44200 32 Chapter 12 • Genomics 44200 GRIFFITHS FREEM Ch-12 First Pages Sen 12-10-2003 p 32 Application File 29. You have sequenced the genome of the bacterium Salmonella typhimurium, and you are using BLAST analysis to identify similarities within the S. typhi-murium genome to known proteins. You find a pro-tein that is 100 percent identical in the bacterium Escherichia coli. When you compare nucleotide sequences of the S. typhimurium and E. coli genes, you find that their nucleotide sequences are only 87 percent identical. a. Explain this observation. b. What do these observations tell you about the merits of nucleotide versus protein similarity searches in identifying related genes? C HALLENGING P ROBLEMS 30. From in situ hybridizations, five different YACs con-taining genomic fragments were known to hybridize to one specific chromosome band of the human genome. Rare-cutting restriction enzymes (which have 8-bp recognition sequences and cut on average once in every 64,000 bp) were used to digest genomic DNA. Radioactively labeled YACs were each hybridized to
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