An early graphical method for comparing nucleotides sequences—the so-called diagon plot—still yields one of the best visual comparisons of sequence relatedness. An example is illustrated in Figure Q9–11, in which the human β-globin gene is compared with the human cDNA for β globin (which contains only the coding portion of the gene; Figure Q9–11A) and with the mouse β-globin gene Figure Q9–11B). Diagon plots are generated by comparing blocks of sequence, in this case blocks of 11 nucleotides at a time. If 9 or more of the nucleotides match, a dot is placed on the diagram at the coordinates corresponding to the blocks being compared. A comparison of all possible blocks generates diagrams such as the ones shown in Figure Q9–11, in which sequence similarities show up as diagonal lines.

Figure Q9–11

Transcribed Image Text:

5' human ß-globin DNA 3' (A) HUMAN B-GLOBIN CDNA COMPARED WITH HUMAN B-GLOBIN GENE in human B-globin gene 3' 3' mouse B-globin gene 5' (B) MOUSE B-GLOBIN GENE COMPARED WITH HUMAN B-GLOBIN GENE 5' human B-globin gene 3'