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.

The F₁ progeny of this cross are allowed to self-fertilize. What is the expected phenotypic distribution among the F₂ progeny?

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 traits mask the expression of recessive ones. This framework is essential for predicting the outcomes of genetic crosses, such as the phenotypic ratios seen in offspring.

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, it allows for a visual representation of all possible combinations in the F1 and F2 generations. This tool is crucial for determining the expected phenotypic ratios, such as those resulting from the axial and terminal flower traits in the given question.

Phenotypic Ratios

Phenotypic ratios refer to the relative frequencies of different phenotypes in the offspring resulting from a genetic cross. In the context of the question, understanding how to calculate these ratios based on the dominant and recessive traits of the parent plants is key to predicting the distribution of flower and pod forms in the F2 generation. This concept is fundamental for interpreting the results of genetic experiments.