Final answer:
The more closely related two individuals are, the higher the probability that they will share MHC class I molecules, because of the genetic similarities they share, which is important for organ transplant compatibility.
Step-by-step explanation:
The question pertains to the Major Histocompatibility Complex (MHC) class I molecules, which play a crucial role in the immune response and organ transplantation compatibility among individuals. The more closely related two individuals are, the higher the probability is that they will share more MHC class I molecules in common. This is due to the genetic similarity that relatives share, leading to increased chances of matching MHC class I alleles which are crucial for transplant compatibility.
For example, a parent or sibling may be a more suitable donor for an organ transplant compared to an unrelated individual because they are more likely to match the recipient's MHC class I alleles. This is a result of the high polymorphism (variety) present in the MHC genes, making a match between unrelated individuals less common, which is why such matches often require searching through a worldwide database.