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?
a) To begin with you must determine the consequence of this single base polymorphism. First determine where this polymorphism is occuring. A gene is made up of a promoter region, 5' and 3' untranslated regions, introns and exons. Bases within the promoter region may affect location, timing and amount (any regulatory aspects). Polymorphisms within intronic sequences may also have an impact on regulatory features of the gene expression as enhancer can be found within intron. It would be rare for the single-base polymorphism to affect splice junctions but possible. If the polymorphism is found within the open reading frame or exonic sequence (this is the sequence that directly codes for the amoni acid sequence) it may change the amino acid sequence with the possibility of having a great impact on protein ...
Examination of the effects of polymorphisms on bird speciation with web links.