In pea plants, the appearance of flowers along the main stem is a dominant phenotype called 'axial' and is controlled by an allele T. The recessive phenotype, produced by an allele t, has flowers only at the end of the stem and is called 'terminal.' Pod form displays a dominant phenotype, 'inflated,' controlled by an allele C, and a recessive 'constricted' form, produced by the c allele. A cross is made between a pure-breeding axial, constricted plant and a plant that is pure-breeding terminal, inflated.

If the plants with terminal flowers produced by the cross in part (c) are saved and allowed to self-fertilize, what is the expected phenotypic distribution among the progeny?

Key Concepts

Dominant and Recessive Alleles

In genetics, alleles are different forms of a gene that can exist at a specific locus on a chromosome. Dominant alleles, represented by uppercase letters (e.g., T for axial flowers), mask the expression of recessive alleles, represented by lowercase letters (e.g., t for terminal flowers). In a heterozygous genotype, the dominant phenotype is expressed, while the recessive phenotype only appears in homozygous recessive individuals.

Punnett Square

A Punnett square is a diagram used to predict the genotypes and phenotypes of offspring from a genetic cross. By organizing the alleles of the parents along the top and side of a grid, one can visualize the possible combinations of alleles in the progeny. This tool is essential for determining the expected ratios of different phenotypes in the offspring, especially in dihybrid crosses involving two traits.

Self-Fertilization

Self-fertilization occurs when a plant's pollen fertilizes its own ovules, leading to the production of seeds from the same genetic material. In the context of the question, the terminal-flowered progeny from the initial cross will self-fertilize, allowing for the examination of the segregation of alleles in the next generation. This process is crucial for understanding inheritance patterns and predicting the phenotypic ratios of the resulting offspring.