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Unformatted text preview: Chapter 21 Genomes and Their Evolution Reading the Leaves from the Tree of Life • Complete genome sequences exist for a human, chimpanzee, E. coli , brewer’s yeast, nematode, fruit fly, house mouse, rhesus macaque, and other organisms • Comparisons of genomes among organisms provide information about the evolutionary history of genes and taxonomic groups • Genomics is the study of whole sets of genes and their interactions • Bioinformatics is the application of computational methods to the storage and analysis of biological data Scientists use bioinformatics to analyze genomes and their functions • The Human Genome Project established databases and refined analytical software to make data available on the Internet • This has accelerated progress in DNA sequence analysis Identifying Protein-Coding Genes Within DNA Sequences • Computer analysis of genome sequences helps identify sequences likely to encode proteins • Comparison of sequences of “new” genes with those of known genes in other species may help identify new genes Understanding Genes and Their Products at the Systems Level • Proteomics is the systematic study of all proteins encoded by a genome • Proteins, not genes, carry out most of the activities of the cell Genomes vary in size, number of genes, and gene density • By summer 2007, genomes had been sequenced for 500 bacteria, 45 archaea, and 65 eukaryotes including vertebrates, invertebrates, and plants Genome Size • Genomes of most bacteria and archaea range from 1 to 6 million base pairs (Mb); genomes of eukaryotes are usually larger • Most plants and animals have genomes greater than 100 Mb; humans have 3,200 Mb • Within each domain there is no systematic relationship between genome size and phenotype Table 21-1 Number of Genes • Free-living bacteria and archaea have 1,500 to 7,500 genes • Unicellular fungi have from about 5,000 genes and multicellular eukaryotes from 40,000 genes • Number of genes is not correlated to genome size • For example, it is estimated that the nematode C. elegans has 100 Mb and 20,000 genes, while humans have 3,200 Mb and 20,488 genes • Vertebrate genomes can produce more than one polypeptide per gene because of alternative splicing of RNA transcripts Gene Density and Noncoding DNA • Humans and other mammals have the lowest gene density, or number of genes, in a given length of DNA • Multicellular eukaryotes have many introns within genes and noncoding DNA between genes Multicellular eukaryotes have much noncoding DNA and many multigene families • The bulk of most eukaryotic genomes consists of noncoding DNA sequences, often described in the past as “junk DNA” • Much evidence indicates that noncoding DNA plays important roles in the cell • For example, genomes of humans, rats, and mice show high sequence conservation for about 500 noncoding regions • Sequencing of the human genome reveals that 98.5% does not code for proteins, rRNAs, or tRNAs • About 24% of the human genome codes for introns and gene-related regulatory...
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This document was uploaded on 01/23/2012.
- Spring '09