A cross between a spicy variety of Capsicum annum pepper and a sweet (nonspicy) variety produces  progeny plants that all have spicy peppers. The  are crossed, and among the  plants are 56 that produce spicy peppers and 20 that produce sweet peppers. Dr. Ara B. Dopsis, an expert on pepper plants, discovers a gene he designates Pun1 that he believes is responsible for spicy versus sweet flavor of peppers. Dr. Dopsis proposes that a dominant allele P produces spicy peppers and that a recessive mutant allele p results in sweet peppers.

Are the data on the parental cross and the F₁ and F₂ consistent with the proposal made by Dr. Dopsis? Explain why or why not, using P and p to indicate probable genotypes of pepper plants.

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. A dominant allele, represented by a capital letter (e.g., P), masks the effect of a recessive allele (e.g., p) when both are present in a heterozygous individual. This means that if an organism has at least one dominant allele, the dominant trait will be expressed in the phenotype, while the recessive trait will only be expressed if the organism has two copies of the recessive allele.

Punnett Square and Mendelian Inheritance

A Punnett square is a diagram used to predict the genotypes of offspring from a genetic cross. It illustrates how alleles from each parent combine during fertilization. According to Mendelian inheritance, the ratio of phenotypes in the offspring can be predicted based on the genotypes of the parents. In this case, the expected ratios of spicy to sweet peppers can be calculated using the proposed genotypes of the parental and F1 generations.

Phenotypic Ratios in F2 Generation

The F2 generation refers to the second filial generation, which results from crossing two F1 individuals. In a typical monohybrid cross involving one dominant and one recessive trait, the expected phenotypic ratio in the F2 generation is 3:1, where three offspring exhibit the dominant trait and one exhibits the recessive trait. Analyzing the observed phenotypic ratios in the F2 generation of the pepper plants will help determine if they align with Dr. Dopsis's hypothesis regarding the Pun1 gene.