44200 20 Chapter 12 • Genomics 44200 GRIFFITHS FREEM Ch-12 First Pages Sen 12-10-2003 p 20 Application File BLAST searches are used in many other ways, but always the theme is to find out more about some se-quence of interest that the experimenter has identified. PREDICTIONS BASED ON CODON BIAS Recall from Chapter 9 that the triplet code for amino acids is degen-erate; that is, most amino acids are encoded by two or more codons (see Figure 9-8). The multiple codons for a single amino acid are termed synonymous codons. In a given species, not all synonymous codons for an amino acid are used with equal frequency. Rather, certain codons are present much more frequently in the ORFs. For example, in Drosophila melanogaster, of the two codons for cysteine, UGC is used 73 percent of the time, whereas UGU is used 27 percent. This usage is a diag-nostic for Drosophila because, in other organisms, this “codon bias” pattern is quite different. Codon biases are thought to be due to the relative abundance of the
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.