Correct Option: D. AS Explanation of the Correct Answer: To understand why the correct answer is D (AS), we need to delve into the genetics of hemoglobin and how traits are inherited.

1. Understanding the Genotypes:
2. The man has normal hemoglobin, which is represented by the genotype AA. This means he has two normal alleles for hemoglobin.
3. The woman has sickle-cell hemoglobin, represented by the genotype SS. This means she has two alleles for sickle-cell hemoglobin.
4. Sickle-Cell Trait:
5. The child has a sickle-cell trait, which is represented by the genotype AS. This means the child has one normal hemoglobin allele (A) and one sickle-cell allele (S). The presence of one normal allele (A) allows the child to have normal hemoglobin function, while the sickle-cell allele (S) does not fully express the sickle-cell disease phenotype.
6. Punnett Square Analysis:
7. To visualize the inheritance, we can use a Punnett square. The alleles from the parents are placed on the top and side of the square:
   • The father (AA) can only contribute an A allele.
   • The mother (SS) can only contribute an S allele.
8. The Punnett square would look like this:

A | A ---------------- S | AS | AS ---------------- S | AS | AS

• From this Punnett square, we see that all offspring (100%) will have the genotype AS. This confirms that the child has the sickle-cell trait.

Why the Other Options are Incorrect:

• Option A: AA
• This genotype indicates that the individual has two normal hemoglobin alleles. Since the mother contributes an S allele, it is impossible for the child to have the AA genotype. Therefore, this option is incorrect.
• Option B: OO
• This genotype does not relate to hemoglobin traits. The OO genotype typically refers to blood type (specifically type O blood) and is not relevant to the discussion of hemoglobin types. Thus, this option is not applicable and is incorrect.
• Option C: AO
• This genotype suggests that the individual has one normal hemoglobin allele (A) and an O allele. However, there is no O allele in the context of hemoglobin inheritance from the parents provided. The mother does not contribute an O allele, making this option incorrect.

Summary of Key Points:

• The child with sickle-cell trait has the genotype AS, inheriting one normal allele (A) from the father and one sickle-cell allele (S) from the mother.
• The Punnett square analysis confirms that all offspring from an AA father and an SS mother will have the AS genotype.
• Other options (AA, OO, AO) do not accurately represent the possible genotypes based on the parents' alleles.

This thorough understanding of inheritance patterns and the use of Punnett squares is crucial for mastering genetics in biology.