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Managing Global Genetic Resources: Agricultural Crop Issues and Policies Glossary A accession A distinct, uniquely identified sample of seeds, plants, or other germplasm materials that is maintained as an integral part of a germplasm collection. active collection Germplasm accessions that are maintained under conditions of short- and medium-term storage for the purpose of study, distribution, or use. allele A contraction of allelomorph; any of a number of alternative forms of a gene. The forms differ in DNA (deoxyribonucleic acid) sequence and affect the functioning of a single gene product(RNA [ribonucleic acid] or protein). New alleles arise from existing ones through mutation. The alleles of a gene occupy the same site or locus on a chromosome. aneuploid An unbalanced genome with extra or missing chromosomes, having more or less than an integral multiple of the haploid number of chromosomes. anther culture The culturing of the part of the stamen that bears the pollen grains (anther) or of a single pollen grain, as a method of producing haploids, homozygotes, or all-male plants. apomixis Asexual reproduction in plants through the formation of seeds without fertilization (agamospermy), or the formation of a new individual from a group of cells without the production of an embryo or seed (vegetable reproduction). B base collection A comprehensive collection of germplasm accessions held for the purpose of long-term conservation; stocks from the
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Managing Global Genetic Resources: Agricultural Crop Issues and Policies base collection replenish exhausted or expired stocks in the active collection. biological diversity The variety and variability among living organisms and the ecological complexes in which they occur. bisexual Having both sexes. breeding line A genetic group that has been selected and bred for their special combinations of traits. C characterization Assessment of the presence, absence, or degree of specific traits that are largely morphological and little influenced in their expression by varying environmental conditions. chromosome The structure in the cell nucleus on which genes are located. clonal propagation The reproduction of plants through asexual means, such as cuttings, grafts, or tissue culture. clone A group of genetically identical individuals that result from asexual, vegetative multiplication; any plant that is propagated vegetatively and that is therefore a genetic duplicate of its parent. collection A sample (for example, variety, strain, population) maintained at a genetic resources center for the purposes of conservation or use (an accession); a group of collected samples. cultivar A contraction of cultivated variety. See also variety. cytogenetics The combined study of cells and genes at the chromosome or cytoplasmic level. cytoplasmic (mitochondrial) gene The mitochondrial DNA that is found outside of the nucleus in small, oblate bodies called mitochondria. D deoxyribonucleic acid (DNA) The basis of heredity; the substance of the genetic code. distribution To supply adequate samples of genetic resource stocks to breeders and other users. E effective population size The equivalent number of parents if all contributed the same number of progeny to the next generation. enhancement The process of improving a germplasm accession by breeding while retaining the important genetic contributions of the accession. This process may entail simple selection. epistasis The interaction of genes at different loci. The situation in which one gene affects the expression of another. evaluation The assessment of plants in germplasm collection for potentially useful genetic traits, many of which may be environmentally
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Managing Global Genetic Resources: Agricultural Crop Issues and Policies variable (for example, pest or disease resistance, fruit quality, flavor, yield). exploration The search for materials in the field. ex situ conservation Maintenance or management of an organism away from its native environment. For crop germplasm, this term typically refers to maintenance in seed banks or repositories. F folk variety Local varieties of cultivated plants developed by indigenous farmers in traditional agricultural systems. By modern standards, such varieties are often highly variable genetically. G gene The basic functional unit of inheritance. gene pool All the genes within a population. genetic diversity In a group such as a population or species, the possession of a variety of genetic traits and alleles that frequently result in differing expressions in different individuals. genetic drift The random fluctuations of gene frequencies due to sampling effects or unintended selection; although genetic drift occurs in all populations, its effects are most evident in small populations. genetic resources In the context of this report, the term is synonymous with germplasm. See germplasm. genetic stocks Accessions that typically possess one or more special genetic traits that make them of interest for research. genetic vulnerability The condition that results when a crop or a plant species is genetically and uniformly susceptible to a pest, pathogen, or environmental hazard. genome The complete set of chromosomes found in each cell nucleus of an individual. The haploid nucleus of gametes (sperm or egg) contains one genome. The diploid cells that make up the bulk of the living tissue of the plant body contain two sets. genotype In the context of this report, plants with a specific complement of genes. germplasm Seeds, plants, or plant parts that are useful in crop breeding, research, or conservation because of their genetic attributes. Plants, seed, or cultures that are maintained for the purposes of studying, managing, or using the genetic information they possess. green revolution Increased production from the introduction of high-yielding varieties of major grain crops that were also aided by the more intensive use of fertilizers and irrigation. H haploid A cell or organism with a single genome. heterozygous Having different alleles at a locus.
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Managing Global Genetic Resources: Agricultural Crop Issues and Policies hybrid The progeny of a cross between two different species, races, cultivars, or breeding lines. hybridization The process of crossing individuals that possess different genetic makeups. I inbreeding The breeding of individuals that are related. in situ conservation Maintenance or management of an organism within its native environment. For landraces, this term includes maintenance in traditional agricultural systems. isoallele An allele whose effect can only be distinguished from that of the normal allele by special tests. isoenzyme (isozyme) Different chemical forms of the same enzyme that can generally be distinguished from one another by electrophoresis. isogenic Genetically identical individuals or lines except for one or a few genes. L landrace A population of plants, typically genetically heterogeneous, commonly developed in traditional agriculture from many years of farmer-directed selection, and which is specifically adapted to local conditions. legume Any member of the pea or bean family (Leguminosae or alternately, Fabaceae), for example, beans, peanuts, and alfalfa. M multiallelic genetic stock For cultivated plants, includes multiple gene marker stocks that are useful for linkage studies; also stocks with special combinations of loci necessary for the expression of a single trait. N neutral allele Those alleles whose differential contributions to fitness are so small that their frequencies change more owing to drift than to natural selection. nominal population size Number of individuals per generation. null hypothesis The standard hypothesis used in testing the statistical significance of the difference between the means of samples drawn from two populations. It states there is no difference between the populations from which the samples are drawn. If the probability is 0.05 or less, the null hypothesis is rejected and the difference is said to be significant. O obsolete variety Plant varieties that are no longer grown commercially; such varieties may be maintained in collections for use in breeding programs.
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Managing Global Genetic Resources: Agricultural Crop Issues and Policies outbreeding The crossing of genetically unrelated plants or animals; crossbreeding. P passport data Information about a sample or specimen and the collection site, recorded at the time of collection. This information should include time of collection, exact location, identifying characteristics, ecological condition of location, names and numbers assigned to the accession by the collector, and any other relevant observations. perennial crops Crop plants for which individuals are productive over several years. They include herbaceous perennials that die back annually, such as asparagus, and woody perennials with stems that may live for many years, such as apples, citrus crops, or mangos. phenotype The combined expression of the environmental and genetic (hereditary) influences on an organism; the visible characteristics of an organism. plant breeders' lines Unreleased lines or parents of hybrids maintained by breeders as part of their working stocks. Breeders usually develop and carry many lines of which only a small number are ever released into commercial production. pleiotropy The phenomenon of a single gene being responsible for more than one phenotypic effect. polymorphic In the context of this report, plants with several to many variable phenotypic or genetic forms. population A group of individuals of the same species that occupy a particular geographic area or region. In general, individuals within a population potentially interbreed with one another. preservation Storage of materials in collections under conditions that promote long-term survival and the use of propagation methods that protect genetic integrity during regeneration. primary gene pool For plants, a cultivated species and its wild relatives that are readily intercrossed so that gene transfer is relatively simple. primitive variety See folk variety. pyramiding A strategy for developing long-lasting genetic resistance in a cultivar by combining two or more different genes that confer similar resistance into the same breeding line. Q quarantine Measures that isolate introduced stocks to ensure that they do not carry diseases or pests injurious to the stocks in the importing country. R rare Small populations that are not currently endangered, but that are at some risk of loss.
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Managing Global Genetic Resources: Agricultural Crop Issues and Policies regeneration Grow-out of a seed accession for the purpose of obtaining a fresh sample with high viability and adequate numbers of seeds. restriction fragment length polymorphisms (RFLP) Variation that occurs in the length of DNA fragments resulting from digestion of the extracted DNA with one of several restriction enzymes that cleave DNA at specific recognition sites. Changes in the genetic composition result in fragments of altered length. S secondary gene pool For plants, all the biological species that can be crossed with a cultivated species, but where hybrids are usually sterile. Gene transfer is difficult but not impossible. seed viability The ability of a seed to germinate under appropriate conditions. single-gene or single-trait variants Lines that carry variants for qualitative characters. Examples include differences in morphological and physiological characters, electrophoretic variation in proteins, and fragment length variation in DNA generated by restriction enzymes. species A taxonomic subdivision; a group of morphologically similar organisms that actually or potentially interbreed and are reproductively isolated from other such groups. T tertiary gene pool For plants, those species that can be crossed with a cultivated species only with difficulty and where gene transfer is usually only possible with radical techniques. Biotechnology has, at least in theory, greatly enlarged this pool because transformation (a radical technique) makes possible the introduction of DNA from any species. tissue culture A technique for cultivating cells, tissues, or organs of plants in a sterile, synthetic medium; includes the tissues excised from a plant and the culture of pollen or seeds. tuber A thickened, compressed, fleshly, usually underground stem that may function as a storage organ for food (starch) or water, or for propagation. V variety A plant type within a cultivated species that is distinguishable by one or more characters. When reproduced from seeds or by asexual means (for example, cuttings) its distinguishing characters are retained. The term is generally considered to be synonymous with cultivar. W weed A plant growing where it is not wanted by humans. wild and weedy relatives For plants, those species that share a common ancestry and ecogeographic area with a crop species but that have
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Managing Global Genetic Resources: Agricultural Crop Issues and Policies not been domesticated. Most crops have wild or weedy relatives that differ in their degree of relationship to the crop. The ease with which genes can be transferred from them to the crop varies. wild species Species that have not been subject to breeding to alter them from their (wild) state.
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