Two homozygous blood type A parents have a blood type O child. Which of the following is the best explanation for this?Group of answer choicesBoth parents must be hH at H locus.Both parents must be HH at the H locus.Mom is heterozygous at the H locus, but the father is homozygous dominant at the H locus.Dad is heterozygous at the H locus, but the mom is homozygous dominant at the H locus.

The best explanation for two homozygous blood type A parents having a blood type O child is that both parents must be hH at the H locus.

Here's why:

The ABO blood type is determined by the ABO gene, which has three alleles: A, B, and O. The A and B alleles are co-dominant, and the O allele is recessive.

In this case, both parents are homozygous for the A allele, meaning they have two A alleles each.

However, there's another gene, the H gene, that can affect the expression of the ABO gene. The H gene has two alleles: H (dominant) and h (recessive).

If a person is homozygous for the h allele (hh), they will have the O blood type, regardless of what alleles they have at the ABO locus. This is because the h allele prevents the A and B alleles from being expressed.

So, if both parents are heterozygous at the H locus (hH), they can each pass on an h allele to their child. The child would then be homozygous for the h allele (hh) and have the O blood type, even though they have two A alleles at the ABO locus.

This is the only way two homozygous blood type A parents could have a blood type O child.