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Glossary allele One of two or more alternative forms of a gene, differing in DNA sequence and affecting the functioning of a single gene product (RNA and/or protein). Any of the alternate allele forms may occupy the same site or locus on a pair of homologous chromo- somes. allelic frequency The percentage of all alleles at a given locus in a population gene pool represented by a particular allele. artificial selection A form of selection that is superimposed on natu- ral selection by breeders in an effort to change various traits in preferred stocks. backcross A cross of heterozygous offspring with individual geno- typically identical to one of its parents. biodiversity (biological diversity) The variety and variability among living organisms and the ecological complexes in which they oc- cur. blastocyst The mammalian embryo at the time of its implantation into the uterine wall. blastomere A cell produced during the splitting of a fertilized egg. breed For the purposes of this report and in general, an interbreed- ing group with some identifiable common appearance, perfor- mance, ancestry, selection history, or other feature. chromosome A thread-like structure of the cell's nucleus that carries genetic information arranged in a linear sequence. 245
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246 / Glossary clone A group of genetically identical cells or organisms all de- scended from a single common ancestral cell or organism. conservation The management of human use of the biosphere so that it may yield the greatest sustainable benefit to present gen- erations while maintaining its potential to meet the needs and aspirations of future generations. crossbreeding The mating members of two genetically distinct popu- lations. In the context of this report, mating among two or more different breeds. cryobiology The study of the effects of extremely low temperature on biological systems. cryopreservation Maintaining tissues, semen, eggs, or embryos for the purpose of long-term storage at ultralow temperatures, typi- cally between -150°C and -196°C; produced by storage above or in liquid nitrogen. cytogenetics The combined study of cells and genes at the chromo- some level. data base Refers to a system usually computer-based in which information is compiled in an organized, retrievable manner. diploid Possessing twice the number of chromosomes as the number present in reproductive cells such as eggs. The somatic number of chromosomes (2N). DNA Deoxyribonucleic acid. Each DNA molecule has two strands of complementary nitrogenous base pairs structurally arranged in a double helix. It is the molecular basis of heredity in many organisms. DNA hybridization A technique for determining the degree of simi- larity of DNA base sequences in two species, involving radioiso- tope labeling of DNA from one species and annealing it to the DNA of the other species. DNA sequencing A method for determining the sequence of base pairs in sections of DNA. ecosystem A community of organisms interacting with one another; the environment in which organisms live and with which they also interact. effective population size The estimated number of individuals in a population that contribute genes to succeeding generations, ac- counting for factors such as unequal sex ratio of breeding indi- viduals, variation in number of offspring per parent, and changes in breeding population size over time.
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Glossary / 247 electrophoresis The differential movement of charged molecules in solution through a porous medium in an electric field. The po- rous medium can be filter paper, cellulose, or, more frequently, a starch or polyacrylamide gel. electrophoretic analysis A method commonly used to separate pro- teins and other organic molecules. embryo The early or developing stage of an organism, especially the developing product of egg fertilization. embryo transfer Artificial introduction of a recently formed embryo into the oviduct or uterus of the biological mother or of a surro- gate mother. endangered In the context of this report, a term that applies to taxa (species, subspecies, population) in danger of extinction and for which survival is unlikely if the causal factors of loss continue. enzyme One of a large group of proteins, produced by living cells, that act like catalysts in essential chemical reactions in living tis sues. exotic Relating to an organism that is found in, or is intentionally introduced into, an area where it does not.naturally occur. extensive management The production and management system under which domestic livestock has traditionally been raised, generally under range conditions. Nutritional supplementation and veteri- nary care are minimal or nonexistent. Animals are subjected to a variety of environmental and nutritional stresses and become adapted to their local environments. extinct In the context of this report refers to taxa (e.g., populations, subspecies, species) not found after repeated searches of known and likely areas. fecundity Potential fertility or the capability of repeated fertiliza- tion. Specifically, it is the quantity of eggs, produced per female, over a defined period of time. feral Pertaining to formerly domesticated animals now living in a wild state. flock Temporary management units, or groupings of animals, on a given farm that are not necessarily maintained in reproductive isolation and may not be genetically different. flow cytometry A method for rapidly measuring cells. gamete A mature reproductive cell (egg or sperm) that is capable of fusing with another similar cell of the opposite sex to produce a zygote (fertilized egg).
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248 / Glossary gene The basic functional unit of inheritance that occupies a specific position within a chromosome or genome and is responsible for the heritability of particular traits. gene flow The movement of genes through or between populations as the result of crossbreeding and natural selection. gene mapping Assignment of a gene locus to a specific chromosome within a genome and/or determining the sequence of genes and their relative distances from one another on a specific chromo- some. gene pool The totality of genes and their alleles within an inter- breeding population. gene transfer Refers to the identification and isolation of a gene from one genome and its transfer into the genome of another individual. Transfers may be within the same species or from one species to another. genetic conservation To maintain a reservoir of potentially useful genetic variation from that contained in the multitude of breeds and varieties. genetic distance A measure of the number of allelic substitutions per locus that have occurred during the separate evolution of two populations or species. genetic diversity In a population or species, the possession of a variety of genetic traits that frequently result in differing expres- sions in different individuals. genetic drift The variation of allele frequencies from one generation to the next due to random fluctuations. In small populations this can lead to significant changes. genetic resources Organisms from which the genes needed by breeders and other scientists can be derived. genetic risk In the context of this report, the potential for an activity or event to result in loss of genes from a species or population. genome A single complete set of the genes or chromosomes of an individual. Typically, gametes such as egg cells contain a single set and are termed haploid, while the somatic cells that comprise the bulk of the living tissue of the plant body contain two sets and are diploid. genomic library A collection of transgenic DNA molecules (cloned fragments) that is representative of individual genomes. genotype The genetic constitution of an organism, as distinguished from its appearance. The genotype may or may not be expressed, in appearance or performance, depending on the environmental effects of a given location. See phenotype.
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Glossary / 249 genotype-environment interaction Where the phenotypic expres- sion of a genotype differs when measured under different envi- ronmental conditions. germplasm The tissue, semen, eggs, embryos, or juvenile or mature animals useful in breeding, research, and conservation efforts. germplasm bank An institution or center that participates in the management of genetic resources, in particular by maintaining ex situ or in situ collections; the term also can refer to a collection of genetic resources rather than the institution holding it. germplasm collection A collection of many different varieties, spe- cies, or subspecies that represent a diverse collection of geno- types and, hence, genetic diversity. i: habitat The place where an organism is usually found; its natural environment. herd See flock. herdbooks Records of pedigrees and breeding stocks selected for performance that began to appear in eighteenth-century Europe. heterosis Increased vigor in terms of growth, fertility, or other char- acters in individuals which resulted from a cross of two geneti- cally different populations. heterozygous Having one or more unlike alleles at corresponding loci of homologous chromosomes. homologous chromosomes Chromosomes in a cell that have the same visible structure and linear sequences of genes. homozygous Having like alleles for a particular gene at correspond- ing loci on homologous chromosomes. hybrid The product of a cross between two species, races, or geneti- cally distinct individuals. hybridization The process of crossing individuals that possess dif- ferent genetic makeups. n vitro fertilization Fertilization of an egg outside the female body. inbreeding The mating of related individuals. industrialized stocks Livestock reared in uniform, high-quality con- ditions so that minimal selection effort is necessary for environ- mental adaptation. Often breeders begin to develop one highly selected strain for specific production traits, and it comes to dominate production. intensive management Production and management systems for do- mestic livestock that involve high levels of inputs, such as supple- mental feed and veterinary care and require greater management effort.
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250 / Glossary isozyme (isoenzyme) Different chemical forms of the same enzyme that can generally be distinguished from one another by electro- phoresis. kilobase (kb) A measure of nucleic acid length consisting of 1,000 nucleotides. landrace A population typically genetically heterogeneous, that is specifically adapted to a set of local conditions. line A term used in the livestock breeding industry to indicate a group of individuals of a given breed that are maintained in re- productive isolation from other members of the breed to develop potentially advantageous production traits. linkage group A group of genes that are in close proximity on the same chromosome and, therefore, are generally inherited together. livestock Domesticated animals that are generally associated with various types of agricultural production and are used as sources of draft power, food, or fiber. They include cattle, horses, pigs, chickens, sheep, and goats. locus (plural, loci) The position that a gene occupies in a chromo- some. major domesticates The 40 domesticated mammalian and avian spe- cies that are used extensively on a global scale due to their adapt- ability and utility and because cultural preferences for them have developed. minor domesticates The domesticated mammalian and avian spe- cies that are less abundant globally than major domesticates but are critically important because of their relative abilities to pro- duce in environmental niches and because of traditional or cul- tural patterns of use for their products. mitochondrial DNA In animal cells, DNA found outside of the nucleus in small, ablate bodies called mitochondria. morula An embryo that consists of a cluster of cleaving blastomeres; a stage prior to the blastula. multiple ovulation An animal reproduction technology involving the hormonal treatment of the donor female to induce ovulation and to produce greater numbers of embryos per donor female. mutation A gene that is modified as a result of structural change. The individual that results may be referred to as a mutant. The term also can be applied to the process producing such genetic change.
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Glossary / 251 natural selection The differential fecundity in nature between mem- bers of a species possessing adaptive characters and those with- out such advantages. Oocyte An egg before fertilization. Outcross the mating of genetically unrelated individuals from ge- netically different accessions, breeding lines, populations, or spe- cies. ovum A mature egg; female gamete. This term can also refer to a Reimplantation embryo. phenotype The sum total of the environmental and genetic (heredi- tary) influences on an organism; the visible or measurable char- acteristics of an organism. The degree to which these characteris- tics become manifest is often determined by the interaction of the alleles that comprise the genotype with environmental factors. See genotype. polymorphism Having more than one form or structural pattern. In genetics this can refer to the existence within a population of several alternative alleles at a single locus. population A group of organisms of the same species that occupy a particular geographic area or region. In general, individuals within a population potentially interbreed with one another. population genetics The study of the genetic composition and dy- namics of populations. preservation That aspect of conservation by which a sample of an animal genetic resource population is designated to an isolated process of maintenance, by providing an environment free of the material and human forces that might bring about genetic change. progeny testing The evaluation of the genotype of a parent by a study of its progeny under controlled conditions. quantitative genetics The branch of genetics that is concerned with measurable traits determined by several pairs of genes. See quan- titative traits. quantitative traits Traits determined by the cumulative action of many genes, usually in concert with environmental factors. rare In the context of this report, taxa with small populations that are not currently endangered but that are at risk of loss. reproductive isolation The inability of two populations or species to produce fertile offspring or interbreed as a consequence of physi- ological or genetic incompatibility or environmental barriers.
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252 / Glossary restriction endonuclease Any one of many enzymes that cleave DNA molecules at specific recognition sites. They are coded for by genes called restriction alleles. restriction fragment length polymorphism Variation that occurs within a species in the length of DNA fragments resulting from diges- tion of the extracted DNA with one of several enzymes that cleave DNA at specific recognition sites. Changes in the genetic compo- sition result in fragments of altered length. selection Any natural or artificial process that permits an increase in the proportion of certain genotypes or groups of genotypes in succeeding generations in relation to others. semen immunoextension A method of adding antibodies to specific antigens of the pathogens potentially found in semen to control specific diseases and prevent transmission in the semen. semen screening A method for verifying the health status of semen samples. species A taxonomic subdivision; a group of organisms that actually or potentially interbreeds and is reproductively isolated from other groups. stable A system that returns to its initial conditions after being dis- turbed. stock See line. strain See line. tandem repeat Two identical chromosomal segments that lie one behind the other. The order of the genes in each segment is the same. transgenic animal An animal into which cloned genetic material has been experimentally transferred. type A distinction defined by the production characteristics of live- stock species. For example, there are two types of cattle, meat and dairy; two types of sheep, hair and wool; and two types of chickens, layers and broilers. Many different breeds can be found within a given type. unique Having distinct characteristics that are not found in another breed or type. wild species Organisms in or out of captivity that have not been subject to breeding to alter them from their native (wild) state.
Representative terms from entire chapter: