I have been saying multiple times on a couple science blogs that humans, as we presently know ourselves, will not colonize Mars.
Humans cannot live outside in the Marian environment without a “spacesuit” or something similar, and humans are not going to live as “colonizers” in protected enclosures above ground, below ground or in caves. That might have been fine for Neanderthals or earlier, not humans.
Mars will be for human scientist explorers, only, and their stays will be limited. That, and robotics, drones, satellites and such will satisfy the human need to explore. There is no driving need for genetic modifications of humans. It is only something that satisfies utopian scientific fantasies, not humanity.