A true-breeding purple-leafed plant isolated from one side of El Yunque, the rain forest in Puerto Rico, was crossed to a true-breeding white variety found on the other side. The F₁ offspring were all purple. A large number of F₁ x F₁ crosses produced the following results: purple: 4219 white: 5781 (Total = 10,000) Propose an explanation for the inheritance of leaf color. As a geneticist, how might you go about testing your hypothesis? Describe the genetic experiments that you would conduct.

Verified step by step guidance

1. <insert step 1: Begin by identifying the phenotypes and genotypes involved in the problem. The true-breeding purple-leafed plant and the true-breeding white variety suggest homozygous genotypes.>
2. <insert step 2: Since the F₁ generation is all purple, this indicates that the purple trait is dominant over the white trait. Assign a dominant allele (P) for purple and a recessive allele (p) for white.>
3. <insert step 3: The F₁ generation, being all purple, would have the genotype Pp. When these F₁ plants are crossed (Pp x Pp), the expected phenotypic ratio in the F₂ generation should be 3:1 for a single gene with complete dominance.>
4. <insert step 4: Calculate the expected numbers of purple and white plants in the F₂ generation based on the 3:1 ratio. Compare these expected numbers to the observed numbers (4219 purple and 5781 white) to see if they fit the expected Mendelian ratio.>
5. <insert step 5: Conduct a chi-square test to statistically evaluate the fit between the observed and expected ratios. This will help determine if the deviation from the expected 3:1 ratio is due to chance or if another genetic model might be more appropriate.>

Key Concepts

Mendelian Inheritance

Mendelian inheritance refers to the principles of heredity established by Gregor Mendel, which describe how traits are passed from parents to offspring through dominant and recessive alleles. In this case, the purple leaf color is likely a dominant trait, as all F₁ offspring exhibited purple leaves when crossed with a true-breeding white variety. Understanding these principles helps explain the observed phenotypic ratios in the F₂ generation.

Phenotypic Ratio

The phenotypic ratio is the ratio of different phenotypes observed in the offspring of a genetic cross. In this scenario, the F₂ generation shows a ratio of approximately 3:1 (purple to white), which is characteristic of a monohybrid cross involving a dominant and a recessive trait. This ratio supports the hypothesis that the purple leaf color is dominant over the white color.

Genetic Testing and Experimental Design

To test the hypothesis regarding the inheritance of leaf color, a geneticist could conduct further crosses, such as backcrossing F₁ individuals with the white parent to observe the resulting offspring's phenotypes. Additionally, performing a test cross with known homozygous individuals can help confirm the genotype of the purple-leafed plants. Analyzing the offspring ratios from these experiments will provide further evidence for the inheritance pattern.