Characterization of populations. Schematic illustration of two populations in terms of distributions of some measurable parameter and in terms of the mean values for those distributions. Similarity-based characterization of these populations focuses on the distributions, whereas identity-based characterization focuses on the means and treats the distribution as noise or as aberrant values.

Amino acids in zinc fingers. A: In large dark rectangle, sequence of amino acids 11 to 276 in transcription factor IIIA of Xenotopus laevis oocytes, aligned in nine rows to show extent of repetition of repeat units. Letters below rectangle indicate consensus sequence derived by Miller, McLachlan, and Klug (1985); dashes in consensus sequence indicate positions of no consensus. Shaded letters highlight acids that match the consensus sequence; letters in small gray rectangles indicate acids that do not match the consensus sequence but match at least one other acid in that position; unshaded letters match neither the consensus sequence nor any other acid. Blanks indicate gaps in the alignment, with the gaps positioned to maximize match of surrounding acids with the consensus sequence. Asterisks do not represent acids but indicate positions at which "insertions" commonly occur. Adapted from Figure 3 of Miller, McLachlan, and Klug (1985). B: Model of the arrangement of amino acids 103 to 204 in transcription factor IIIA of Xenotopus laevis oocytes. Three complete "zinc fingers" are shown. Adapted from Figure 4 of Miller, McLachlan, and Klug (1985). Note that the amino acids that most consistently match the consensus sequence in A are those that serve as ligands with zinc in B.