The red hair gene is recessive, not dominant. In order for a person to be born with red hair, he needs two copies of that gene for it to show up. The gene responsible for red hair is the MC1R gene.
Red hair is rare; just over 0.5 percent of people in the world are natural redheads. This would amount to only one in 200 people, or 40 million people worldwide. Ireland has the highest concentration of redheads; 10 percent of the Irish population has red hair. Around 40 percent of the Irish carry the red hair recessive gene. In Scotland, 13 percent of the population has red hair.