In a chemical reaction, reactants contact each other, bonds between atoms in the reactants are broken, and atoms rearrange and form new bonds to make the products.
They are like that because they can't always be faulty and may have at least some spark of truth to this theory also as stated earlier a theory in scientific terms is just an observation so it can't really be turned down hence theory.
T cells
The immune response to a transplanted organ consists of both cellular (lymphocyte mediated) and humoral (antibody mediated) mechanisms. Although other cell types are also involved, the T cells are central in the rejection of grafts. The rejection reaction consists of the sensitization stage and the effector stage.
No genes make up chromosomes. Chromosomes contain DNA sequences and specific sequences aka genes make specific traits.
