When the heterozygous genotype results in a phenotype where two alleles are blended together.
Incomplete Dominance
Codominance
Linked Genes
Polygenic Inheritance
The Correct Answer and Explanation is:
The correct answer is Incomplete Dominance.
Incomplete dominance is a genetic phenomenon where the phenotype of a heterozygous individual is a blend or intermediate of the two alleles from the parents. This differs from complete dominance, where the dominant allele completely masks the effect of the recessive allele. In incomplete dominance, neither allele is completely dominant, and the result is a phenotype that is a mixture of both traits.
A classic example of incomplete dominance is the flower color in snapdragons (Antirrhinum majus). When a red-flowered snapdragon (RR) is crossed with a white-flowered snapdragon (WW), the resulting offspring, which are heterozygous (RW), will have pink flowers. In this case, the red allele (R) and the white allele (W) do not dominate each other, but rather combine to produce an intermediate pink color.
The underlying cause of incomplete dominance lies in the molecular action of the alleles. The red allele may encode an enzyme that produces pigment, while the white allele may produce a nonfunctional version of this enzyme. In a heterozygous individual (RW), only one functional enzyme may be produced, leading to a reduced amount of pigment and resulting in an intermediate color (pink).
This genetic pattern is different from codominance, where both alleles contribute equally and visibly to the phenotype without blending. An example of codominance is seen in human blood types: the A and B alleles are codominant, meaning an individual with AB blood type expresses both the A and B antigens on the surface of red blood cells.
Linked genes refer to genes located close together on the same chromosome, which tend to be inherited together, and polygenic inheritance involves multiple genes contributing to a single trait, such as skin color or height. Neither of these describes the blending of alleles in the way incomplete dominance does.