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. Identify the number of different genotypes that are possible with these three genes.

Key Concepts

Alleles and Genotypes

Alleles are different versions of a gene that can exist at a specific locus on a chromosome. In this scenario, each gene (A, B, C) has two alleles (A₁/A₂, B₁/B₂, C₁/C₂). A genotype is the combination of alleles an organism possesses for a particular gene, which can be homozygous (two identical alleles) or heterozygous (two different alleles). Understanding how these combinations form is crucial for determining the total number of genotypes.

Additive Gene Interaction

Additive gene interaction occurs when the effects of different alleles contribute cumulatively to a phenotype, such as plant height in this case. Each allele contributes a specific amount to the trait, meaning that the total height can be calculated by summing the contributions from all alleles present. This concept is essential for understanding how multiple genes can influence a single trait and how to calculate the resulting phenotypic variations.

Combinatorial Genetics

Combinatorial genetics involves calculating the number of possible combinations of alleles from multiple genes. For each gene with two alleles, there are three possible genotypes (homozygous dominant, heterozygous, homozygous recessive). When considering multiple genes, the total number of genotypes is found by multiplying the number of genotypes for each gene, which is key to solving the question about the number of different genotypes possible with the three genes.