Fill in each blank with the word that best completes the sentence. 4. Many genes do not follow the simple patterns of inheritance that Mendel described. In some cases, both genes are fully expressed in the heterozygote. This is called In other cases, two traits appear to blend in what is called Some traits are governed by a num- alleles. For example, the four groups are controlled by three alleles instead of two. ber of different alleles, called human Biology: Visualizing Life Reteaching: CHAPTER 7 13​