Question

multiple choice question
which reason best explains why the abo blood group is an example of multiple alleles and codominance?

• alleles ia and i are codominant, and allele ib is recessive to ia.
• alleles ia and ib are codominant and allele i is recessive to ia and ib.
• alleles ib and i are codominant, and allele ia is recessive to i and ib.
• alleles ia and ib are codominant and allele i is recessive to ib.

Explanation:

To determine the correct answer, we recall the principles of multiple alleles and codominance in the ABO blood group system. In the ABO system, there are three alleles: \( I^A \), \( I^B \), and \( i \). Codominance occurs when both \( I^A \) and \( I^B \) are present (resulting in blood type AB), meaning they are codominant. The allele \( i \) is recessive to both \( I^A \) and \( I^B \) (since \( I^A i \) gives type A and \( I^B i \) gives type B, while \( ii \) gives type O).

• The first option is incorrect because \( I^A \) and \( i \) are not codominant ( \( i \) is recessive to \( I^A \) ), and \( I^B \) is not recessive to \( I^A \).
• The second option correctly states that \( I^A \) and \( I^B \) are codominant and \( i \) is recessive to both.
• The third option is incorrect as \( I^B \) and \( i \) are not codominant, and \( I^A \) is not recessive to \( i \) or \( I^B \).
• The fourth option is incorrect because \( i \) is recessive to both \( I^A \) and \( I^B \), not just \( I^B \).

Answer:

B. Alleles \( I^A \) and \( I^B \) are codominant and allele \( i \) is recessive to \( I^A \) and \( I^B \).