A geneticist from an alien planet that prohibits genetic research brought with him to Earth two pure-breeding lines of frogs. One line croaks by uttering 'rib-it rib-it' and has purple eyes. The other line croaks more softly by muttering 'knee-deep knee-deep' and has green eyes. With a newfound freedom of inquiry, the geneticist mated the two types of frogs, producing F₁ frogs that were all utterers and had blue eyes. A large F₂ generation then yielded the following ratios: 27/64 blue-eyed, 'rib-it' utterer 12/64 green-eyed, 'rib-it' utterer 9/64 blue-eyed, 'knee-deep' mutterer 9/64 purple-eyed, 'rib-it' utterer 4/64 green-eyed, 'knee-deep' mutterer 3/64 purple-eyed, 'knee-deep' mutterer One set of crosses with his true-breeding lines initially caused the geneticist some confusion. When he crossed true-breeding purple-eyed, 'knee-deep' mutterers with true-breeding green-eyed, 'knee-deep' mutterers, he often got different results. In some matings, all offspring were blue-eyed, 'knee-deep' mutterers, but in other matings all offspring were purple-eyed, 'knee-deep' mutterers. In still a third mating, 1/2 blue-eyed, 'knee-deep' mutterers and 1/2 purple-eyed, 'knee-deep' mutterers were observed. Explain why the results differed.