The sentence that best helps develop the idea expressed in paragraph 2 is:
"Thanks to this analysis, the researchers were able to narrow down their original list of 3,000 genes to 43 specific sequences that might have contributed to Lonesome George’s long, disease-free life."
This sentence directly connects the study's achievements to understanding the genetic factors that contribute to longevity, reinforcing the main idea established in paragraph 2 regarding the researchers' goals with Lonesome George's genetic material.