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adaptation: Any heritable characteristic of an organism that improves its ability to survive and reproduce in its environment. Also used to describe the process of genetic change within a population, as influenced by natural selection.
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adaptive radiation: The diversification, over evolutionary time, of a species or group of species into several different species or subspecies that are typically adapted to different ecological niches (for example, Darwin's finches). The term can also be applied to the evolution of larger groups of organisms, as in "the adaptive radiation of mammals."
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alleles: One of the alternative forms of a gene. For example, if a gene determines the seed color of peas, one allele of that gene may produce green seeds and another allele produce yellow seeds.
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amino acid: The unit molecular building block of proteins, which are chains of amino acids in a certain sequence. There are 20 main amino acids in the proteins of living things, and the properties of a protein depend upon its particular amino acid sequence.
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amino acid sequence: A series of amino acids, the building blocks of proteins, usually coded for by DNA. Exceptions are those coded for by the RNA of certain viruses, such as HIV.
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biodiversity (or biological diversity): A measure of the variety of life, biodiversity is often described on three levels. Ecosystem diversity describes the variety of habitats present; species diversity is a measure of the number of species and the number of individuals of each species present; genetic diversity refers to the number of alleles of the genes within a species.
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biogeography: The study of patterns of geographical distribution of plants and animals across Earth, and the changes in those distributions over time.
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biosphere: The part of Earth and its atmosphere capable of sustaining life.
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