Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

Which of the following represents incomplete dominance?

1. One trait completely masks another

2. Traits blend together resulting in a third phenotype

3. A trait is never expressed

4. Dominant and recessive traits are equally expressed

The correct answer is: Traits blend together resulting in a third phenotype

The concept of incomplete dominance occurs when neither allele in a heterozygote completely masks the other, resulting in a blending of traits. In this scenario, the offspring exhibit a phenotype that is a combination of the two parental traits, rather than displaying one trait over the other. For example, if a red flower (RR) is crossed with a white flower (WW), the resulting offspring may produce pink flowers (RW), which showcase a blend of the red and white traits. This blending differentiates incomplete dominance from complete dominance, where one trait fully overshadows another, leading to only the dominant phenotype being expressed. Incomplete dominance is followed by a mix that can facilitate the emergence of a new, distinct phenotype that is different from both parents.