Datura stramonium (the Jimsonweed) expresses flower colors of purple and white and pod textures of smooth and spiny. The results of two crosses in which the parents were not necessarily true breeding are shown below. Assuming that true-breeding strains of all combinations of traits are available, what single cross could you execute and carry to an F₂ generation that will prove or disprove your hypothesis? Assuming your hypothesis is correct, what results of this cross will support it?

Verified step by step guidance

1. Step 1: Formulate a hypothesis about the inheritance pattern of flower color and pod texture in Datura stramonium. For example, hypothesize that flower color and pod texture are controlled by two independently assorting genes, each with two alleles (dominant and recessive).
2. Step 2: Design a single cross using true-breeding strains for all combinations of traits. For instance, cross a true-breeding purple flower with smooth pod (PPSS) with a true-breeding white flower with spiny pod (ppss). This will ensure that the F1 generation is heterozygous for both traits (PpSs).
3. Step 3: Allow the F1 generation (PpSs) to self-pollinate to produce the F2 generation. This will result in a dihybrid cross, which can be analyzed for phenotypic ratios.
4. Step 4: Predict the expected phenotypic ratios in the F2 generation based on your hypothesis. If the traits are independently assorting, the expected phenotypic ratio will be 9:3:3:1 (9 purple smooth, 3 purple spiny, 3 white smooth, 1 white spiny).
5. Step 5: Compare the observed phenotypic ratios in the F2 generation to the expected ratios. If the observed ratios match the expected 9:3:3:1 ratio, your hypothesis is supported. If not, consider alternative inheritance patterns, such as linkage or epistasis.

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 how these factors influence the inheritance patterns observed in offspring. Mendel's laws, including the Law of Segregation and the Law of Independent Assortment, are foundational for predicting genetic outcomes in crosses.

Punnett Square

A Punnett square is a diagram used to predict the genotypes and phenotypes of offspring from a genetic cross. It organizes the possible combinations of alleles from each parent, allowing for a visual representation of genetic probabilities. By filling in the square with the alleles contributed by each parent, one can easily determine the expected ratios of different traits in the offspring, which is crucial for testing hypotheses about inheritance.

Phenotypic Ratios

Phenotypic ratios refer to the relative frequencies of different observable traits (phenotypes) in the offspring resulting from a genetic cross. These ratios are derived from the combinations of alleles and can provide evidence to support or refute genetic hypotheses. For example, in a dihybrid cross, the expected phenotypic ratio of 9:3:3:1 can help determine if the traits assort independently, which is a key aspect of Mendelian inheritance.