In a series of crosses between two true-breeding strains of peaches, the F₁ generation was uniform, producing 30-g peaches. The F₂ fruit mass ranges from 38 to 22 g at intervals of 2 g.
Using gene symbols of your choice, give the genotypes of the parents and the F₂.

Verified step by step guidance

1. Step 1: Identify the inheritance pattern. The problem suggests quantitative inheritance, where multiple genes contribute to the trait (fruit mass). This is typical of polygenic traits, which show continuous variation.
2. Step 2: Assign gene symbols. Let’s assume two loci (A and B) control fruit mass, with each dominant allele (A or B) contributing 2 g to the base mass. The recessive alleles (a and b) contribute 0 g. The base mass is 22 g, and the maximum mass is 38 g.
3. Step 3: Determine the genotypes of the parents. Since the parents are true-breeding strains, one parent must be homozygous dominant (AABB) and the other homozygous recessive (aabb). This ensures the F₁ generation is uniform and heterozygous (AaBb).
4. Step 4: Analyze the F₂ generation. The F₁ individuals (AaBb) are self-crossed, producing offspring with combinations of alleles at both loci. Use a Punnett square to determine all possible genotypes and their corresponding phenotypes (fruit mass).
5. Step 5: Calculate the phenotypic range. Each dominant allele adds 2 g to the base mass of 22 g. For example, AABB contributes 8 g (22 + 8 = 38 g), AaBb contributes 4 g (22 + 4 = 30 g), and aabb contributes 0 g (22 g). List all possible genotypes and their associated fruit masses.

Key Concepts

True-breeding Strains

True-breeding strains are organisms that, when mated, produce offspring that are identical to themselves for specific traits. In genetics, this means that the parents are homozygous for the traits being studied, ensuring that the F₁ generation will display a uniform phenotype, as seen in the 30-g peaches.

F₁ and F₂ Generations

The F₁ generation is the first filial generation resulting from a cross between two true-breeding parents. In this case, the F₁ peaches are uniform at 30 g. The F₂ generation arises from self-fertilizing the F₁ individuals, leading to a phenotypic range, as observed with fruit masses ranging from 22 g to 38 g.

Genotype and Phenotype

Genotype refers to the genetic makeup of an organism, while phenotype is the observable physical or biochemical characteristics. In this scenario, the genotypes of the parents can be represented as homozygous (e.g., AA and aa), leading to a specific phenotype in the F₁ and a range of phenotypes in the F₂, reflecting the underlying genetic variation.