is known. Proceeding as if it is understood is enough to analyze many cases of interest. For example, if the phenotype is almost one-to-one with genotype (sickle-cell disease) or the time-scale is sufficiently short, the "constants" can be treated as such; however, there are also many situations where that assumption does not hold. References External links Stanford Encyclopedia of Philosophy entry "Wilhelm Johannsen's Genotype-Phenotype Distinction" at the Embryo Project Encyclopedia Genetics