Glossary of Forest Genetics Terms

Prepared by Jack Woods, SelectSeed Ltd.

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ACCLIMATION: The processes by which plants increase their hardiness to outdoor conditions such as cold or drought. See hardening off.

ADAPTATION (Genetic): The genetic change of a population (of trees) whereby some individuals are selected relative to other individuals due to higher fitness (more successful reproduction) by the environment they are in, resulting in future generations containing more of the genes of the more fit individuals. Also see ASSISTED POPULATION MIGRATION, ASSISTED SPECIES MIGRATION, and EXOTICS.

ADAPTATION (Physiological): The physiological adjustment of an individual (tree) in response to environment.

ADAPTATION LAG: When genotypes are not optimally adapted genetically to the environment they are in due to a change in the environment (i.e. climate change). Adaptation lag can be described for species, such that a “realized NICHE”, where trees are currently present in their NATURAL RANGE, is not geographically the same as a “fundamental NICHE”, where trees could grow, but are not necessarily present due to the evolutionary ADAPTATION LAG. Adaptation lag can be similarly described for a population of trees, such that the realized niche for a population is different than the fundamental niche where the population would be best adapted genetically.

ADAPTED: Individuals (trees) that, through natural evolution or breeding and testing, are capable of growth and reproduction in a given environment. In forestry this usually refers to populations of trees that have the capability to grow, reproduce, and remain generally healthy in a given climatic environment.

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 forms of a gene (at a given locus), differing in DNA sequence and sometimes resulting in different phenotypic effects.

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

ANEMOPHILOUS: Pollinated by wind-borne pollen.

ARCHIVES: For genetic conservation: Ex-situ collections of germplasm such as seed in storage.

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

ASSISTED MIGRATION (general): Assisted migration generally refers to the movement of organisms to mitigate the negative impacts of global change to the organism. In forestry, assisted migration often refers to the establishment of forest plantations using seed sources from climates that are slightly warmer than that of the plantation. The goal is to maintain forest health and productivity by ensuring plantation trees are climatically adapted to current and future plantation climates. In forestry, the term is often used interchangeably with assisted range expansion, assisted colonization, or managed relocation. Also see ASSISTED POPULATION MIGRATION, ASSISTED SPECIES MIGRATION, and EXOTICS.

ASSISTED POPULATION MIGRATION: The human-assisted migration of genetic populations of a species to new areas that are within the species current natural range. (Also referred to as ASSISTED POPULATION EXPANSION or ASSISTED GENE FLOW).

ASSISTED SPECIES MIGRATION: is the movement of a species to new areas that are outside the species natural range. Specifically, this involves an expansion into geographic areas the species’ climate envelope is moving into , and a contraction from areas the species envelope is moving from . Differs from EXOTICS in the degree of geographic movement.

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 (orchard) populations.

BIODIVERSITY: The variety and variability among living organisms and the ecosystems of which they are part. Biodiversity has three levels or components – ecosystem diversity, species diversity and genetic diversity.

BIOGEOGRAPHY: The study of the distribution of organisms over the earth and of the principles, such as climate, that govern their distribution.

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 different clones.

BREEDING: The science and art of changing the genetic constitution of a population of plants or animals through controlled mating of individuals selected for trait(s) of interest.

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 parent trees that are intercrossed to form a population for the next cycle of selection. See PRODUCTION POPULATION and MULTI-LINES.

BREEDING VALUE: The narrow-sense heritable difference between a parent’s progeny-test data and the average of its population (either for one trait, or for an index of traits). In BC, the breeding value of a parent tree is quantified as the heritable difference in the performance of the trees offspring relative to offspring from non-selected local natural populations grown under the same conditions.

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 inserted below the bark of the rootstock and secured there until the bud and the rootstock grow together.


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

C-EFFECTS: Effects–in-common between individuals 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 from seed. Contrast to maturation state, which may vary with location in the tree as well as with tree history.

CLIMATE BC AND CLIMATE WNA: Models that extrapolate historic climate data across geographic areas, integrate global circulation model (GCM) data, project historic climate data based on GLOBAL CIRCULATION MODEL predictions, and present data is useable forms in support of a broad range of uses. ClimateBC and ClimateWNA were developed at the University of BC by T. Wang and Andreas Hamann and continue to be developed and maintained by T. Wang.

CLIMATE-BASED SEED TRANSFER (forestry context): A system for managing the transfer of reproductive material (seed, seedling, etc.) that is based on the matching of genetic populations with the climatic areas to which they are optimally adapted for health and long-term growth. A climate-based seed transfer system may or may not be combined with ASSISTED MIGRATION.

CLINAL or CLINAL VARIATION: The continuous gradient of a trait that is assumed to be genetically controlled and linked with the environment of the geographic area in which the species exists. With clinal variation the genetic differences between natural populations transition without large changes over short distances. For example, the frost hardiness of tree populations increases from lower to higher elevations.

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 between individuals due to a common ancestor(s) that 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.

CONE INDUCTION: Inducing a conifer tree to produce female and male strobili through methods that alter the hormone state within the tree (i.e. stem injection of hormones such as gibberellic acid) or stress the tree (i.e. stem girdling by removing a strip of bark).

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.

CRISPR: Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR) that is used to modify DNA sequences for the purpose of editing genomes or genetic engineering. It is an RNA-guided gene-editing method that is derived from Streptococcus pyogenes and uses an endonuclease (Cas9) and a synthetic guide RNA to introduce a double strand break at a specific location within a genome.

CRYOPRESERVATION: Storage of cells, tissues, seeds etc. at the 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.

DEPLOYMENT: The physical movement of clones or other genetic units from one site to another. In forestry, this might be the movement of seedlings of known heritage from a nursery to a specific configuration in a PROGENY TEST or to operational plantations.

DEPLOYMENT ZONE: A geographic area, defined mainly by genetic adaptation criteria, for which tree improvement materials are produced. Deployment zones include breeding regions, SEED PLANNING UNITS, and SEED ZONES.

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 crosses each parent as both a male and a female to all other parents reciprocally and including self-matings. A 5-parent (5×5) diallel requires 25 matings.

DIOECIOUS: A tree species having female and male sex organs on different plants

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 to refer to the portion of non-additive genetic variance estimated by full-sib/half-sib mating designs. With dominance, the average value of an individual is not intermediate between the average values of it’s two parents.

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

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EFFECTIVE POPULATION SIZE: The average number of individuals in a population that contribute genes to the succeeding generations. In British Columbia, the effective population size Ne of a seedlot is the harmonic mean contribution of parent trees to a seedlot, calculated using the formula Ne = 1/Ïpi2 where pi is the average female and male contribution to a seedlot of parent i.

ECOTYPE or ECOTYPIC VARIATION: Genetically differentiated populations distinguished from each other by sharp discontinuities in character expression. Ecotypic variation is a result of adaptive selection. Ecotypes may be geographic, climatic, elevational, or edaphic.

EDGE EFFECTS: Phenotypic differences between trees due to their proximity to the edge of a stand or of a test area (such as a progeny test). Usually due to trees near the edge being less shaded by surrounding trees and thereby receiving more light

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

ELITE TREE: A tree verified as superior or desirable for traits of interest (usually commercial traits such as growth rate) 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 and PLANTLING for parallel terminology.

EMBRYO: The portion of the seed resulting from the union of male and female gametes, that has the potential to develop into a mature plant

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.

ENDEMIC: Species or population(s) native to a small region and found nowhere else.

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 light 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 inter-locus 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.

EUCLIDEAN DISTANCE: A straight-line distance between the end points of two vectors. Used to calculate “climate distance” using multiple climate variables.

EUCLIDEAN CLIMATE DISTANCE: As used in BC, the euclidean climate distance (ECD) uses euclidean distance mathematical equations based on seven climate variables that are known to influence the natural range of species and populations of indigenous trees. The ECD provides a representation of the climate distance between geographic points based on multiple, biologically relevant, climate variables such as mean annual temperature.

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

EXOTIC SPECIES: An introduced species that is not native to an area. Usually this refers to long distance transfers of a species, such as introducing Pinus radiata to New Zealand or Eucalyptus spp . to Brazil.

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

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-, F3 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, etc. In forestry, F1 crosses are generally considered as crosses among tested or non-tested parent trees selected from wild stands. F2 progeny are derived from mating among trees derived from F1 crosses, etc.

FACTORIAL MATING: A mating scheme in which M males are each crossed to the same group of Nfemales to form a
M x N factorial. For example, if 2 trees designated male are crossed to each of 3 trees designated as females, a 2×3 factorial with 6 total crosses is formed.

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 for vegetative propagation (i.e. yellow cypress). Trees in the hedges are identified for one or both parents, such that the trees in the hedges are known to be from the same full-sib or half-sib family or families. Cuttings may be bulked from all families in the hedges in known proportions to form a bulked vegetative lot, or kept separate by family with out-planting done in family groups.

FARM-FIELD TEST: A progeny or genecology test done at close spacing on a site prepared to agricultural farm standards with homogenous soil conditions and control of weeds to reduce effects due to a heterogenous environment and to increase the relative genetic effects. Usually used for early selection.

FECUNDITY: A measure of reproductive productivity relative to other individuals in a population.

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

FOUNDATION STOCK: The ultimate source of material for a clone. Often the ORTET and primary RAMETS.

FULL-SIB PROGENY: The offspring resulting from a cross of two known parents (see FAMILY).

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GAMETE: A male or female reproductive cell capable of uniting in the process of fertilization with another gamete of the opposite sex to develop into an embryo.

GAMETOPHYTE: In trees this is the is the haploid (1n) phase that contains genetic material from a single parent, such as a pollen grain (male) or ovule (female).

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 FLOW: The movement of genes from one population of a species to another whereby the genes become established in the receiving population through successful reproduction. For trees this could be the transfer of genes to new areas through pollen or seed movement.

GENE FREQUENCIES: The proportion of a population that contains a particular gene. Usually expressed between 0 (no individuals contain the gene) to 1, all individuals have the gene.

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

GENE POOL: All of the genes contained in all of the individuals within the defined population.

GENECOLOGY: The study of patterns of genetic differentiation among populations of a species and how this genetic differentiation is patterned on factors of the environment in which they live. For example, the study of how lodgepole pine from different natural populations grows in relation to climatic factors across its natural range.

GENERAL CIRCULATION MODELS: (GCM) are mathematical climate models that represent physical process in the global atmosphere, oceans, and the land surface. They are often used to simulate climate response to increasing greenhouse gas concentrations.

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

GENETIC CLASS A: Seed from seed orchards or vegetative material from family or clonal hedges that have a Genetic Worth greater than ‘zero’. Class A seed is a term used in British Columbia that is not used in other parts of the world.

GENETIC CLASS B+: Seed and vegetative material derived from natural stands that are 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 considered to have a Genetic Worth of zero .

GENETIC DIVERSITY: The variation of genes within a species, a population, or an individual.

GENETIC DRIFT: The change of gene frequency (the change in the proportion of individuals in a population with a given gene) or genotype frequency due to the chance disappearance or concentration of particular genes through reproduction or through mortality. Genetic drift is non selective, in that it is due strictly chance and not to natural or artificial selection acting on a population. Genetic drift can be high in small populations and is usually low in large populations.

GENETIC ENGINEERING: Inserting, suppressing, or removing genetic material from a tree at the DNA level.

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

GENETIC GAIN: The average (heritable) difference in offspring performance between a selected tree or population relative to a natural population for a specific trait. In BC genetic gain is quantified as a breeding value (BV) for a specific parent tree, or as a the genetic worth of a seedlot.

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

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

GENETIC WORTH (GW): A measure of the genetic quality of a seed or vegetative lot relative to natural or wild stand material, measured for a specific trait (i.e., growth, wood density, pest resistance). Calculated as the average breeding value (or clonal value) of parent trees (or clones) contributing to a seedlot (or cutting lot) weighted by the relative contribution of the parents (or clones) to the lot. This term is used in forestry in British Columbia.

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


GENOME: All the DNA of a living organism.

GENOMICS: the study of the structure, function, evolution, and mapping of GENOMES

GENOTYPE: The genetic composition of an individual.

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


GRAFT INCOMPATIBILITY: A destructive interaction between tissues of the ROOTSTOCK and SCION, often resulting in death of the scion or ramet and/or 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, replicating the original ortet or parent tree. In forestry in British Columbia, most RAMETS in a seed orchard are grafted plants using scion from a known PARENT TREE.

GxE INTERACTION: (GENOTYPE by environment interaction) The relative magnitude of differences in performance (for a trait such as growth) of a set of provenances, families, or clones by test location, by test year, or by test age. A forestry example is a difference in the rankings of the same set of families when planted on a series of test sites in different environments.

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HALF-SIB PROGENIES: Offspring with one known common parent multiple unknown other parents. In forestry, open-pollinated seed from a tree have a known female parent, but the male parents are unknown.

HARDENING OFF: The exposure of seedlings or other propagules to environmental conditions that cause them to become dormant in preparation for field planting. For example, the hardening off seedlings grown in a nursery through drought or increased night length to induce bud set and dormancy.

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 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 production of scion.

HERITABILITY: The ratio of genetic variance to phenotypic variance. See also NARROW-SENSE HERITABILITY and BROAD-SENSE HERITABILITY. Used as a measure of the degree of genetic control of a particular trait within a population.

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

HETEROSIS: The average of the progeny differs from the average of the parents. Sometimes called hybrid vigor.

HETEROZYGOSITY: See HOMOZYGOSITY. When both alleles at a locus are not identical.

HOMOZYGOSITY: When both alleles at a locus are identical (i.e. alleles represented by aa or AA at a locus are 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 genotypes within a population.

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IDEOTYPE: An idealized multi-trait characterization; for example, a tree crown that is long, narrow and dense, with perpendicular branch angles.

IN SITU : On site; within the natural habitat.

INTER SITU : In forestry, genetic material maintained in genetic tests, such as PROGENY TESTS and PROVENANCE TESTS, that is part of the genetic resource contributing to an overall strategy of genetic conservation that also considers IN SITU and EX SITU (seed in storage) genetic resources.

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 that is based on the proportion loci with alleles that are identical by descent from a common ancestor. F values range from 0.0 (no inbreeding) to 1.0 (fully inbred). A negative F can occur and indicates outcrossing and greater heterozygosity than in the base population (for trees the base population would normally be a natural stand).

INBREEDING: A reduction in average HETEROZYGOSITY resulting from a mating between relatives, such that some proportion of the loci in an individual have identical alleles that come from a common ancestor.

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. Species such as redcedar have indeterminate growth as new leaves can form from the apical meristem as a tree grows.

INTROGRESSIVE: The moving of genes from one species or population to another by repeated backcrosses.

ISOZYMES: Enzymes having similar structure, catalyzing the same reaction, and produced at different loci.

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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: The area of leaf surface relative to the unit area of ground.

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

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MARKER GENE: A gene or DNA sequence that can be used alone or in combination with other marker genes to identify a species, or individuals within a species, with specific traits.

MATERNAL EFFECTS: A special case of ‘C-EFFECTS’ that is due to a common maternal environment. Frequently associated with the non-genetic effect of environment on the performance of seed from a parent tree.

MATURATION: For trees, the process of development from seed to seedling, sapling, and mature tree.

MEGAGAMETOPHYTE: In a conifer, the haploid tissue that develops within an ovule, producing egg cells within multiple archegonia and providing nutrition to a developing embryo after fertilization. In conifer seeds, this is the soft, whitish, and waxy tissue surrounding the embryo.

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: The binary system by which alleles segregate at meiosis and recombine through fertilization. First observed by Gregor Mendel using peas.

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

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

MICROSPOROGENESIS: The development of pollen.

MONOECIOUS: A tree species capable of having both female and male sexual organs on the same plant. Most conifers are monoecious.

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.

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.

NATURAL RANGE: The geographic area naturally occupied by a species (or other taxon), within the more recent post-glacial era and prior to anthropogenic influences on the species range.

NATURAL SELECTION: The process by which the genetic makeup of a population changes under natural conditions, without human interference.

NEUTRAL ALLELES: Alleles subject to no (or very weak) selection pressure, and thus useful as evolutionary clocks, for mating-system estimation, and for understanding some important population-genetic parameters.


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

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

OPEN-POLLINATED PROGENY: Progeny from a mating that is not controlled, whereby a mixture of related and unrelated pollen is delivered by wind, or in some cases by insects etc.

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

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

OVERDOMINANCE: A special case of dominance in which the phenotype of the heterozygote individual(s) is, on average, outside the range of the average phenotype of the homozygote parents.

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PARENT TREE: A tree selected for traits of interest based on progeny or clonal testing.

PEDIGREE: A record of parentage. Often includes data on performance of the parents and 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.

PHENOLOGY: The timing of periodic life-cycle phenomena such as flowering, growth initiation, growth cessation, or bud set.

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. High plasticity occurs when the same genotype can have a very different phenotype in contrasting environments.

PHOTOPERIOD: Day length or the length of time with sufficient light to influence growth or phenology response in a plant. Natural photoperiod may be extended with artificial lighting or reduced with black-out, as is sometimes done in seedling nurseries to influence phenology and growth patterns.

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

PHYTOHORMONES: A broad class of naturally occurring chemicals that are effective in very low concentrations at regulating plant growth and development.

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

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 selected for its outstanding phenotype for traits of interest such as growth, stem form, or pest resistance, but not yet progeny or clonally tested for it’s ability to pass these traits on to offspring.

POLYGENIC: 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 or POLYCROSS: A mating scheme in which pollen from several (often 10 or more) usually unrelated trees are mixed and used to pollinate a series of other trees, which act as females.

POLYMORPHISM: The occurrence of two or more clearly different forms (morph) or alternative phenotypes in a population of trees.

POPULATION: A group of individuals of the same species that occupy a particular geographic area or region and have some degree of genetic similarity relative to comparisons between populations. In general, individuals within a population have some probability of interbreeding and exchanging genes with each other.

PRECOCIOUS: In the reproductive sense, to reproduce (produce cones and pollen) 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.

PRODUCTION CLONES: Clones maintained in large enough stoolbeds, hedges, cultures, etc. to supply large numbers 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, such as the parent trees in a seed orchard.

PROGENY TEST: Generally a common-garden test with one or more test sites in which the breeding values of parents are evaluated and ranked on the basis of the performance of their offspring. In forestry, families are usually tested on multiple progeny test sites located on logged areas within the seed zone of interest.

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

PROGENY TRIAL: One or more progeny tests in which the same group of pedigreed progeny are evaluated for traits of interest.

PROVENANCE TEST: A common-garden test in which population samples (usually seeds) from stands of known natural origin are grown together in a planned experimental design at one or more locations to evaluate the relative performance of the provenance samples in test environments of interest.

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

PROVENANCE TESTED: Seed sources that have been tested in provenance tests.

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RAMET: All vegetative propagules of an ORTET are ramets. A clone is composed of the ortet and its ramets (i.e. grafted trees in seed orchards consist of ramets of parent trees that are the ortets)

RAMICORN: A large high-angled branch that often results from one shoot of a forked leader being partly suppressed by the more dominant shoot.

RANDOM MATING: A situation in which there is no selection influencing which individuals mate. In practice, this is never the case, however, with many tree species, pollen clouds mix and mating between trees in natural situations can often be considered near random.

RECIPROCAL RECURRENT SELECTION: A breeding scheme in which selection within each of two independent pedigreed lines of trees is based on progeny test results of families derived from 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 on a chromosome.

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).

REJUVENATION: A change in a tissue or an organism from a more mature state to a more juvenile one, such as restoring more juvenile yellow cedar foliage through hedging.

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. 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 way to note the departure of an individual clone from the performance of its sibs. SCA may also refer to the degree of non-additive genetic variation in a population.

SCION: A plant part, often a twig, that is grafted onto the root-bearing part of another plant. See stock.

SEED PRODUCTION AREA (or stand): A plantation or natural stand designated for repeated collection of seeds for reforestation purposes.

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: (also SEED PROCUREMENT AREA) The geographic source of a seed. If a natural stand, equivalent to provenance.

SEEDLOT: A quantity of seeds from the same species, source, quality, and year of collection.

SEED ZONE: A geographic area in which seed from defined genetic populations can be planted or moved. In forestry, provenance test or other information is generally used to determine the geographic area in which a defined genetic population (such as seed from a particular seed orchard or provenance) can be planted and is genetically adapted to the environment of the seed zone.

SEED PLANNING UNIT (or ZONE): Similar to seed zone. The geographic area within which seed needs, and the planning of programs such as breeding or seed orchards, are organized for management purposes.

SELECT SEED: Seed and vegetative material having a level of genetic gain greater than zero for some trait of interest. In British Columbia, seedlots registered as select are assigned a GENETIC WORTH for one or more traits.

SELECTABLE MARKER: May be used in marker-assisted selection, or to select a transformed genotype from a mixture of transformed and non-transformed cells.

SELECTION INTENSITY: (a) The standardized selection differential between the average of the selected population and the average of the population selected from, or (b) The percentage of individuals selected from a candidate population.

SELFING: When an individual mates with itself. In trees, self-pollination occurs when a tree is pollinated with pollen from the same tree or clone.

SERIAL PROPAGATION: When an ortet provides cuttings or tissue that become primary ramets, some of which in turn are later used as donors of cuttings or tissue that become secondary ramets, etc.

SOMATIC CROSSING-OVER: An exchange of genetic material between homologous chromosomes in somatic cells, 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.


STABILITY (genetic): The degree to which phenotype remains unchanged or similar across a range of different environmental conditions, such as seedlings from a parent tree that express a similar phenotype (or rank relative to other families of seedlings) across a planting sites representing a broad environmental range. Also see PHENOTYPIC PLASTICITY.

STECKLING: A rooted cutting that is sufficiently developed so that it can be or has been planted in the field.

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. Often used to describe a seedling age and the size of container it is grown in.

SUBLINES: A separation of parent trees in a breeding population into groups or lines that are mated together. Used in tree breeding programs to control inbreeding such that all inbreeding is accumulated within sublines. Production populations are drawn from individual sublines such that parent trees from different sublines are unrelated and will have outcrossed (non inbred) progeny when they mate in a production population such as a seed orchard..

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 provenance trials. Typically referred to as B+ in British Columbia.

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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 branches, resulting 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.

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 method of genetic engineering, such as CRISPR.

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

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. For example, selecting all trees in a breeding population above a certain height.

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

VARIANCE: A statistical measure of the differences between individuals in a tested population. Variance may be divided into various components to provide information such as (for example) how genetic and environmental effects influence tree growth.

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: Plant material produced asexually, such as cuttings of yellow cedar or poplar.

VEGETATIVE MULTIPLICATION: The clonal reproduction of parent trees or seedlings from parent trees by rooting cuttings, grafting, or tissue culture, or of embryos through somatic embryogenesis.

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

VIABLE POPULATION: A population, which maintains its genetic diversity, potential for evolutionary adaptation, and is at minimal risk of extinction from demographic fluctuations, environmental variations, or other causes of mortality.

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

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WILD POPULATION: A population of a species within its natural range in which the individuals are the result of natural reproduction.

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