A 3-inch plant was crossed with a 15-inch plant, and all F₁ plants were 9 inches. The F₂ plants exhibited a 'normal distribution,' with heights of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15 inches.

What ratio will constitute the 'normal distribution' in the F₂?

Verified step by step guidance

1. span>Identify the parental phenotypes: A 3-inch plant and a 15-inch plant.</span
2. span>Observe the F₁ generation: All plants are 9 inches, indicating incomplete dominance or additive gene effects.</span
3. span>Note the F₂ generation: Heights range from 3 to 15 inches, suggesting polygenic inheritance with multiple genes contributing to height.</span
4. span>Understand 'normal distribution': In polygenic traits, the phenotypic distribution often follows a bell curve, with most individuals having intermediate phenotypes and fewer individuals at the extremes.</span
5. span>Determine the ratio: Calculate the expected phenotypic ratio by considering the number of contributing alleles and their combinations, which typically results in a 1:4:6:4:1 ratio for a trait controlled by two genes with additive effects.</span

Key Concepts

Normal Distribution

Normal distribution is a statistical concept where data points are symmetrically distributed around a mean, forming a bell-shaped curve. In genetics, traits often follow this distribution when influenced by multiple genes, leading to a range of phenotypes. The heights of the F₂ plants in this scenario suggest that multiple alleles contribute to the trait, resulting in a continuous variation of plant heights.

F₁ and F₂ Generations

The F₁ generation is the first filial generation resulting from a cross between two parental (P) plants, while the F₂ generation is produced by interbreeding F₁ individuals. In this case, the F₁ plants are all 9 inches tall, indicating a dominant trait, while the F₂ generation shows a range of heights, reflecting the segregation of alleles and the reappearance of the parental traits.

Phenotypic Ratio

Phenotypic ratio refers to the relative frequency of different phenotypes in a population. In the context of the F₂ generation, the normal distribution of plant heights suggests that the phenotypic ratio will not be a simple Mendelian ratio (like 3:1 or 9:3:3:1) but rather a continuous range of heights. This indicates polygenic inheritance, where multiple genes influence a single trait.