Explain the following terms with example
Co-dominance
Co-dominance: When two alleles of a gene are both expressed equally in a heterozygote, and neither allele is dominant or recessive over the other. Both traits appear simultaneously in the organism.
Example: The ABO blood group system in humans, where alleles Iᴬ and Iᴮ are co-dominant. A person with genotype IᴬIᴮ expresses both A and B antigens on their red blood cells, resulting in blood group AB.
Incomplete dominance
Incomplete dominance: When the heterozygote exhibits a phenotype that is intermediate between the two homozygous parents. Neither allele is completely dominant, resulting in a blending of traits.
Example: In snapdragon flowers, when a homozygous red-flowered plant (RR) is crossed with a homozygous white-flowered plant (rr), the F₁ generation produces pink flowers (Rr) – an intermediate phenotype between red and white.
Explanation
This question tests understanding of two important exceptions to Mendel's Law of Dominance. Co-dominance involves both alleles being fully expressed simultaneously (like AB blood group), while incomplete dominance produces an intermediate phenotype in heterozygotes (like pink snapdragon flowers). Both concepts demonstrate that dominance is not always complete.