You are investigating the Bmp4 gene, which is involved in beak development, in the Darwin's finch Geospiza fortis. You find a DNA polymorphism, a single-base difference between two alleles at this locus.

a) Does this polymorphism necessarily have an effect on the phenotypes of the birds of this species? Justify your answer.

b) DNA samples have been saved from the G. fortis that lived on the island of Daphne Major. The samples were taken from birds that lived before and after the severe drought that Peter and Rosemary Grant investigated. How could you see these samples to investigate the relationship between the Bmp4 polymorphism that you have discovered and the phenotypic differences that the Grants saw in the birds before and after the drought? Would your experiment prove that there is (or that there is not) a connection between the polymorphism and the phenotpyic difference? Why?