Please help me determine this sci-fi story: Read it, think it was a stand-alone novel, in the late 1980's - and I don't think it was all that old then. The main character was solitary, at start of story foraging in a snowed-under grocery store. The plot involved his DNA containing some kind of hidden message or instructions, put in his ancestor(s) many thousands of years earlier by a (crashed?) alien scientist. Now, others ("bad guys") are looking for it, creating an artificial ice age (via a dust cloud between earth and the sun, if memory serves) to drive humans to the equator, where they "help" with humanitarian efforts while actually looking for this DNA code. Main character's name may or may not be Starkman or Starmann; I seem to recall that his eyes were an unusual colour, maybe yellow or amber. I read a ton of sci-fi stuff back then, so I may be getting things mixed up after this long, but the main plot is right. I'm in Canada, if that helps/matters.
Found it. The Chromosomal Code
It has the same hero name, ice age, aliens and a physical deformity.
A sudden ice age has driven Earth's population into the tropics, except for a few die-hards eking out a tenuous existence scavenging the snow-covered ruins of civilization. One such straggler is John Starkman, making his home in the frozen wastes of western Pennsylvania. Already an outcast because of a certain physical peculiarity, he saw no reason to join his neighbors in fleeing south. Then one day a spaceship comes to collect him and the other stragglers, and Starkman discovers there have been other changes besides the ice age. Aliens have landed on Earth. They say they've come to help -- but what do they really want? And why are they interested in him?