ABSTRACT
The form of dominance depends on how the alleles for a particular gene interact with one another to produce a phenotype. The three basic forms of dominance are complete dominance, incomplete dominance, and codominance. Incomplete or partial dominance occurs when a heterozygous individual shows a totally new trait that is not seen in either parent. In codominance, neither allele is dominant over the other, but the two traits do not blend. In humans, the rare MN blood type is controlled by codominance. The basic types of dominance deal with one gene and only two possible alleles. Even if an individual's genes or alleles are unknown, it is fairly simple to determine which form of dominance they show. Blue bugs, yellow bugs, and blue-and-yellow bugs would indicate that the trait was controlled by codominance. Gregor Mendel's genes showed simple or complete dominance because one allele was always completely dominant over the other.
