Multiple alleles and codominance are important concepts in genetics. The ABO blood groups represent a well-known example of these concepts. Answer the following questions to gain a greater understanding of these concepts:

• What blood type(s) can a child born to a mother with B- blood type and a father with A+ blood type have? Explain your answer fully. Be sure to focus on the concepts of dominant and recessive alleles, multiple alleles, and codominance in your explanation.

• Are there any special concerns this mother should consider?

• How do you think O can be the most common blood type when O is recessive?

• Describe another trait in humans that shows multiple alleles.

• Although the human population as a whole share the same 29 known blood systems, not all ethnic groups have the same ratios of blood types in their populations. Discuss this fact from an evolutionary perspective.