When scientists first started mapping human genes, they estimated that there were about 2 million genes. By the late 1990s, it was thought that there were only 100,000 genes, and then that number shrank to 19,000 in 2001. Most scientists now believe that humans have about 21,000 genes.Which statement describes these estimates?

As scientists gathered more evidence and improved their methods, their estimates moved toward the current estimate of about 21,000 genes. The early estimate of 2 million was far off, while the later estimates of 19,000 and 21,000 were much closer. Therefore, the estimates became more accurate over time, which is choice A.

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