A dark-red strain and a white strain of wheat are crossed and produce an intermediate, medium-red F₁. When the F₁ plants are interbred, an F₂ generation is produced in a ratio of 1 dark-red: 4 medium-dark-red: 6 medium-red: 4 light-red: 1 white. Further crosses reveal that the dark-red and white F₂ plants are true breeding

How many additive alleles are needed to produce each possible phenotype?

Key Concepts

Additive Alleles

Additive alleles are multiple alleles that contribute to a phenotype in a cumulative manner. In this context, each allele adds a specific amount of pigment to the wheat, resulting in varying shades of red. The more additive alleles present, the darker the phenotype, while fewer alleles lead to lighter shades. Understanding how these alleles interact is crucial for predicting the phenotypic ratios observed in the F₂ generation.

Phenotypic Ratios

Phenotypic ratios represent the relative frequencies of different phenotypes in a given generation. In this case, the F₂ generation exhibits a specific ratio of dark-red, medium-dark-red, medium-red, light-red, and white phenotypes. Analyzing these ratios helps in understanding the genetic basis of inheritance and the number of alleles involved in producing each phenotype, which is essential for answering the question.

True Breeding

True breeding refers to organisms that consistently produce offspring with a specific phenotype when self-fertilized or crossed with similar individuals. In the context of the dark-red and white F₂ plants being true breeding, it indicates that these plants have homozygous alleles for their respective traits. This concept is important for understanding the genetic stability of certain phenotypes and how they contribute to the overall inheritance patterns observed in the experiment.