Two pure-breeding wheat strains, one producing dark red kernels and the other producing white kernels, are crossed to produce F₁ with pink kernel color. When an F₁ plant is self-fertilized and its seed collected and planted, the resulting F₂ consists of 160 plants with kernel colors as shown in the following table.

Using clearly defined allele symbols of your choice, give genotypes for the parental strains and the F₁. Describe the genotypes that produce the different phenotypes in the F₂.

Verified step by step guidance

1. Step 1: Define allele symbols to represent the genetic basis of kernel color. For example, use 'A' and 'a' for one gene, and 'B' and 'b' for another gene. Assume that kernel color is determined by two genes, each with two alleles, where dominant alleles contribute to darker colors.
2. Step 2: Assign genotypes to the parental strains. The dark red strain could be homozygous dominant for both genes (AABB), while the white strain could be homozygous recessive for both genes (aabb). This ensures pure-breeding parental strains.
3. Step 3: Determine the genotype of the F₁ generation. Crossing AABB (dark red) with aabb (white) produces heterozygous offspring (AaBb), which exhibit the intermediate phenotype of pink kernel color due to incomplete dominance or additive effects.
4. Step 4: Describe the genotypes that produce the different phenotypes in the F₂ generation. When F₁ plants (AaBb) are self-fertilized, the offspring exhibit a variety of genotypes due to independent assortment and segregation. For example: AABB (dark red), AaBB or AABb (red), AaBb or Aabb or aaBb (pink/light pink), and aabb (white).
5. Step 5: Explain how the phenotypic ratios in the F₂ generation correspond to the genotypes. Use a Punnett square to predict the distribution of genotypes and phenotypes. The observed kernel color numbers (e.g., 9 white, 12 dark red, etc.) can be compared to the expected ratios based on Mendelian inheritance and additive effects of the alleles.

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 involves understanding dominant and recessive alleles, where dominant alleles mask the expression of recessive ones. This framework helps explain the inheritance patterns observed in the F₁ and F₂ generations of the wheat strains, particularly in determining the phenotypic ratios.

Alleles and Genotypes

Alleles are different versions of a gene that can exist at a specific locus on a chromosome. In this scenario, the dark red and white kernel colors are determined by specific alleles, which can be represented by symbols (e.g., R for red and r for white). The genotype of an organism is the combination of alleles it possesses, which directly influences its phenotype, or observable traits.

Phenotypic Ratios

Phenotypic ratios describe the relative frequencies of different phenotypes in a population resulting from genetic crosses. In the F₂ generation, the observed phenotypic ratios can be analyzed to infer the underlying genotypes. For example, the presence of pink, light pink, and red kernels suggests a blend of dominant and recessive alleles, which can be quantified to understand the inheritance pattern and validate Mendelian predictions.