ALLELIC SERIES A series of alleles that can be present at the same locus and that produce graded phenotypes.
ALLOTETRAPLOIDY The generation of the tetraploid state by fusion of two nuclei from different species. For example, two fertilized diploid oocytes can fuse such that the newly formed single egg has two complete sets of chromosomes.
AUTOTETRAPLOIDY In contrast to allotetraploidy, both sets of chromosomes are derived from the same species. This can occur in the fertilized oocyte if the nucleus divides but the cell does not.
CLADE A lineage of organisms or alleles that comprises an ancestor and all its descendants.
CONSERVED SYNTENY (syn, same; teny, thread). Homology of gene order between two chromosomes or chromosomal segments, within or between species.
DEGENERATIVE MUTATION A sequence change that causes a loss of function of the affected sub-function or gene.
ECOTYPE A subdivision of a species that survives as a distinct population through environmental selection and reproductive isolation.
EFFECTIVE POPULATION SIZE The equivalent number of breeding adults in a population after adjusting for complicating factors, such as non-random variation in family size or stochastic fluctuation in population size.
GENETIC DRIFT The increase or decrease in allele frequencies in populations due to chance.
INDIVIDUAL RELATIVE FITNESS The capacity of the individual to survive and reproduce.
INFLORESCENCE MERISTEM An apical meristem that lies atop a shoot and that produces several, lateral flower meristems.
LENS CRYSTALLIN A protein that accumulates at high concentration in the eye and that forms the crystallin lens.
MADS BOX A highly conserved sequence motif found in a family of plant transcription factors and named after the initials of the four founder members of the family.
MERISTEM An undifferentiated cell population that resides at the growing tip of the roots or shoots of a plant.
MORPHOLINO An antisense reagent that is able to block translation to knock down gene function.
NEO-FUNCTIONALIZATION When one of two duplicate genes acquires a mutation in coding or regulatory sequences that allows the gene to take on a new and useful function.
NEURAL CREST A vertebrate-specific migratory cell type that derives from the dorsal-most aspect of the neural tube and contributes to many tissues, including the peripheral nervous system and cranium.
NON-FUNCTIONALIZATION When one of two duplicate genes acquires a mutation in coding or regulatory sequences that ultimately renders the gene non-functional.
ORGANIZER A small dorsal region of the vertebrate gastrula-stage embryo that has the remarkable capacity to organize a complete embryonic body plan. Hilde Mangold and Hans Spemann first identified the organizer in amphibian embryos using tissue transplantation.
ORTHOLOGUES Homologous genes that are related by a speciation event. For example, mouse Hoxa1 and chick HOXA1 are orthologues.
PARALOGUES Homologous genes that are related by a duplication event. For example, mouse Hoxa2 and Hoxb2 are paralogues.
PLEIOTROPY When a single gene has a role in several processes.
POLYPLOIDY A polyploid organism has more than two sets of chromosomes (two sets being the prevalent diploid state). For example, a tetraploid organism has four sets of chromosomes and an octaploid has eight sets.
PURIFYING SELECTION Selection against deleterious alleles, which will be eliminated from the population.
REDUNDANCY When two genes can fulfil an equivalent function. Because of pleiotropy, redundancy is often partial, with two genes having overlapping rather than equivalent functions.
REPLACEMENT ALLELE An allele in which a mutation causes a resulting change in amino-acid identity.
RHOMBOMERE A segment of the vertebrate hindbrain (rhombencephalon).
STAMEN The male, pollen-bearing organ of the plant.
SUB-FUNCTION Any functionally discrete, independently mutable portion of a locus. For example, a cis-regulatory element, a protein domain or an alternative splice site.
SYNONYMOUS CHANGE A nucleotide change that does not alter the amino acid that is encoded.
TELEOST A bony fish that belongs to the infraclass Teleostei (comprising more than 20,000 species), which includes nearly all the important food and game fish, and many aquarium fish.
TETRASOMY When one chromosome in the complement is represented four times in each nucleus.
