Hi there!

In incomplete dominance, the dominant trait is unable to express itself completely over the recessive trait. Thus, an intermediate trait is expressed. For example, in Antirrhinum, when red flowers (RR) and white (rr) flowers are crossed. The F1 progeny produced all pink flowers (Rr) instead of red flowers. Thus, it can be predicted that allele R is not completely dominant in heterozygous condition.

While in codominance, the two alleles of a gene equally express themeselves to contribute to the expression of a phenotype. Thus, the F1 progeny has characteristics of both alleles. For example, codominance in blood group AB.

Thanks