of food that does not include silver salts, and let them mate and reproduce, they will express the real phenotype, because they will not be influenced by the food. In the following generation, there will be dark individuals carrying the dominant allele, and yellow individuals, with the recessive genotype.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).