Final answer:
The inheritance pattern where heterozygous organisms show phenotypes with both alleles is codominance. Option (2) Codominance is the correct answer, as seen in the human AB blood type where both A and B alleles are expressed equally.
Step-by-step explanation:
Inheritance Patterns and Phenotypic Expression
The inheritance pattern in which heterozygous organisms exhibit a phenotype that includes both alleles is known as codominance. Unlike incomplete dominance, where the heterozygote displays an intermediate phenotype between the two homozygotes, codominance results in a phenotype that clearly shows both alleles. For instance, in human blood types, the AB blood group is a classic example of codominance. A person with AB blood type expresses both the A and the B alleles simultaneously, with neither allele completely masking the other.
Returning to the question, the correct option is (2) Codominance.
Examples of Codominance and Incomplete Dominance
An excellent real-world example of codominance is the ABO blood group system. The genotype of a person with type O blood, lacking both antigens, is ii, while the genotype(s) of a person with type AB blood, expressing both antigens, is IAIB. Comparatively, incomplete dominance is observed when a red-flowered plant is crossed with a white-flowered one, producing offspring with pink flowers, which is an intermediate phenotype.