Editing Peppered moth (section)

== Polymorphism ==
{{Further|Polymorphism (biology)}}

=== Introduction on forms ===
There are several [[melanism|melanic]] and non-melanic [[Polymorphism (biology)|morphs]] of the peppered moth. These are controlled genetically. A particular colour morph can be indicated in a standard way by following the species name in the form "morpha ''morph name''". The use of "form" in the method of ''Biston betularia'' f. ''formname'' in detailing these variations is also a widespread practice.

These forms are often accidentally elevated to subspecies status when they appear in literature. Not adding the "f." (forma) or morpha implies that the taxon is a subspecies instead of a form, as in ''Biston betularia carbonaria'' instead of ''Biston betularia'' f. ''carbonaria''. Rarely, forms have been elevated to species status, as in ''Biston carbonaria''. Either of these two circumstances might lead to the erroneous belief that [[speciation]] was involved in the observed evolution of the peppered moth. This is not the case; individuals of each morph interbreed and produce fertile offspring with individuals of all other morphs; hence there is only one peppered moth species.

By contrast, different subspecies of the same species can theoretically interbreed with one another and will produce fully fertile and healthy offspring, but in practice do not, as they live in different regions or reproduce in different seasons. Full-fledged species are either unable to produce fertile and healthy offspring, or do not recognize each other's courtship signals, or both.

European breeding experiments have shown that in ''Biston betularia betularia'', the [[allele]] for melanism producing morpha ''carbonaria'' is controlled by a single [[locus (genetics)|locus]]. The melanic allele is dominant to the non-melanic allele. This situation is, however, somewhat complicated by the presence of three other alleles that produce indistinguishable morphs of morpha ''medionigra''. These are of intermediate dominance, but this is not complete (Majerus, 1998).

=== Form names ===
In continental Europe, there are three morphs: the white morph '''''typica''''' (syn. morpha/f. ''betularia''), the dark melanistic morph '''''carbonaria''''' (syn. ''doubledayaria''), and an intermediate form '''''medionigra'''''.

In Britain, the typical white morph is known as '''''typica''''', the melanic morph is '''''carbonaria''''', and the intermediate [[phenotype]] is named '''''insularia'''''.

In North America, the melanic black morph is morpha '''''swettaria'''''. In ''Biston betularia cognataria'', the melanic allele (producing morpha ''swettaria'') is similarly dominant to the non-melanic allele. There are also some intermediate morphs. In [[Japan]], no melanic morphs have been recorded; they are all morpha ''typica''.