By now we have observed how homologous chromosomes separate during meiosis, and have learned to separate alleles when we determine the expected genetic makeup of offspring. Genes Code for Proteins Genes are sections of DNA that contains the information concerning the sequence of amino acids that should be assembled to make a particular polypeptide. The two forms look and act different resulting in an organisms different color or odor.
Many proteins serve as enzymes.
If an enzymes structure changes it cannot catalyze its particular reaction and that reaction will not take place. If an enzyme is missing because the gene that makes it fails to work, then the reaction that it catalyzes, and all reactions that depend on it stop.