A parent with the blood type A (genotype AO) and a parent with blood type B (genotype BO) have children with blood types A, B, and AB. What type of inheritance pattern is shown by the child with type AB blood and why?

Co-dominance because he expresses both of the alleles simultaneously

Explanation:

The ABO blood group system is used by humans. This blood group type is controlled by multiple alleles. Alleles A and B are both dominant over allele O but are co-dominant. Co-dominance is a type of inheritance pattern in which two alleles of a gene both express themselves i.e. neither is recessive.

This is the case of this family whose parents have a genotype of AO (blood type A) and BO (blood type B) respectively. The children have blood types A, B, and AB. However, the child with genotype AB possesses both the A and B allele, which are both expressed in his blood group (phenotype), hence, it can be said that the child is exhibiting CO-DOMINANCE for the blood group trait.

gametes or germ cells are haploid cells (example: sperm and ova) containing only one set (or n) number of chromosomes and autosomal or somatic cells are diploid cells containing 2n number of chromosomes.