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Alleles for the A and B blood cell antigens are codominant. The condition where no antigens are present on the blood cells (type O blood) is a recessive trait. Which set of parents can most likely produce a child with type O blood? (SC.912.L.16.1)

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1 point
one parent with type AB blood, and the other parent with type A blood
one parent with type AB blood and the other parent with type O blood
one parent with heterozygous type A blood, and the other parent with type O blood
one parent with homozygous type A blood, and the other parent with homozygous type B blood

1 answer

To produce a child with type O blood (which is represented by the genotype \(ii\)), both parents must contribute an allele that is recessive, meaning they must both carry at least one allele for type O blood.

Here’s the breakdown of the potential parent combinations:

  1. One parent with type AB blood (genotype \(IAIB\)), and the other parent with type A blood (could be \(IAIA\) or \(IAi\)): This combination cannot produce a type O child. The AB parent cannot contribute an O allele.

  2. One parent with type AB blood (genotype \(IAIB\)) and the other parent with type O blood (genotype \(ii\)): This cannot produce a type O child either, as the AB parent cannot contribute O.

  3. One parent with heterozygous type A blood (genotype \(IAi\)), and the other parent with type O blood (genotype \(ii\)): This combination can produce a type O child. The A parent can pass down either an \(IA\) or \(i\), while the O parent can only pass down an \(i\). The possible offspring could be \(IAi\) (type A) or \(ii\) (type O).

  4. One parent with homozygous type A blood (genotype \(IAIA\)), and the other parent with homozygous type B blood (genotype \(IBIB\)): This combination cannot produce a type O child, as neither parent can pass an O allele.

Given this analysis, the answer is:

One parent with heterozygous type A blood, and the other parent with type O blood.