An allele that is will be expressed only if it is present on both chromosomes of a homologous pair.

answer; i believe that the correct answer is(d) nondisjunction during meiosis;

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.

affects the water bodies: excessive use of fertilizers causes eutrophication. the fertilizers which are used on plants affect the quality of land on which it is used, further causing erosion of soil. the fertilizers used on plants contain harmful chemical fumes which affect the environment.