Genetics Extensions of Mendelian Inheritance Practice Test 2026 – Your All-In-One Guide to Master Exam Success!

When a trait is considered to be codominant, it means that two different alleles for a gene are expressed independently and simultaneously in the phenotype. This is distinct from complete dominance, where one allele completely masks the effect of another. In codominance, both traits can be observed equally and distinctly in the organism. A classic example of this is in certain blood types, such as AB blood type, where both A and B alleles are fully expressed and neither is recessive.

For instance, in a flower, if one allele codes for red and another for white, a codominant expression would result in flowers with both red and white patches rather than just one color dominating. This independent expression of both traits is the hallmark of codominance. The other choices describe differentiation from codominance, where only one trait shows up, dominance affects the expression unevenly, or all traits are hidden and recessive.