Homozygous dominant in ABO: two identical dominant alleles Steps:

• Recall ABO alleles: I^A and I^B dominant/codominant, I^O recessive.
• Define homozygous dominant as genotype with two copies of same dominant allele (I^A or I^B).
• Identify options with matching alleles: A has two I^A, C has two I^B.
• Select C as example of homozygous dominant for I^B allele.

Why C is correct:

• I^B I^B consists of two identical dominant I^B alleles, per Mendelian genetics definition of homozygosity for a dominant trait.

Why the others are wrong:

• A. I^A I^A is homozygous but for I^A allele, not I^B.
• B. I^A I^B is heterozygous with two different codominant alleles.
• D. I^A I^O is heterozygous, pairing dominant I^A with recessive I^O.

Final answer: C