Three pairs of genes with two alleles each (A₁ and A₂, B₁ and B₂, and C₁ and C₂) control the height of a plant. The alleles of these genes have an additive relationship: Each copy of alleles A₁, B₁, and C₁ contributes 6 cm to plant height, and each copy of alleles A₂, B₂, and C₂ contributes 3 cm. What is the expected height of a plant with the genotype A₁A₂B₂B₂C₁C₂?

Key Concepts

Alleles and Genotypes

Alleles are different versions of a gene that can exist at a specific locus on a chromosome. In this context, A₁, A₂, B₁, B₂, C₁, and C₂ represent the alleles for three different genes controlling plant height. The genotype of an organism is the combination of alleles it possesses, which determines its traits, such as height in this case.

Additive Gene Interaction

Additive gene interaction occurs when the effects of different alleles contribute cumulatively to a phenotype. In this scenario, each allele contributes a specific amount to the plant's height: A₁ and C₁ add 6 cm, while A₂, B₂, and C₂ add 3 cm. This means that the total height can be calculated by summing the contributions of all alleles present in the genotype.

Calculating Phenotypic Expression

To determine the expected height of a plant based on its genotype, one must calculate the total contribution of each allele. By identifying the alleles present in the genotype A₁A₂B₂B₂C₁C₂ and applying the specified height contributions, one can derive the plant's expected height. This involves counting the number of each allele and multiplying by their respective height contributions.