The main immediate use of a map of the 100 000 or so genes on the 46 human chromosomes is that we would be better at pinpointing the causes of inherited diseases. For instance, if we already had the map it would have taken very little time to narrow down the genetic cause of cystic fibrosis once we knew its biochemical symptoms. None of the first 3 options make any sense whilst we can already sex an embryo by looking at its sex chromosomes.
