RADCLIFFE, IA—Despite its being the uncontrollable product of genetics and chance, Phil Schroeder's blood type is a frequent source of pride for the 26-year-old graphic designer. "I'm B-negative," said Schroeder, expecting to get a big reaction from coworker Mindy Tremont. "That's the second most rare after AB-negative." Schroeder, who has been known to high-five fellow B-negatives, went on to tell Tremont that individuals with Type B are said to be creative and excitable, prompting her to murmur, "Wow."