Which one of the following does NOT show non-allelic interaction?

Gene interactions can be broadly classified into two types: allelic (intragenic) and non-allelic (intergenic) interactions.

Allelic interactions occur between alleles of the same gene. Examples include incomplete dominance, co-dominance, and multiple alleles. In co-dominance, both alleles of a single gene are fully expressed in a heterozygote, making it a classic example of an allelic interaction.

Non-allelic interactions occur between alleles of different genes. Examples include epistasis, complementary genes, supplementary genes, and polygenic inheritance (polygenes).

Since co-dominance is an intragenic (allelic) interaction, it does not show non-allelic interaction.

Answer: Co-dominance