There is information that 45 percent of the world's population belongs to blood type O, so it is sometimes referred to as 'universal'. There are countries where some types of blood predominate over others, such as Norway and Finland, where the majority of the population belongs to group A. On the other hand, 100 percent of the natives of the American continent have the O group in their veins. However, the least common is one known as the Bombay blood type (subtype h-h), which was found in a Czechoslovak nurse in 1961 and a pair of American twins in 1968.
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