An influential science advisory group formed by the National Academy of Sciences and the National Academy of Medicine on Tuesday lent its support to a once-unthinkable proposition: the modification of human embryos to create genetic traits that can be passed down to future generations.

This type of human gene editing has long been seen as an ethical minefield. Researchers fear that the techniques used to prevent genetic diseases might also be used to enhance intelligence, for example, or to create people physically suited to particular tasks, like serving as soldiers.

The advisory group endorsed only alterations designed to prevent babies from acquiring genes known to cause “serious diseases and disability,” and only when there is no “reasonable alternative.” The report provides an explicit rationale for genetic research that the federal government has avoided supporting until now, although the work is being pursued in countries like Sweden and China.

So-called germ line engineering might allow people to have biological children without fear that they have passed on the genes for diseases like Huntington’s, Tay-Sachs and beta thalassemia, and without discarding embryos carrying the disease-causing mutations, as is often done now. Though such cases are likely to be rare, the report says they should be taken seriously.