Rosemary and peter grant of princeton university have studied finches on the galapagos islands since 1973. they found that when drought conditions on the islands increased, the seeds produced by some of the plants that provided food for the finches were affected. the drought decreased the supply of plants that produced easily cracked seeds, but permitted the survival of plants that produced larger, tougher seeds. only finches with strong, wide beaks could break open the tougher seeds. w

During crossing-over, a. genetic material is exchanged between nonsister chromatids, resulting in new combinations of alleles. b. nonsister chromatids from each homologous chromosome of a tetrad are exchanged, resulting in new combinations of alleles. c. one homologous chromosome of a tetrad is exchanged with another tetrad, resulting in new combinations of alleles. d. sister chromatids from each homologous chromosome of a tetrad are exchanged, resulting in new combinations of alleles. e. genetic material is exchanged between sister chromatids, resulting in new combinations of alleles.