Principios de Taxonomia

Scientific Terms j235
the spring of the following year; these are the migratory morphs. Another subset of
the individuals of the same population in the same region remains in the breeding
area during the winter; these are the sedentary morphs.
Phenetics A formal species concept that unites all organisms into a common
species with similar traits. Phenetics is a quantitative method and is therefore
independent of subjective evaluations. It is, however, an artificial system.
Phenotype Traits of an organism, ranging from direct expression products of the
genes (as proteins) to complex body structures, behavioral features or developmental
pathways (see genotype).
Phylocode The phylocode is an attempt to replace the outdated Linnaean taxon
names with novel names. Phylocode names are names for monophyla, including
more or less branches of a cladistic tree (Figure 7.12). The phylocode aims to avoid
taxonomic ranks, such as genera, families, orders or classes, because such ranks do
not exist in nature, and they lead to the incorrect impression that taxa of equal ranks
are comparable among different animal or plant groups.
Polygeny A single trait being controlled by many coexisting genes. A contrasting
case is polypheny, in which a single gene controls several, often very different
phenotypic traits.
Polymorphism This term has almost the same meaning as multiple allelism but is
preferentially used for phenotypic traits, rather than for genes. Polymorphism is the
entirety of the differences in the phenotypic expression of a particular gene within the
individuals of a species (see multiple allelism).
Polymorphism, stable The special capacity of particular alleles to survive as
multiple variants for long evolutionary period in a species without being
eliminated by selection or genetic drift. Most newly originated alleles are either
fixed in a population relatively rapidly or they are eliminated. In the rare case of stable
polymorphism, however, the selective advantage related to the survival of the
population is not based on the quality of a single particular allele, but on the
existence of a multitude of alleles of a gene. This confers flexibility on a
population in a changing environment because different alleles of a gene with
different selective advantages are distributed among many individuals.
Population A subgroup of the organisms of a species within a delimited range of
occurrence. A population is a rather artificial kind of group formation, mainly aimed
at providing manageability for pragmatic purposes.
Postzygotic barrier The occurrence of hybrid incompatibility or hybrid dysgenesis
in the offspring produced via species crossings. In such hybrids, the cooperation of
particular genes that originate from the two different parent species, is disturbed,
resulting in a reduction of fertility or vitality.
Prezygotic barrier The occurrence of morphological, physiological or ethological
traits that prevent the formation of zygotes between two organisms. Prezygotic