Final answer:
Results of a cross between AaBb and aabb plants yielding offspring that are either AaBb or aabb demonstrate complete dominance and independent assortment, indicating that one allele is dominant over the other and each pair segregates independently during gamete formation.
Step-by-step explanation:
If a cross is made between AaBb and aabb plants, and all of the offspring are either AaBb or aabb, these results are consistent with complete dominance. This means that one allele is dominant over the other, which is recessive, and the dominant allele hides the expression of the recessive allele in the phenotype.
The concepts of codominance and incomplete dominance do not apply here because in codominance, both alleles would be expressed equally, and in incomplete dominance, the phenotype would be a blend of both alleles, neither of which is the case according to the given results.