Final answer:
If disorders have a shared genetic basis, we would expect correlated polygenic risks, with a higher likelihood of one disorder indicating increased risk for the other. However, actual polygenic risk would depend on the specific genetic variants and their interactions with environmental factors.
Step-by-step explanation:
If two disorders have a shared genetic basis, we would expect them to have correlated polygenic risks. This means that individuals who are genetically predisposed to one disorder might also have a higher risk for the other, due to overlapping sets of multiple genes (polygenes) that contribute to the etiology of both conditions. For example, polygenic diseases such as heart disease or diabetes are influenced by the combined effect of genes and environmental factors like diet. In contrast, disorders like cystic fibrosis, caused by a recessive allele of a single gene on an autosome, follow Mendelian inheritance patterns. However, most diseases are not determined by a single gene. When considering polygenic disorders, analyzing an individual's genome can provide a risk assessment for various diseases based on the presence of multiple genes that each contribute small effects. Therefore, if we see diseases with a shared genetic basis, it suggests there is an overlap in the polygenic profile, leading to increased polygenic risk. However, the exact risk would still depend on the combination of all genetic variants and their potential interaction with environmental factors for each particular individual concerned.