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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
4. Hitchhiker's thumb (H) is dominant to no hitchhiker's thumb (h). A woman who does not have hitchhiker's thumb marries a man who is heterozygous for hitchhiker's thumb. What is the probable genotypic ratio of their children? (SC.912.L.16.1)

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1 point
0% Hh: 100% hh
50% Hh: 50% hh
75% Hh: 25% hh
100% Hh: 0% hh

1 answer

For the first question regarding which set of parents can most likely produce a child with type O blood, let's analyze the options:

  1. One parent with type AB blood, and the other parent with type A blood: The AB parent can donate either A or B alleles, and the A parent can either donate A or O. This cannot produce type O blood.

  2. One parent with type AB blood and the other parent with type O blood: The AB parent can donate either A or B alleles, and the O parent can only donate O. Thus, this combination cannot produce type O blood.

  3. One parent with heterozygous type A blood (genotype AO) and the other parent with type O blood (genotype OO): This combination can produce offspring with the following genotypes: AO (type A) and OO (type O). Therefore, this can produce a child with type O blood.

  4. One parent with homozygous type A blood (AA) and the other parent with homozygous type B blood (BB): This can only produce offspring with AB blood type (genotypes AA and BB), thus cannot produce type O blood.

Based on this analysis, the correct answer is one parent with heterozygous type A blood, and the other parent with type O blood.

For the second question about hitchhiker's thumb (H) being dominant to no hitchhiker's thumb (h), the genotypes of the parents are:

  • The woman who does not have hitchhiker's thumb must have the genotype hh.
  • The man who is heterozygous for hitchhiker's thumb has the genotype Hh.

We can set up a Punnett square:

         H      h
      ______________
   h |   Hh   |   hh   |
      ______________
   h |   Hh   |   hh   |
      ______________

From this Punnett square, we can see that:

  • 50% of the offspring are Hh (which have hitchhiker's thumb).
  • 50% of the offspring are hh (which do not have hitchhiker's thumb).

Therefore, the probable genotypic ratio of their children is 50% Hh: 50% hh.