Genes.
"Do allergies pass on with generations?" She asked to keep her hope bright. Looking straight into doctor Jackson's eyes.
"Yes, they can. It is very common in generations that they have the same face as their parents, allergies, chronic diseases, few habits, learning ability, smartass. Everything that parents or grandparents have can be passed to the next generation."
As doctor Jackson cleared her doubt, the happiness seemed unending for her. Her heartfelt relief thinking that her suspicion about Xiao Xing as her grandson was correct even the reports were not so bright. Then she told him about Xiao Xing's allergy.
"You know, his father was allergic to Pollard fish and he is too." She spoke smiling.
"See, I told you it can happen. You know genes are miracles in the human body. They can pass anything to each generation. They decide what you are going to become in your life. Your face, your body, your nature everything, they decide."