The ABO blood group system illustrates

  • A. a single pair of alleles at one locus
  • B. two separate genes on two chromosomes
  • C. sex linked inheritance
  • D. multiple alleles, three of which exist at one locus

Explanation

The gene has three alleles in the population, I A, I B and i, though any one individual carries only two of them, and this is the definition of multiple allelism. The three alleles combine into six genotypes producing four phenotypes. The locus is on an autosome, so the trait appears equally in men and women and has nothing to do with sex linkage.

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