Threshold effect

In particle physics, the term threshold effect usually refers to small corrections to rough calculations based on the renormalization group that arise from the detailed behavior near the scale where new physics takes place. In the context of renormalization group, we often "integrate out" modes of quantum fields with frequencies exceeding a certain energy scale (cutoff). If the cutoff is very close to the energy scale that we want to study, the threshold effects become important and contribute small terms to formulae such as those for the beta functions.

A Threshold effect is also found in genetics whereby an organism has to acquire a certain amount of polygenes for a trait in order to produce a sufficient amount of a particular chemical to overcome a threshold. I.e., in hamsters, there are two main types of allele oconcerning the number of toes of an individual, with each loci enabling either a toe-increasing or toe-decreasing allele. 0-4 toe increasing allles gives three toes and 5-8 toe increasing alleles gives four toes, with the extra toes being produced after a sufficient amount of a certain chemical has been produced.