- taken & adapted from Hillis et al (1996), Majerus et
al (1996) and Walker (1989)
Paralogy: Homology that arises via gene duplication.
Paraphyletic: A taxon that excludes species that share a common
ancestor with its members.
PCR: see Polymerase chain reaction.
Phenetics: Classification based on overall
similarity in as many characters as possible, usually without weighting.
Phenogram: A branching diagram that links entities by estimates
of overall similarity.
Phenotype: The observable properties of an organism, resulting
from the interaction between the organism's genotype and the environment
in which it develops.
Phylogeny: The historical relationships among entities. Differs
from a cladogram in that the branches are drawn proportional to the
amount of inferred character change.
Phylogenetic tree: A diagrammatic representation of genetic
distances between populations, species or higher taxa, the branching
of which is said to resemble a tree.
Plesiomorphy: An ancestral character state.
Polymerase chain reaction: A method of amplifying specific DNA
sequences by means of repeated rounds of primer-directed DNA synthesis.
Polymorphism: The presence of several forms of a trait, gene
or DNA sequence in a population.
Polyphyletic: A group of taxa that are derived from two or more
ancestral forms not common to all members, (opposite of monophyletic).
Pseudogene: A gene showing significant sequence homoplasy (>75%)
to a functional gene, but which has lost any normal function, often
through gaining internal stop codons.
Random genetic drift: Fluctuation in the frequencies of neutral
genes and neutral alleles in a population due to the fact that each
generation is only a sample of the one it replaces.
Ribonucleic acid: A polynucleotide consisting of a chain of
sugar and phosphate units to which are attached various nitrogenous
bases, (adenine, cytosine, guanine and uracil).
Sexual selection: Selection which promotes traits that will
increase an organism's success in mating and ensuring that its gametes
are successful in fertilisation. This is distinct from natural selection
which acts simply on traits which influence fecundity and survival.
Species: A cohesive historical lineage of ancestral-descendant
populations of organisms that maintains its identity from other such
lineages. A species comes into being at a branching event (when one
lineage becomes one or more lineages), and ceases to exist either at
a branching event (when it gives rise to new species) or when the lineage
is terminated through extinction.
Symplesiomorphy: A shared ancestral character state.
Synapomorphy: A shared derived character state that is indicative
of a phylogenetic relationship among two or more OUT's.
Unrooted tree: A phylogenetic tree that is not directed with
respect to time.
Xenology: Homology that arises via lateral gene transfer between
unrelated species (e.g., by retroviruses).