In pea plants, plant height, seed shape, and seed color are governed by three independently assorting genes. The three genes have dominant and recessive alleles, with tall (T) dominant to short (t), round (R) dominant to wrinkled (r), and yellow (G) dominant to green (g).


If a true-breeding tall, wrinkled, yellow plant is crossed to a true-breeding short, round, green plant, what phenotypic ratios are expected in the F₁ and F₂?

Verified step by step guidance

1. Step 1: Identify the genotypes of the parent plants. A true-breeding tall, wrinkled, yellow plant has the genotype TTrrGG, while a true-breeding short, round, green plant has the genotype ttRRgg. True-breeding means the plants are homozygous for their respective traits.
2. Step 2: Determine the F₁ generation genotype. Since the parents are homozygous for each trait, all F₁ offspring will be heterozygous for all three traits. The genotype of the F₁ generation will be TtRrGg.
3. Step 3: Predict the phenotypes of the F₁ generation. Each heterozygous genotype expresses the dominant phenotype. Therefore, all F₁ plants will be tall, round, and yellow.
4. Step 4: Use a Punnett square to analyze the F₂ generation. For the F₂ generation, each gene will segregate independently according to Mendel's law of independent assortment. Create a 4x4 Punnett square for each gene (T/t, R/r, G/g) to determine the combinations of alleles in the F₂ generation.
5. Step 5: Calculate the phenotypic ratios in the F₂ generation. Combine the results from the three Punnett squares to determine the phenotypic ratios for plant height, seed shape, and seed color. Since each gene segregates independently, multiply the probabilities of each phenotype to find the overall phenotypic ratio in the F₂ generation.

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 includes concepts such as dominant and recessive alleles, which determine the phenotype of an organism. In this case, the traits of plant height, seed shape, and seed color are governed by specific alleles that follow Mendel's laws of segregation and independent assortment.

Phenotypic Ratios

Phenotypic ratios refer to the relative frequencies of different phenotypes in the offspring resulting from a genetic cross. In this scenario, the expected phenotypic ratios in the F₁ and F₂ generations can be calculated using Punnett squares, which illustrate the combinations of alleles from the parents. Understanding these ratios helps predict the distribution of traits in the offspring.

Independent Assortment

The principle of independent assortment states that alleles for different traits segregate independently of one another during gamete formation. This means that the inheritance of one trait does not affect the inheritance of another. In the context of the question, the three traits (height, seed shape, and seed color) assort independently, allowing for a variety of combinations in the offspring when the two true-breeding plants are crossed.