A multi-subunit protein is a good example of a quaternary-structure protein. A quaternary structure protein is often defined as a unit composed of different polypeptide sequences or chains (often called subunits). The most common interactions observed in these conformations are chemical interaction between the “R” groups in the amino acids that composed the proteins. These interactions are mostly weak interactions (such as London dispersion forces and hydrogen bonds). Therefore, option D is correct.
Have you ever done a Punnett Square? This question forces you to make one. If your cross a homozygous type A (AA) and homozygous type O (OO) you should get 100% AO. Understanding genetics, an AO gene means a type A blood. Therefore, it's 100% type A blood (AO).
