Deep in a previously unexplored South American rain forest, a plant species was discovered with true-breeding varieties whose flowers were pink, rose, orange, or purple. A very astute plant geneticist made a single cross, carried to the F₂ generation, as shown: P₁: purple × pink F₁: all purple F₂: 27/64 purple 16/64 pink 12/64 rose 9/64 orange Based solely on these data, he proposed both a mode of inheritance for flower pigmentation and a biochemical pathway for the synthesis of these pigments. Carefully study the data. Create a hypothesis of your own to explain the mode of inheritance. Then propose a biochemical pathway consistent with your hypothesis. How could you test the hypothesis by making other crosses?

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 dominance of the purple flower trait over pink suggests a simple Mendelian inheritance pattern, where the purple allele is dominant and pink is recessive. The observed ratios in the F₂ generation can be analyzed to infer the genetic basis of flower color.

Phenotypic Ratios

Phenotypic ratios are the proportions of different observable traits in the offspring resulting from a genetic cross. The F₂ generation data shows a 27:16:12:9 ratio for purple, pink, rose, and orange flowers, respectively. This distribution can indicate the involvement of multiple alleles or genes, suggesting a more complex inheritance pattern than simple dominance, possibly involving epistasis or polygenic inheritance.

Biochemical Pathways

Biochemical pathways are sequences of chemical reactions occurring within a cell, leading to the synthesis of specific compounds, such as pigments. In the context of flower color, the pathway for pigment synthesis may involve multiple enzymes that convert precursor molecules into final pigment products. Understanding this pathway can help explain the observed flower colors and guide experiments to test the genetic hypothesis by manipulating specific genes or enzymes involved in pigment production.