Medical Genetics Pedigree A Pedigree B It is much easier to see how genes flow from generation to generation in Pedigree B II-2 and II-3 are brother and sister. They have two common ancestors, i-1 and i-2Medical Genetics It is much easier to see how genes flow from generation to generation in Pedigree B. II-2 and II-3 are brother and sister. They have two common ancestors, I-1 and I-2