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Glossary of Forest Genetics Terms

This glossary of forest genetics and silviculture terms draws on a glossary by Dr. W. J. Libby for the Inland Empire Tree Improvement Co-operative (permission granted for use on this Web site) and work by the B.C. Forest Genetics Council and its cooperators.

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ACCLIMATION: The process of increasing a plant's hardiness to outdoor conditions. See hardening off.

ADDITIVE GENE ACTION: Gene products combine to produce variation in a trait in a simple linear way. See additive genetic variation.

ADDITIVE GENETIC VARIATION: The proportion of genetic variation that responds to natural selection, mass selection, or pick-the-winner selection. This is the basis of a parent's breeding value, or general-combining-ability (GCA).

ADVENTITIOUS: Meristems developing into buds, shoots or roots in places not directly associated with apical meristems or out of the normal phyllotactic pattern of the plant.

ALLELES: Alternative states of a gene. Alternative forms of a gene (at a given locus), differing in DNA sequence and usually recognized by phenotypic effects.

ALLOPATRIC: Separated. Allopatric populations do not freely exchange genes.

ANEMOPHILOUS: Wind pollinated.

ARCHIVES: For genetic conservation: Ex-situ collections of germplasm.

ARTIFICIAL SEED: Analog to true (zygotic) seed; composed of a somatic embryo encapsulated in a matrix that protects, feeds and regulates it.

ASSORTATIVE MATING: Individuals similar (positive assortative mating) or dissimilar (negative) to each other are more likely to mate (or to be mated) than if mates were chosen at random.

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BASE POPULATION: The set of trees from which selections will be taken to form advanced-generation breeding and/or production populations.

BIOREACTOR: A vessel for modest-to-large-scale liquid suspension culture of cells, in which conditions are optimized for high production levels.

BIOTYPE: Two biotypes are the two sets of phenotypes that develop in two clones.

BREEDING ORCHARD: An orchard where (usually) control-pollinations are made to produce the next generation. Many more parents are usually maintained in a breeding-orchard than in a seed-orchard.

BREEDING POPULATION: A group of selected parents that are intercrossed to form a population for the next cycle of selection. See production population and multilines.

BREEDING VALUE: The narrow-sense heritable departure of a parent's progeny-test data from the average of its population (either for one trait, or for an index of traits).

BROAD-SENSE HERITABILITY: The ratio of total genetic variance to phenotypic variance. Used to estimate the degree of genetic control of a trait in a population. Useful for predicting response to clonal selection.

BUDDING: A specialized form of grafting, in which a scion bud and adjacent cambial tissue is slipped below the bark of the stock.

BULKING UP: See vegetative multiplication.

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CALLUS: Unorganized tissue, often initiating at the cut end of a cutting or explant.

C-EFFECTS: Effects in common that are not due to genetic covariation. These may include maternal effects, a non-random common environment, or a common physiological condition of donor tissue used for cloning.

CELL LINE: A culture or cultures that arise from an individual explant. See clone.

CHIMERA: An organism composed of genetically different tissues occurring adjacent to each other.

CHRONOGENES: Genes that are activated (read) in a specific sequence.

CHRONOLOGICAL AGE: Years since germination of the ortet. Contrast to maturation state, which may vary with location in the tree as well as with ramet history.

CLEAVAGE POLYEMBRYONY: Development of multiple (genetically identical) embryos by division and separation of embryonic cells from a single zygote. See simple polyembryony.

CLONAL REPLICATION: A tool of genetic testing in which a given genotype is replicated across environments in time and space. See genetic replication.

CLONE: (a) A group of vegetatively-propagated organisms consisting of an ortet and its ramets. (b) A cell line of single-cell origin. (c) A gene or piece of DNA replicated (usually) in a host bacterium. All imply genetically (nearly) identical material, and reproduction by mitotic division.

COANCESTRY: Relatedness, which would result in inbreeding if the genotypes concerned mated and produced offspring.

CODOMINANT: The products of both genes at a locus are expressed, often nearly equally. Isozymes provide an example of codominant expression.

COMBINED TESTING: Clonal and family testing are combined in a single test, or may be carried out in parallel. See multiple-stage testing and sequential testing.

COMMERCIALIZATION: The transition from research to routine operational application (of a technology).

COMPETENCE: A developmental term referring to a cell's (or tissue's) ability to produce certain structures, organs, or even entire organisms.

COPPICE: New shoots from the stump or roots. To coppice is to cut the main stem at the base or to injure the roots in order to utilize coppicing for regeneration.

CRYOPRESERVATION: Storage of cells, tissues, seeds etc. at temperature of liquid nitrogen (-196ºC).

CULTIVAR: A 'cultivated variety', given a non-Latin name and designated by 'cv'. Any clone, race or product of breeding deemed worthy of a separate name.

CULTURE MEDIUM: Nutritive medium for the growth of tissue cultures.

CUTTING: A shoot, twig or other plant part removed from the donor plant, usually for the purpose of inducing roots to produce a steckling.

CYCLOPHYSIS: The maturation of apical meristems may lead to differences in performance among vegetative propagules taken at different times from members of the same clone or even from the same donor plant. See periphysis, topophysis.

CYTOKININS: A class of plant growth regulators involved in cell division, and often effective in shoot organogenesis.

CYTOSINE: One of the four bases that provide information in DNA, often methylated.

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DEDIFFERENTIATION: Reversion of differentiated cells or nuclei to non-differentiated (often meristematic) cells or nuclei.

DEMOGRAPHIC: Relating to density, age, and distribution of individuals in a population.

DEPLOYMENT: The physical movement of clones or other genetic units from one site (usually a nursery) to another (usually plantations), including their locational configuration on the recipient site.

DEVELOPMENTAL HOMEOSTASIS: Canalization. The degree to which some "normal" phenotype is produced in spite of variation in the environment, often the result of control systems that cushion some elements of the internal environment from the impacts of fluctuations in the external environment.

DIALLEL: A mating design that uses each parent as both a male and a female, crossed to all other parents reciprocally and including selfs. A 5-parent (5x5) diallel requires 25 matings.

DNA TRANSFORMATION: The uptake and expression of foreign DNA in a living cell. Originally defined as an inherited alteration of the phenotype of the transformed cell, see stable and transient.

DOMINANCE GENETIC VARIANCE: The component of non-additive genetic variance that is due to within-locus dominance deviations. Often used as shorthand for the portion of non-additive genetic variance estimated by full-sib/half-sib mating designs.

DOMINANCE: An intralocus interaction in which the average value of the heterozygote is not exactly intermediate between the average values of the two homozygotes.

DYSGENIC: Causing a reduction of desirable genetic qualities in natural or production populations.

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EFFECTIVE POPULATION SIZE: An adjustment of the census population number based on the distribution of reproductive success. Effective population size (Ne) will be much less than census number (Nc) if there are large differences in reproductive success. Ne equals Nc if all parents contribute equally.

ELECTROPHORESIS: A technique that allows separation of proteins and other large molecules based on their size, configuration and charge.

ELECTROPORATION: A process by which an electrical impulse is used to create transient pores in cellular membranes, thereby increasing the efficiency of uptake of DNA from solution.

ELITE TREE: A tree verified as superior or desirable by appropriate testing.

EMBLING: Somatic seedling. A propagule of somatic-embryo origin that is past the intensive-care stage of early nursery care, and can be or has been planted in normal field conditions. See steckling, plantling for parallel terminology.

EMBRYO CONVERSION: The transitionary process of embryo-to-plant development. May involve conversion from axenic to infectious environment. See hardening off.

EMBRYO MATURATION: A late phase of embryo development, leading to dormancy and germination competence.

EMBRYOGENESIS: Process by which an embryo initiates and develops from a zygote or, asexually, from a somatic cell or group of cells.

EMBRYOID: Embryo-like structure produced by somatic cells in vitro; also, adventitious embryo developing in vitro, in this latter sense = somatic embryo.

ENDONUCLEASE: A class of enzymes that cut the DNA double helix at specific 4-to-8 nucleotide sequences. See Restriction fragment length polymorphisms.

EPICORMIC: Initiating from the stem, as when dormant or suppressed buds elongate and form epicormic shoots following exposure or fire.

EPIGENETIC: Interactions among developmental processes above the level of primary gene action. Epigenetic variation does not follow the rules of Mendelian inheritance, is often the result of changed gene expression and may be reversible. It may be somatically inherited, but it is not transmitted through meiosis.

EPISTASIS: An interlocus interaction in which the expression of combinations of specific genes or genotypes from different loci is not accurately predicted by a simple linear combination of their average effects.

EX SITU: Off the site; away from the natural habitat.

EXPANSION STOCK: Propagule donors that originate from foundation stock and that are used to produce large numbers of propagules for production outplantings.

EXPLANT: An organ or tissue, excised from a donor plant, that is used to initiate an in-vitro culture.

EXTIRPATION: Local extinction; loss of some but not all populations of a species.

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F1-, F2- PROGENY: Starting with a particular cross, the offspring of that cross are the first-filial or F1 progeny, and the offspring of crosses among those F1 progeny are the second-filial or F2 progeny.

FACTORIAL MATING: A mating scheme in which m males are each crossed to the same n females is a mxn factorial. For example, if 2 trees designated male are crossed to each of 3 designated female, that is a 2x3 factorial with 6 total crosses.

FAMILY: The term "family" refers to a group of seedlings for which one or both parents are known. When only the female parent is known, it is called a "half-sib" family; when both parents are known, it is a "full-sib" family.

FAMILY FORESTRY: Tested open-pollinated, polycross or full-sib families are deployed as single families or as prescribed family mixtures.

FAMILY HEDGES: Hedges used to donate cuttings, in which sibs from the same full-sib, polycross or open-pollinated family are mixed, and their cuttings are bulked. Used for vegetative multiplication at the family level.

FARM-FIELD TEST: A test done at close spacing under near-ideal conditions, usually for the purpose of early culling.

FASTIGIATE: Having a narrow crown with ascending branches.

FECUNDITY: A measure of reproductive productivity (often restricted to female gametes, or eggs).

FITNESS: A measure of relative reproductive success. The only trait selected by natural selection.

FOUNDATION STOCK: The ultimate source of material for the clone. Often the ortet and double-labeled primary ramets. See basic material, expansion stock.

FULL-SIB PROGENY: The offspring resulting from a cross of two unrelated parents.

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GAMETOCLONAL VARIATION: Heritable variation arising in tissue-culture of gametic origin.

GAMETOPHYTE: In organisms such as trees that alternate haploid (n) and diploid (2n) phases or generations, a gametophyte is the haploid (n) gamete-producing phase or generation.

GCA: General combining ability. See additive genetic variation.

GENE AMPLIFICATION: The selective synthesis of DNA that results in multiple copies of a gene, for example the synthesis of many copies of ribosomal-RNA genes as a means of enhancing protein synthesis.

GENE MAP: A "map" of an organism’s genome, identifying and locating all its DNA sequences (genes).

GENET: The set of all modules derived from a single zygote.

GENETIC ARCHITECTURE: The distribution of genetic variation in a species, usually described hierarchically as variation at the regional, local, family and individual levels, and also relating to proportions of additive and non-additive inheritance.

GENETIC CLASS A: Seed and vegetative material derived from orchards and production facilities. Generally, seed and vegetative lots registered as Class A have a Genetic Worth greater than ‘zero’.

GENETIC CLASS B+: Seed and vegetative material derived from natural stands and identified as superior provenances. Generally, seed and vegetative lots registered as Class B+ have a Genetic Worth greater than ‘zero’.

GENETIC CLASS B: Seed and vegetative material derived from natural stands. Seed and vegetative lots registered as Class B are not assigned a Genetic Worth.

GENETIC CHIMAERA: A genetic mosaic; a tree composed of tissues of two or more genotypes. May arise as a result of somatic mutation or somatic crossing-over.

GENETIC ENGINEERING: Inserting, suppressing, or removing genetic material from a tree.

GENETIC ENTRIES: Refers to the units of test or selection, i.e., individuals, clones, families, provenances, or species.

GENETIC GAIN: The average (heritable) change from one generation to the next as a result of selection.

GENETIC MARKERS: Similar sequences of DNA that occur within certain tree families or that are associated with certain traits.

GENETIC REPLICATION: (a) A copying or transmission of DNA. (b) A tool of genetic testing in which genetic entries are replicated across environments. Provides information about the average values of the genes contained in each genetic entry, with the confounding effects of environment being estimable.

GENETIC WORTH (GW): A measure of the genetic quality of a seed or vegetative lot over wild stand material, measured for a specific trait (i.e., growth, wood density, pest resistance).

GENETICALLY MODIFIED ORGANISM (GMO): Organisms that result from the introduction, removal, or suppression of genes using DNA manipulation technology.

GENOME: All the genes of a living organism.

GENOMICS: The activity of determining the DNA sequences of genes, what they do, and how they affect cell and organism function.

GERM LINE: Cells whose cell descendents eventually undergo meiosis and produce gametes.

GERMPLASM: Genetic material. See reproductive material.

GRAFT INCOMPATIBILITY: A destructive interaction between tissues of the stock and scion, often resulting in starvation and death of the rootstock. See grafting.

GRAFTING: A form of cloning in which a bud or twig (called a scion) of the clone is inserted into a slit on a rooted and established stock plant, which may or may not be clonal. Thus, only the scion portion of a graft is usually clonal.

GxE INTERACTION: Generally: the relative magnitudes of differences in performance of a set of clones (or of other genetic entries) is different in different places or years. Narrowly: the rankings of a set of such genetic entries are different in different places or years.

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HALF-SIB PROGENIES: The offspring resulting from a cross of one parent to many other parents, each unrelated to each other or to the common parent. Usually produced in designs such as diallels or factorials. See full-sib progenies.

HARDENING OFF: By exposing propagules to increasingly harsh environmental conditions, they are weaned from the abnormally favorable conditions of the nursery, greenhouse, or culture room, and become ready for field planting.

HEDGE-ORCHARD: An orchard of hedged plants that produces cuttings or other tissue for vegetative propagation. See hedging.

HEDGING: The repeated clipping of an ortet and/or some of its ramets to produce a low hedged plant. The purposes of this procedure are to slow or halt maturation of the plant, and to control its size and shape for efficient operation.

HERITABILITY: Strictly, the ratio of genetic variance to phenotypic variance. See also narrow-sense heritability and broad-sense heritability.

HERMAPHRODITE: Bisexual; more narrowly, a plant with male and female organs in the same floral structure.

HETEROSIS: The average of the progeny is better than the average of the parents. Sometimes called hybrid vigor.

HETEROZYGOSITY: See homozygosity.

HOMOZYGOSITY: When both alleles at a locus are identical, aa or AA, the locus is homozygous. When there is one of each, Aa, it is heterozygous.

HYBRIDIZATION: Interspecific: a cross between species. Intraspecific: a cross between populations within a species, or even between individuals of contrasting genotype within a population. Introgressive: the moving of genes from one species or population to another by repeated backcrosses.

IDEOTYPE: An idealized multitrait characterization; for example, a crown that is long, narrow and dense with high branch angles.

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IN SITU: On site; within the natural habitat.

IN VITRO: "In glass"; in aseptic culture under laboratory conditions. See in vivo.

IN VIVO: Grown in natural conditions (in the field, greenhouse, etc). See in vitro.

INBREEDING COEFFICIENT: A measure of inbreeding, F, from 0.0 (the base population) to 1.0 (fully homozygous). A negative F indicates outcrossing and greater heterozygosity than in the base population.

INBREEDING: A reduction in average heterozygosity resulting from a mating between relatives.

INDETERMINATE GROWTH: Organs develop as soon as they are produced from the apical meristem, compared to determinate growth where organs are preformed in a bud and don't expand until the bud resumes growth.

ISOZYMES: Enzymes having similar structure, catalyzing the same reaction and (strictly) produced at different loci. Loosely, they may be produced by alleles (strictly, allozymes).

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KEYSTONE ECOLOGICAL ROLE: Situation in which the natural presence of a species is central to the viability of many other organisms.

KILOBASES: On a DNA or RNA strand, units of 1,000 bases.

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LEAF-AREA INDEX: A dimensionless parameter expressing the area of leaf surface over unit area of ground.

LOCUS: Plural loci. The gene, or the physical location of the gene within the DNA strand or chromosome. See alleles.

LUCIFERASES: Enzymes that produce light as a byproduct of their reaction. Used as genetic markers, and as a possible genetic engineering project for Christmas trees that glow in the dark.

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MARKER GENE: A (selectable or unselectable) gene used to indicate the presence of foreign DNA, or to locate or identify a region of a chromosome, by its presence.

MATERNAL EFFECTS: A special case of 'c-effects' due to a common maternal environment. Frequently associated with the nutrition that is provided by the mother to the embryos prior to their germination and independence.

MATURATION: A sometimes abrupt (heteroblastic) or, more common, unevenly gradual (homoblastic) process of orderly development from embryonic through juvenile and adolescent to mature.

MATURATIONAL GRADIENT: In trees, maturation is often most advanced in the upper parts of a tree and least advanced near the base of the bole, with intermediate conditions in between.

MEGAGAMETOPHYTE: In a conifer, the haploid cells and tissues developing from the maternal gamete, with nutritive and other functions for the contained zygote.

MEIOSIS: A special cell division that results in a reduction of somatic-cell chromosome number (2n) to gamete chromosome number (n).

MENDELIAN RULES OF INHERITANCE: A binary (for diploids) system of rules based on segregation of alleles at meiosis and recombination at fertilization.

MERISTEM: An undifferentiated plant tissue, often with rapidly dividing cells, from which new tissues or organs arise.

METHYLATION: Addition of a CH3 group. For DNA, the methyl group is usually added to a cytosine residue.

MICROCALORIMETRY: The (computerized) detection of small amounts of heat produced by live tissue.

MICROINJECTION: Direct physical injection into individual cells, particularly for DNA transfer.

MICROPROJECTILE BOMBARDMENT: A method for direct physical transfer of DNA into a recipient cell at high velocity by means of a blank cartridge or other blast of gas or charged water.

MICROPROPAGATION: The in-vitro vegetative propagation of plants, often called plantlets, micropropagules, or somatic embryos.

MICROSPOROGENESIS: The development of pollen.

MITIGATION: Restoration actions taken on a species or population specifically to compensate for previous or (on other sites) planned destructive actions.

MONOCLONAL BLOCKS: A deployment option for clones (or, similarly for families in monofamily blocks) in which each clone (family) is established in a pure block. Diversity may be maintained by a mosaic of blocks of different genetic entries.

MORPHOGENESIS: The process of differentiation of cells into different tissues or structures.

MULTICLONAL MIXTURE: A mixture of clones in (usually) equal proportions for use in forest plantations. See multiclonal variety

MULTICLONAL VARIETY: A cultivar (variety) composed of several compatible clones.

MULTI-GENE FAMILY: Loci with identical or similar primary products and function, probably evolved by duplication and then, in some cases, some differentiation at the gene level.

MULTILINES: Sublines of the general breeding population purposefully selected for different sets of traits or deployment destinations.


MULTIPLE-STAGE TESTING: See sequential testing, combined testing. May also include separate tests for different purposes, such as resistance to different pests and stresses.

MUTATION: A heritable genetic change. Somatic: occurring in a somatic cell and thus not necessarily passed on to sexual offspring. Germinal: occurring in the germline, and thus may be passed on to sexual offspring.

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NARROW-SENSE HERITABILITY: The ratio of additive genetic variance to phenotypic variance. Useful in predicting the response of a population to natural selection or to pick-the-winner selection. Related to breeding value.

NEUTRAL ALLELES: Alleles subject to no (or very weak) selection pressure, and thus useful as evolutionary clocks, for mating-system estimation, and similar selection-free chores.

NON-ADDITIVE GENE EFFECTS: See dominance, epistasis.

NON-ADDITIVE GENETIC VARIATION: The proportion of genetic variation that doesn't respond to simple mass selection, and that causes specific pairwise crosses to depart from performance values predicted by the breeding values of the parents.

NUCLEOTIDE: A building block of DNA or RNA, consisting of a phosphate group, a sugar, and a purine or pyrimidine base.

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ONTOGENETIC AGING: Aging or maturation that occurs in a normal sequence.

ONTOGENETIC: Normal sequence of development; going through the usual stages of a life cycle.

OPEN-POLLINATED PROGENY: Progeny from a mating that is not controlled. A mixture of related and unrelated pollen is delivered by wind, or in some cases by insects etc. The o-p family is typically a mixture of full-sibs, half-sibs, and selfs, or, in a natural stand, of such relatives with various degrees of inbreeding.

ORGANELLE: A body with specific structure and likely function in the cytoplasm of a cell.

ORGANOGENESIS: The process involving differentiation of organs from cells and tissues.

ORGANOGENIC CAPACITY: Competence to form or give rise to an organ. See competence.

ORTET: The initial individual (usually from a zygotic embryo) that is vegetatively propagated to produce a clone. See ramet.

ORTHOTROPIC: Growing vertically, usually with radial symmetry. Contrast to plagiotropic.

OVERDOMINANCE: A special case of dominance in which the heterozygote is, on average, outside the range of the averages of the two homozygotes.

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PEDIGREE: A record of parentage, often including data on performance of the parents and of other relatives.

PERIPHYSIS: Effects of the environment in pre-conditioning tissue, which may lead to differences in performance of vegetative propagules taken from different members of the same clone or from different parts of the same donor plant. See cyclophysis, topophysis.

PHASE CHANGE: The developmental change from one maturation state to the next.

PHASIC DEVELOPMENT: The orderly development from one normal phase to the next. See phase change.

PHENOTYPE: The observed expression of a trait in an individual that is the result of a developmental interaction of the individual's genotype and its operational environment.

PHENOTYPIC PLASTICITY: The degree to which different phenotypes are produced by the same genotype (clone) in different environments.

PHOTOPERIOD: Day length. Used to describe the relationship between phenology and episodes of light.

PHYSIOLOGICALLY MATURE: Exhibiting "mature plant" traits; may or may not be associated with high chronological age.

PHYTOHORMONES: A broad class of naturally occurring chemicals, effective at very low concentrations for regulating plant growth and development. See auxin, cytokinin.

PLAGIOTROPIC: A branchlike growth form of an independent plant, usually at an angle other than vertical and often bilaterally metrical.

PLAGIOTROPISM: A tendency for a propagule to grow at an angle and like a branch, in contrast to vertical, or orthotropic, growth.

PLANTLET: Broadly, a plant produced in-vitro. Narrowly, the intensive-care stage of a plant produced in tissue-culture. See plantling.

PLANTLING: A propagule of tissue-culture origin that is past the intensive-care stage of early nursery care, and can be or has been planted in normal field conditions. See embling, steckling, hardening off.

PLUS-TREE: A tree or genotype selected on the basis of its outstanding single-copy performance, but not yet clonally tested or progeny tested.

POLYCULTURE: The intimate mixture of several species; in agroforestry, these include animal and/or crop components in addition to one or more tree species or cultivars.

POLYGENIC: Said of a trait controlled by several-to-many loci, each having relatively small effect on the expression of the trait.

POLYMERASE CHAIN REACTION (PCR): Specific amplification of DNA sequences by preferential replication of the sequence between two sites defined by certain DNA polymerase primers.

POLYMIX CROSSES: Polycross. A mating scheme in which several (usually > 10) pollens (usually unrelated to each other) are mixed and crossed as that mix to a series of females that are (usually) unrelated to any of the males.

POLYMORPHISM: Occurring in more than one form in a population, usually with the rarer morph at or above some minimum frequency (say 1%).

PRECOCIOUS: In the reproductive sense, to predictably exhibit reproductive competence at an early age or small size.

PRIMER: An initiator for polymerase reactions on DNA, for example oligonucleotides paired to a single-stranded region and having an unblocked 3-prime hydroxyl group to which nucleotides can be added.

PRIMORDIUM: A group of cells that gives rise to an organ, with some commitment and differentiation begun.

PROBE: A small piece of radiolabeled nucleic acid used for detection of its complementary sequence by nucleic-acid hybridization.

PRODUCTION CLONES: Those clones maintained in large enough stoolbeds, hedges, cultures, etc. to supply large numbers (say 20,000) of cuttings per year for planting. See production population.

PRODUCTION POPULATION: Usually a highly selected subset of the breeding-population parents or clones that is propagated sexually or vegetatively for operational reforestation. See multilines, production clones.

PROGENIC: Causing improvement of genetic qualities in natural or production populations of a species. Similar to eugenic.

PROGENY TEST: Generally a common-garden test in which the breeding values of parents are evaluated and ranked on the basis of the performance of their offspring. See progeny trial, provenance test.

PROGENY TESTED: Selected parents which have been evaluated based on the performance of their offspring in scientifically designed progeny trials.

PROGENY TRIAL: A trial in which pedigreed progeny are used either to backward-select among the parents (a progeny test) or to forward-select among the offspring (not a progeny test).

PROMOTER: The region of DNA at the upstream (5-prime) end of a gene or operon that serves as the initiation site for transcription. Promoters can be complex, containing several sequences that regulate level of expression as well as the temporal and spatial expression of the gene.

PROTOPLAST: A plant cell without a cell wall; it may be produced by enzymatically removing the cell wall.

PROVENANCE TEST: A common-garden test in which population samples from stands of known evolutionary origins are grown together in fair comparisons in one or more locations.

PROVENANCE: The geographic origin of a population. Mostly (but not always in European usage) the ultimate natural origin, implying where the population evolved prior to human intervention.

PROVENANCE TESTED: Seed sources that have been tested in provenance trials where population samples from stands of known evolutionary origins are grown together in fair comparisons in one or more locations.

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QUIESCENT CENTRE: Within the rapidly dividing group of cells in the root meristem is a small group of cells that rarely divide, and these are carried passively within the rest of the meristem. It is currently controversial whether such exists in the shoot apical meristem.

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RAMET: All vegetative propagules of an ortet are ramets. A clone is composed of the ortet and its ramets.

RAMICORN: A large high-angled branch, often resulting from one member of a fork being partly suppressed by the more dominant member.

RANDOM MATING: In the ideal case, each individual in the population has the same probability of mating with every other individual. In practice, no selection influences the matings that occur.

RECIPROCAL RECURRENT SELECTION: A complicated breeding scheme in which selection within each of two independent lines is based on progeny tests of crosses between the lines. It is meant to select for both additive and non-additive genetic variation.

RECOMBINANTS: Individuals having new combinations of the genes (alleles) of the parent(s), the term often used when the genes are linked.

RECURRENT BREEDING/IMPROVEMENT: A process aimed at achieving long-term improvement in a set of value traits through selection, breeding and testing in repeated cycles (generations).

REGENERATION: The reestablishment of a forest; in tissue culture, the production of organs, embryos or whole plants, usually as a morphogenic response to stimulus.

REINVIGORATION: Reinvigoration occurs when plants or organs improve their external and internal environment, particularly their nutritional and water status, sometimes producing juvenile-appearing traits. See rejuvenation.

REJUVENATION: A change in a tissue or an organism from a more mature state to a more juvenile one.

REPORTER GENE: A marker gene used in transformation studies to indicate the presence of foreign DNA.

REPRODUCTIVE MATERIAL: All material produced by sexual and asexual means used for plant production. See germplasm.

RESTORATION: Actions taken to promote genetic or ecologic recovery of a population or species following natural or artificial destruction or impoverishment of the population or species.

RESTRICTION FRAGMENT LENGTH POLYMORPHISM (RFLP): Variation in the lengths of DNA fragments resulting from predictable cutting by restriction enzymes, which cleave the DNA double helix at specific nucleotide sequences.

RIBOSOME: The small organelle that is the site of protein synthesis.

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SCA: Specific combining ability. Can refer to the degree to which the average performance of a specific (usually full-sib) family departs from the average of its parental breeding values; sometimes used in a similar sense to note the departure of an individual clone from the performance of its sibs; sometimes used to note the degree of non-additive genetic variation in a population.

SCALE-UP: The transition from research-scale to operational-scale application of a technology.

SCION: The (usually desired) clonal plant part, often a twig, that is grafted onto the root-bearing part of another plant. See stock.

SEED ORCHARD: An orchard consisting of clones or seedlings from selected trees, isolated to prevent or reduce pollination from outside sources, and cultured for early and abundant production of seeds for reforestation.

SEED SOURCE: The geographic source of a seed. If a native stand, equivalent to provenance.

SEED SOURCE TESTED: Seed sources tested in scientifically designed provenance (seed source) trials, typically across a series of test sites.

SEED STAND: A plantation or natural stand designated for repeated collection of seeds for reforestation purposes.

SEEDLOT: A quantity of cones or seeds having uniformity of species, source, quality, and year of collection.

SELECT SEED: Seed and vegetative material having a level of gain greater than zero for some trait of interest. Generally, lots registered as select are assigned a Genetic Worth.

SELECTABLE MARKER: May be used in marker-assisted selection, or to select a transformed genotype from a mixture of transformed and nontransformed cells. RFLPs, antibiotic-resistant and herbicide-resistant sequences or genes are examples, the latter resulting in killing cells lacking the marker.

SELECTION INTENSITY: (This term has two conflicting meanings, and can cause confusion.) (a) The standardized selection differential between the average of the selected population and the average of the population selected from. (b) The percentage of individuals selected from a candidate population.

SELFING: Self-pollination, when a female cone is pollinated with pollen from the same tree or clone.

SENESCENCE: An advanced state of aging, often associated with a sharply decreased ability to repair damage.

SEQUENTIAL TESTING: A testing approach in which large numbers of genetic entries are tested in few replications in the early stages (say screening and then candidacy testing) and progressively fewer entries are then tested in more replications or in larger plots (say performance or compatibility testing). See combined testing, multiple-stage testing.

SERIAL PROPAGATION: The ortet donates cuttings or tissue that become primary ramets, some of which in turn later donate cuttings or tissue that become secondary ramets, etc.

SEX RATIO: Generally, the ratio of males to females at some point in development. On a monoecious tree, the ratio of male to female strobili or flowers.

SIMPLE POLYEMBRYONY: The creation of (for example) 3/4-sibs by the fertilization of genetically identical eggs within a single gametophyte by genetically non-identical pollen from a single male. See cleavage polyembryony.

SOMACLONAL VARIATION: Variation arising in tissue-culture of somatic tissue, often at unusually high rates due to higher rates of gene mutation, transpositions, and various chromosome abnormalities. See gametoclonal variation.

SOMATIC CROSSING-OVER: An exchange of genetic material between homologous chromosomes in somatic cells, i.e., that is not associated with their pairing at meiosis.

SOMATIC EMBRYOGENESIS: A process by which somatic cells (non-reproductive seed tissue) are differentiated into somatic embryos.


SOURCE: The geographic source (provenance) of cones, seeds, and vegetative material, including the latitude, longitude, and elevation of the source, or the name and licence number of the seed orchard or cutting orchard.

SPOROPHYTE: The diploid (2n) spore-producing phase or generation. See gametophyte.

SRIC: Short-rotation intensive culture.

STABILITY: Stable clonal mixtures or ecosystems are less likely to respond dramatically to physical and biotic perturbations than unstable ones. Re clones: rankings of stable clones are fairly constant with modest changes in environment.

STABLE TRANSFORMATION: As distinguished from transient expression of foreign DNA, a stable transformation is foreign DNA incorporated into the host genome (usually a chromosome) and it is inherited.

STECKLING: A rooted cutting that is sufficiently developed so that it can be or has been planted in the field. See embling, plantling for parallel terminology.

STOCK: For grafting, the rootstock on which the scion is grafted.

STOCKTYPE: The kind of propagule sent to the field, such as container-grown or bare-root; seedling, steckling or plantling; etc.

SUBLINES: A more-or-less arbitrary separation of lines within a breeding population; breeding crosses are made within lines and production crosses between lines, resulting in no inbreeding in the production stock.

SUPERIOR PROVENANCE: Provenances (seed sources) derived from natural stands that have been identified as having superior traits (e.g., growth performance) over that of local natural stand seed sources as shown through an extensive series of provenance trials. Typically referred to as B+.

SUSPENSION CULTURE: The culture of plant cells in liquid medium, where cells or clumps of cells are aerated and maintained in a dispersed state by gyration of the vessel.

SUSPENSOR CELLS: Cells that develop very early in ontogeny from the base of the embryo, which elongate to push the embryo into the megagametophyte or endosperm, and which are often embryogenic in culture.

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TECHNOLOGY DEVELOPMENT: The process of developing procedures through trials and experiments. See technology transfer.

TECHNOLOGY TRANSFER: The stage in development of a technology or process in which operational personnel learn about the technology, commit to it, and develop procedures for operational-scale application.

TISSUE CULTURE: A general term for aseptic cell, tissue, organ and protoplast culture. Strictly, aseptic culture of callus tissue.

TOPOPHYSIS: Differences in maturation or developmental potential among apical meristems of different branch hierarchical order may result in differences in performance among vegetative propagules taken from different parts of the same donor plant. See cyclophysis, periphysis.

TOPWORKING: Grafting of scions into the tops of trees, usually in the hope of inducing flowering by the scions.

TOTIPOTENCY: Said of a nucleus, cell or tissue that has the capacity to develop into a complete organism. See competence.

TRANSCRIPTION: The enzyme-mediated process of transcribing the information in a DNA strand into a complementary RNA strand.

TRANSGENIC PLANT: A plant containing DNA inserted by some form of genetic engineer, usually by a transformation event in culture followed by regeneration and recovery of a plant.

TRANSIENT EXPRESSION: Foreign DNA in a cell with expression that decays with time and is not inherited.

TRANSLATION: The process by which information in an mRNA strand creates the sequence of amino acids during polypeptide (protein) synthesis. See ribosome.

TRUE-TO-TYPE: Individuals having essentially the same phenotype as the donor plant, cultivar or clone.

TRUNCATION SELECTION: All members of a candidate population equal to or greater than some minimum value in a trait or index are selected, and no members below that value are included in the selected set.

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UNSELECTABLE MARKER: Markers such as "gus" or "lux" that are (usually histologically) detectable but can not be efficiently used to sort transformed from untransformed cells.

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VALUE FUNCTION: The goal of an organization or program expressed in terms of a set of value traits; the relationships among a set of traits expressed in terms of the defined values of those traits.

VALUE TRAITS: The characteristics that are important contributors to the value of a genetic improvement program.

VARIANCE: A statistical measure of variation with the useful property of having additive components, for example genetic and environmental components of total phenotypic variation.

VARIETY: See cultivar.

VECTOR: A carrier of a disease, or, for genetic engineering, of foreign DNA.

VEGETATIVE LOT: A quantity of vegetative material or vegetative propagules having a uniformity of species, source, and year of collection.

VEGETATIVE MATERIAL: Material produced asexually. Most vegetative material used in B.C.’s reforestation program is from hedges and stoolbeds for species with a limited supply of high quality seed (e.g., yellow-cedar) or for which vegetative propagation is preferred (e.g., hybrid and native poplars).

VEGETATIVE MULTIPLICATION: When seeds of desired families or populations are in short supply, embryos or seedlings are clonally reproduced by rooting cuttings, tissue culture, grafting, or somatic embryogenesis. Clonal records are usually not kept.

VEGETATIVE PROPAGATION: Asexual propagation. See clone, cutting, embryogenesis, grafting, tissue culture.

VIRULENCE: The relative infectiousness of a microorganism that causes disease or infection.

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ZYGOTIC FORESTRY: Whether seedlings or clonal propagules, individual genotypes are not well known or characterized. Performance knowledge is at the level of family, breed or population. See vegetative multiplication.

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