You have two true-breeding rose bushes, one with red flowers and one with white flowers. A cross between these two roses yields a bush with white flowers that have red splotches. What condition does this demonstrate?

Codominance is a relationship between two versions of the same gene, called alleles. Individuals receive an allele from each parent and if the alleles are different, the dominant allele will normally be expressed, while the effect of the other allele (called recessive) is masked. However during codominance, the two allele genes are expressed, but without mixing.

A true-breeding organism is one that only passes down certain phenotypic traits to the offspring. So the organism is homozygous for every trait and they have identical alleles for specified traits, which are homozygous dominant or recessive.

The red flower could be homozygous dominant (AA) while the white flower could be homozygous recessive (aa). Then 100% of the offspring will be Aa, and since A (the dominant allele which masks the effects of the recessive allele) is red, then we would expect 100% of red flowers. However since they are white with red splotches, then this is an example of codominance.