What is an agent that can cause infections and diseases ?

Although at first it may seem like an antigen, it's a pathogen.

small, big, or no change could occur in the phenotype. it could cause something as simple as a cats ears to curl backwards or something as frighting as death. it could also occur in the protien-coding area and have an effect on that but no effect on the amino acids. what has to occur is a changing in the hox gene or the control gene.

i believe it would cause an increase of percipitation, though i could be wrong. so i would say b is the answer.