The letters in the diagram below represent genes on a particular chromosome.
Gene B contains the code for an enzyme that cannot be synthesized unless gene A is also active. Which statement best explains why this can occur?
(1) A hereditary trait can be determined by more than one gene.
(2) Genes are made up of double-stranded segments of DNA.
(3) All the genes on a chromosome act to produce a single trait.
(4) The first gene on each chromosome controls all the other genes on the chromosome.