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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:
- (a) How many total gene pairs are involved in the inheritance of both traits? Support your answer.
- (b) Of these, how many are controlling eye color? How can you tell? How many are controlling croaking?
- (c) Assign gene symbols for all
phenotypes and indicate the genotypes of the P1 and F1 frogs. - (d) Indicate the genotypes of the six F2 phenotypes.
- (e) After years of experiments, the geneticist isolated pure-breeding strains of all six F2 phenotypes. Indicate the F1 and F2 phenotypic ratios of the following cross using these pure-breeding strains: blue-eyed, “knee-deep” mutterer × purple-eyed, “rib-it” utterer.
- (f) 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.
- (g) In another experiment, the geneticist crossed two purple-eyed, “rib-it” utterers together with the results shown here:
What were the genotypes of the two parents?
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