Question

researchers refer to alleles that are involved in polygenic disorders as \disease risk loci\ instead of \disease determinants loci.\ make an inference: why is this distinction logical? particular alleles can increase the risk of developing a disease, but whether disease actually occurs depends on the alleles present at other genes and on the environment. diseases and other traits can only be referred to as \determined\ if they are due to the products of a single gene. polygenic traits are so difficult to study that its hard to identify the genes that determine the trait.

Explanation:

Polygeneic traits are influenced by multiple genes and environmental factors. This complexity makes it hard to isolate specific genes as in single - gene traits. For example, height is affected by many genes and nutrition. Diseases like heart disease also have multiple genetic and environmental risk factors. So, the distinction is logical because polygenic traits/disorders involve multiple genetic and environmental determinants, unlike single - gene conditions.

Answer:

Polygeneic traits are difficult to study and identify genes because they are influenced by multiple genes (not a single gene) and environmental factors. In contrast, single - gene traits are determined by the products of a single gene. For polygenic disorders (like the ones mentioned where alleles at multiple loci affect disease risk), it's not just about the presence of certain alleles (as in some single - gene - related disease associations where a specific allele might directly cause a disease). The overall risk in polygenic disorders depends on the combination of alleles at multiple loci and environmental interactions. So, referring to alleles involved in polygenic disorders as "disease risk loci" (indicating they contribute to risk) rather than "disease determinants loci" (which implies a more direct, deterministic role as in some single - gene scenarios) is logical.