Question

You and a classmate are discussing early experiments in genetics, and you state that Avery, MacLeod, and McCarty provided the first evidence that DNA carries genetic information. Your classmate argues that Griffith was the first to demonstrate this. Which statement best defends your argument?

1) Although Griffith first demonstrated transformation, Avery, MacLeod, and McCarty provided evidence that DNA rather than protein or RNA was the transforming agent.
2) Avery, MacLeod, and McCarty worked with purified DNA extracts while Griffith worked with bacterial strains.
3) Enzymes were used in the experiments carried out by Avery, MacLeod, and McCarty while Griffith transformed cells chemically or by using heat.
4) Because Avery, MacLeod, and McCarty did their experiments after those done by Griffith, they had much more information regarding the structure and function of DNA.
5) DNA used by Avery, MacLeod and McCarty was extracted solely from transformed strains of pneumococci, while Griffith used native pneunococcal strains.

Answer 1

Avery, MacLeod, and McCarty provided conclusive evidence that DNA is the carrier of genetic information by demonstrating that only the destruction of DNA, not other components like RNA or proteins, could stop the transforming ability of the bacterial mixture.

Step-by-step explanation:

The statement that best defends the argument that Avery, MacLeod, and McCarty provided the first evidence that DNA carries genetic information is: 'Although Griffith first demonstrated transformation, Avery, MacLeod, and McCarty provided evidence that DNA rather than protein or RNA was the transforming agent.' This is because their experiments took the findings of Griffith a step further by isolating and testing different molecular components of heat-killed S-strain bacteria for their ability to transform R-strain bacteria. Their use of enzyme treatments to specifically degrade each component revealed that only when DNA was destroyed did the transforming ability of the mixture cease, leading to the conclusion that DNA was the substance responsible for transformation, supporting the idea that DNA is the carrier of genetic information.