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APPENDIX c Glossary * Adaptive immunity. Lymphocyte-, macrophage-, or dendritic cell-based systems that en- counter, memorize, and recall new antigens (old term: immunity). Allele. Any alternative form of a gene that can occupy a particular chromosomal locus. In humans and other diploid organisms there are two alleles, one on each chromosome of a homologous pair. Aneuploidy. Gain or loss of one or more chromosomes. Antibody. An immunoglobulin molecule that has a specific amino acid sequence by virtue of which it interacts with the antigen that induced its synthesis in cells of the lymphoid series (especially plasma cells) or with an antigen closely related to it. Antigen. Any substance that is capable under appropriate conditions of inducing a specific immune response and of reacting with the products of that response, that is, with specific antibody or specifically sensitized T lymphocytes, or both. Autoimmunity. A condition characterized by a specific humoral or cell-mediated immune response against constituents of the body's own tissues (self-antigens or autoantigens). Autosome. Any chromosome other than a sex chromosome. Humans have 22 pairs of auto- somes. Bioavailability. The fraction of the dose that is absorbed and that reaches the systemic circulation unaltered by biotransformation. Biotransformation. The enzymatic conversion of a compound, usually to a more water- soluble compound. Body mass index. One of the anthropometric measures of body mass. Cell. The basic unit of any living organism. It is a small, watery compartment filled with chemicals and a complete copy of the organism's genome. Sources for the definitions, in addition to members of the committee, include Dorland's Illustrated Medical Dictionary (Philadelphia: W.B. Saunders Co., 2000), The On-line Medi- cal Dictionary (http://www.graylab.ac.uk/~; and Glossary of Genetic Terms developed by National Human Genome Research Institute (http://www.nhgri.nih.gov). 239
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240 EXPLORING THE BIOLOGICAL CONTRIBUTIONS TO HUMAN HEALTH Chromosome. One of the threadlike "packages" of genes and other DNA in the nucleus of a cell. Humans have 23 pairs of chromosomes, 46 in all: 44 autosomes and 2 sex chromo- somes. Each parent contributes one chromosome to each pair, so children get half of their chromosomes from their mothers and half from their fathers. Cytology. The study of cells, their origin, structure, function, and pathology. Diploid. The number of chromosomes in most cells except the gametes (reproductive cells). In humans, the diploid number is 46. Disease. Any deviation from or interruption of the normal structure or function of a part, organ, or system of the body as manifested by characteristic symptoms and signs; the etiology, pathology, and prognosis may be known or unknown. DNA (deoxyribonucleic acid). The chemical inside the nucleus of a cell that carries the genetic instructions required to make living organisms. Dose-response. The relationship between the dose of a drug and the magnitude or inten- sity of the response. Enantiomer. One of a pair of compounds having a mirror-image relationship. Epigenetic mosaic. Occurs when different cells of the same type within an individual have different "gene expression states," e.g., the two types of cells found in all females, those in which their paternal X chromosome is active and those in which their mater- nal X chromosome is active. Exon. The region of a gene that contains the code required to produce the gene's protein. Each exon codes for a specific portion of the complete protein. In some species (includ- ing humans), a gene's exons are separated by long regions of DNA (called introns or sometimes "junk DNA") that have no apparent function. Female. An individual organism of the sex that bears young or that produces ova or eggs. Gametogenic cells. Producing or favoring the production of germ cells. Gender. A person's self-representation as male or female or how that person is responded to by social institutions on the basis of the individual's gender presentation. Gender is shaped by environment and experience (see discussion in Chapter 1~. Gene. The functional and physical unit of heredity passed from parent to offspring. Genes are pieces of DNA, and most genes contain the information required to make a specific protein. Genetics. The study of genes and their heredity. Genome. All the DNA contained in an organism or a cell, which includes both the chromo- somes within the nucleus and the DNA in mitochondria. Genomic imprinting. The concept that some genes are expressed from only the maternal allele and others are expressed from only the paternal allele. Genotype. The genetic identity of an individual that does not show as outward characteris- tics. Germ line. The sequence of cells in the line of direct descent from zygote to gamete, as opposed to somatic cells (all other body cells). Mutations in germ-line cells are trans- mitted to progeny; those in somatic cells are not. Haploid. The number of chromosomes in a sperm or egg cell, half the diploid number. In humans, the haploid number is 23. Haplotype. 1. A set of alleles of a group of closely linked genes, such as the human leuko- cyte antigen complex, which is usually inherited as a unit. 2. The genetic constitution of an individual at a set of closely linked genes on a given chromosome. Hemizygous. Possessing only one instead of a pair of genes of a particular kind.
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APPENDIX C 241 Heterochromatic. Describes the appearance of certain portions of the genome under a light microscope; usually associated with relatively large portions of the genome in which genes that code for products have been silenced or are absent, such as the inactive X chromosome in females or large amounts of simple sequence repeats associated with centromeres. Heterozygous. Possessing two different forms of a particular gene, one inherited from each parent. Homology. The quality of being homologous; the morphological identity of corresponding parts; structural similarity due to descent from a common form. Homozygous. Possessing two identical forms of a particular gene, one inherited from each parent. Hormone. A chemical substance that is produced in the body by an organ, cells of an organ, or scattered cells and that has a specific regulatory effect on the activity of an organ or organs. The term was originally applied to substances secreted by endocrine glands and transported in the bloodstream to distant target organs, but later was applied to various substances having similar actions but not produced by special glands. Immunity. The protection against infectious disease conferred by either the immune re- sponse generated by immunization or previous infection or vaccination (active immu- nity) or transfer of antibody or lymphocytes from an immune donor (passive immu- nity). Infectious disease. A disease caused by a pathogenic microorganism; the etiologic agent may be a bacterium, virus, fungus, or animal parasite and may be transmitted from another host or arise from the host's own indigenous microflora. Innate immunity. Phagocytic cells that respond to toxic signals with no memory capacity (old term: inflammation). In vitro. Within a glass; observable in a test tube; in an artificial environment. In viva. Within the living body. Locus. The place on a chromosome where a specific gene is located, a kind of address for the gene. The plural is "loci." Male. An organism of the sex that begets young or that produces spermatozoa. Meiosis. A special method of cell division, occurring in maturation of the sex cells, by means of which each daughter nucleus receives half the number of chromosomes characteristic of the somatic cells of the species. Meiotic prophase. The stage of meiosis during which DNA replication, homologous pair- ing, and recombination (the exchange of portions of maternal and paternal chromo- somes, such that children receive portions of both grandparents' chromosomes) occur. Mitosis. A method of indirect division of a cell, consisting of a complex of various pro- cesses, by means of which the two daughter nuclei normally receive identical comple- ments of the number of chromosomes characteristic of the somatic cells of the species. Mitosis, the process by which the body grows and replaces cells, is divided into four phases. (1) Prophase: condensation of replicated chromosomes, disappearance of nuclear membrane, appearance of the achromatic spindle, formation of polar bodies. (2) Metaphase: arrangement of chromosomes in the equatorial plane of the central spindle to form the monaster. Chromosomes separate into exactly similar halves. (3) Anaphase: the two groups of daughter chromosomes separate and move along the fibers of the central spindle, each toward one of the asters, forming the diaster. (4) Telophase: the daughter chromosomes resolve themselves into a reticulum and the daughter nuclei are formed; the cytoplasm then divides, forming two complete daugh- ter cells.
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242 EXPLORING THE BIOLOGICAL CONTRIBUTIONS TO HUMAN HEALTH Model (e.g., "animal model"). Any condition found in an animal that is of value in study- ing a biological phenomenon, e.g., a pathological mechanism of an animal disorder useful in studying human disease. Mosaicism. The occurrence in an individual of two or more cell populations, derived from a single zygote, with different chromosomal constitutions. Nondisjunction. Improper separation of chromosomes at nuclear division. Pharmacodynamics. The study of the biochemical and physiological effects of drugs and the mechanisms of their actions, including the correlation of actions and effects of drugs with their chemical structure; also, such effects on the actions of a particular drug or drugs. Contrast with pharmacokinetics. Pharmacology. The medical science that deals with the discovery, chemistry, effects, uses, and manufacture of drugs. Pharmacokinetics. The action of drugs in the body over a period of time, including the processes of absorption, distribution, localization in tissues, biotransformation, and excretion. Phenotype. The total characteristics displayed by an organism under a particular set of environmental factors, regardless of the actual genotype of the organism. Results from interaction between the genotype and the environment. pKoc. The negative logarithm of the ionization constant of an acid (Ka); the buffering power of a buffer system is greatest when its pKa equals the pH. Racemic. Made up of two enantiomorphic isomers and therefore optically inactive. Sex. The classification of living things, generally as male or female, according to their repro- ductive organs and functions assigned by chromosomal complement (see discussion in Chapter 1~. Sexual dimorphism. Having two different distinct forms of individuals within the same species or two different distinct forms of parts within the same organism. For plants, it could refer to different leaf types, flowers, etc. For animals, it could refer to different coloring, sizes, features, etc. Sexual dimorphism is a common case, in which the two sexes have different shapes, sizes, etc. from each other. Stochastic effect. Refers to an event that may occur with a known frequency but for which the outcome of any particular event may not be predicted in advance, such as the flip of a coin (which will be a tail 50 percent of the time). Somatic cells. Usually any cell of a multicellular organism that will not contribute to the production of gametes, i.e., most cells of which an organism is made; not a germ cell. Spermatogenesis. The process of formation of spermatozoa, including spermatocytogenesis and spermiogenesis. Therapeutic index. Relationship between the desired and undesired effecters) of a drug, that is, the benefit/risk ratio. X chromosome. A sex chromosome. In mammals paired in females (XX), in amphibia paired in males. Y chromosome. The small chromosome that is male determining in most mammal species and that is found only in the heterogametic sex. Thus, in mammals the male has one Y chromosome and one X chromosome. Zygote. A single diploid cell resulting from the fusion of male and female gametes (sperm and ovum) at fertilization.