WASHINGTON (AP) — Scientists would gain vastly expanded capabilities to identify potentially deadlier mutations of the coronavirus under legislation advancing in Congress. The U.S. now maps only the genetic makeup of a minuscule fraction of positive virus samples, a situation some experts liken to flying blind. It means the true domestic spread of problematic mutations first identified in the United Kingdom and South Africa remains a matter of guesswork. Such ignorance could prove costly in the race to vaccinate Americans before virus variants become dominant here. The House COVID-19 relief bill would provide $1.75 billion for mapping virus genes, while a Wisconsin Democratic senator has introduced legislation to spend $2 billion.