In 1944, the research team of Avery, McCarty, and MacLeod purified an extract from virulent pneumococcal bacteria. This extract was treated with various enzymes that either degraded proteins, RNA, lipids, or carbohydrates. This mixture was combined with nonvirulent bacteria that normally formed rough colonies. After mixing, the nonvirulent bacteria then became able to form smooth colonies. This change from rough to smooth colonies did not occur when, instead, the DNA was broken down by enzymes.
Which of the following major concepts of genetics was illustrated in the experiment by Avery, McLeod, and McCarty?