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 In another experiment, the geneticist crossed two purple-eyed, 'rib-it' utterers together with the results shown here: 9/16 purple-eyed, 'rib-it' utterer 3/16 purple-eyed, 'knee-deep' mutterer 3/16 green-eyed, 'rib-it' utterer 1/16 green-eyed, 'knee-deep' mutterer What were the genotypes of the two parents?

Key Concepts

Mendelian Genetics

Mendelian genetics is the study of how traits are inherited through generations based on the principles established by Gregor Mendel. It involves understanding dominant and recessive alleles, genotype versus phenotype, and the segregation and independent assortment of genes during gamete formation. This framework is essential for predicting the outcomes of genetic crosses, such as those described in the frog experiment.

Punnett Squares

Punnett squares are a graphical method used to predict the genotypes and phenotypes of offspring from a genetic cross. By organizing the alleles of the parents, a Punnett square allows for the visualization of all possible combinations in the offspring. This tool is particularly useful in determining the expected ratios of traits, as seen in the F₁ and F₂ generations of the frog experiment.

Phenotypic Ratios

Phenotypic ratios represent the relative frequencies of different observable traits in the offspring resulting from a genetic cross. In the context of the frog experiment, analyzing the phenotypic ratios of the F₂ generation helps to infer the underlying genotypes of the parent frogs. Understanding these ratios is crucial for deducing how traits are expressed and inherited, guiding the geneticist in determining the parental genotypes.