What is the inheritance pattern where both alleles are expressed?

The correct answer is codominance.

Explanation:

Codominance signifies an association between the two versions of a gene. An individual attains one version of a gene known as allele from each of the parents. If the alleles are distinct, the dominant allele generally will get expressed, while the influence of the other allele, known as recessive, will get suppressed.  

However, in the phenomenon known as codominance, neither of the alleles is recessive, and both the alleles' phenotype get expressed. In general, codominance signifies that neither of the alleles can hide the expression of the other one. For example, ABO blood group in humans is an illustration of codominance, in which both the alleles A and B get expressed.  

one characteristic that is shared by all is a soft body. many

of these invertebrate animals also have an outer shell to protect their

body. oysters, clams, snails, and mussels are all mollusks. so are octopuses, squids, and slugs. mollusks live on land and in freshwater.