This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics, Subject name: Pathology
ABO blood group inheritance is an example of: 
Select and explain. 
A. Codominance, B. Mitochondrial inheritence, C. Allelic exclusion, D. Sex-linked Inheritance
A: Codominance
Answer: A: Codominance 
Explanation: When both of the alleles of a gene pair contribute to the phenotype, this is called as codominance. Good examples of codominant inheritance are: Histocompatibility Blood group antigens