active site The part of a protein that must be maintained in a specific shape if the protein is to be functional, for example, the part to which the substrate binds in an enzyme. The part of an enzyme where the actual enzymatic function is performed adaptation In the evolutionary sense, some heritable feature of an individuals phenotype that improves its chances of survival and reproduction in the existing environment adaptive landscape The surface plotted in a three-dimensional graph; with all possible combinations of allele frequencies for different loci plotted in the plane; and mean fitness for each combination plotted in the third dimension adaptive peak a high point(perhaps one of several)on an adaptive landscape; selection tends to drive the genotype composition of the population toward a combination corresponding to an adaptive surface See adaptive landscape adaptive value See fitness additive genetic variance Genetic variance associated with the average effects of substituting one allele for another additive model A mechanism of quantitative inheritance in which alleles at different loci either add a fixed amount to the phenotype or add nothing adenine A purine base that pairs with thymine in the dNa double helix. See purines adenosine The nucleoside containing adenine as its base adenosine triphosphate See atp adjacent segregation In a reciprocal translocation heterozygote during meiosis the segregation of a translocatedactive site The part of a protein that must be maintained in a specific shape if the protein is to be functional, for example, the part to which the substrate binds in an enzyme. The part of an enzyme where the actual enzymatic function is performed. adaptation In the evolutionary sense, some heritable feature of an individual's phenotype that improves its chances of survival and reproduction in the existing environment. adaptive landscape The surface plotted in a three-dimensional graph; with all possible combinations of allele frequencies for different loci plotted in the plane; and mean fitness for each combination plotted in the third dimension. adaptive peak A high point (perhaps one of several) on an adaptive landscape; selection tends to drive the genotype composition of the population toward a combination corresponding to an adaptive peak. adaptive surface See adaptive landscape. adaptive value See fitness. additive genetic variance Genetic variance associated with the average effects of substituting one allele for another. additive model A mechanism of quantitative inheritance in which alleles at different loci either add a fixed amount to the phenotype or add nothing. adenine A purine base that pairs with thymine in the DNA double helix. See purines. adenosine The nucleoside containing adenine as its base. adenosine triphosphate See ATP. adjacent segregation In a reciprocal translocation heterozygote during meiosis the segregation of a translocated