Methods for determining a property that affects expression of polynucleotides are provided. A plurality of polynucleotides each encoding a polypeptide sequence is constructed. A frequency that a sequence element is used in a first polynucleotide is different than in a second polynucleotide. Each polynucleotide is expressed in an expression system to obtain an expression property value thereby constructing a dataset that contains, for each respective polynucleotide, sequence element occurrence in the respective polynucleotide and the measured expression property value of the respective polynucleotide. A model is computed that describes variation in the measured expression property values as a function of a plurality of variables and weights. From the model, a property that affects expression of polynucleotides in the expression system is determined, where the property is an effect that the frequency of occurrence of one or more sequence elements has on the expression property of polynucleotides in the expression system.