| adaptive | Favored by natural selection in a particular environment.
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| allele | A biochemical variant of a particular gene.
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| Allen’s rule | Rule stating that the relative size of protruding body parts (such as ears, tails, bills, fingers, toes, and limbs) tends to increase in warmer climates.
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| Bergmann’s rule | Rule stating that the smaller of two bodies similar in shape has more surface area per unit of weight and can therefore dissipate heat more efficiently; hence, large bodies tend to be found in colder areas and small bodies in warmer ones.
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| catastrophism | View that extinct species were destroyed by fires, floods, and other catastrophes. After each destructive event, God created again, leading to contemporary species.
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| chromosomes | Basic genetic units, occurring in matching (homologous) pairs; lengths of DNA made up of multiple genes.
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| creationism | Explanation for the origin of species given in Genesis: God created the species during the original six days of Creation.
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| dominant | Allele that masks another allele in a heterozygote.
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| eugenics | Controversial movement aimed at genetic improvement by encouraging the reproduction of individuals with favored features and discouraging that of individuals with features deemed undesirable.
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| evolution | Belief that species arose from others through a long and gradual process of transformation, or descent with modification.
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| gene | Area in a chromosome pair that determines, wholly or partially, a particular biological trait, such as whether one’s blood type is A, B, or O.
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| gene flow | Exchange of genetic material between populations of the same species through direct or indirect interbreeding.
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| gene pool | All the alleles and genotypes within a breeding population—the “pool” of genetic material available.
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| genetic evolution | Change in gene frequency within a breeding population.
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| genotype | An organism’s hereditary makeup.
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| heterozygous | Having dissimilar alleles of a given gene.
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| homozygous | Possessing identical alleles of a particular gene.
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| independent assortment | Mendel’s law of; chromosomes are inherited independently of one another.
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| meiosis | Special process by which sex cells are produced; four cells are produced from one, each with half the genetic material of the original cell.
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| Mendelian genetics | Studies ways in which chromosomes transmit genes across the generations.
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| mitosis | Ordinary cell division; DNA molecules copy themselves, creating two identical cells out of one.
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| mutation | Change in the DNA molecules of which genes and chromosomes are built.
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| natural selection | Originally formulated by Charles Darwin and Alfred Russel Wallace; the process by which nature selects the forms most fit to survive and reproduce in a given environment, such as the tropics.
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| phenotypical adaptation | Adaptive biological changes that occur during the individual’s lifetime, made possible by biological plasticity.
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| population genetics | Field that studies causes of genetic variation, maintenance, and change in breeding populations.
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| random genetic drift | Change in gene frequency that results not from natural selection but from chance; most common in small populations.
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| recessive | Genetic trait masked by a dominant trait.
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| recombination | Following independent assortment of chromosomes, new arrangements of hereditary units produced through bisexual reproduction.
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| sexual selection | Based on differential success in mating, the process in which certain traits of one sex (e.g., color in male birds) are selected because of advantages they confer in winning mates.
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| speciation | Formation of new species; occurs when subgroups of the same species are separated for a sufficient length of time.
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| species | Population whose members can interbreed to produce offspring that can live and reproduce.
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| Thomson’s nose rule | Rule stating that the average nose tends to be longer in areas with lower mean annual temperatures; based on the geographic distribution of nose length among human populations.
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| uniformitarianism | Belief that explanations for past events should be sought in ordinary forces that continue to work today.
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