![]() 2001) and it is now a standard component of the analysis of every new genome sequence. Indeed, much of the functional parts of the human genome have been discovered or verified by this type of sequence comparison (Lander et al. Using such computer-based analysis to zero in on the genomic features that have been preserved in multiple organisms over millions of years, researchers are able to locate the signals that represent the location of genes, as well as sequences that may regulate gene expression. In contrast, the chicken and zebrafish alignments with human only show similarity to sequences in the coding exons the rest of the sequence has diverged to a point where it can no longer be reliably aligned with the human DNA sequence. Notice the high degree of sequence similarity between human and macaque (two primates) in both PKLR exons (blue) as well as introns (red) and untranslated regions (light blue) of the gene. Regions of high DNA sequence similarity with human across a 12-kilobase region of the PKLR gene are plotted for each organism. An example of such an alignment is shown in Figure 2, where a human gene (pyruvate kinase: PKLR) and the corresponding PKLR homologs from macaque, dog, mouse, chicken, and zebrafish are aligned. Results such as these provide an extraordinary glimpse into the chromosomal changes that have shaped the mouse and human genomes since their divergence from a common ancestor 75–80 million years ago.Ĭomparison of discrete segments of genomes is also possible by aligning homologous DNA from different species. Other chromosomes, however, show evidence of more extensive interchromosomal rearrangement. Human chromosome 17 corresponds entirely to a portion of mouse chromosome 11. Human chromosome 20 corresponds entirely to a portion of mouse chromosome 2, with nearly perfect conservation of order along almost the entire length, disrupted only by a small central segment. For example, the X chromosomes are represented as single, reciprocal syntenic blocks. ![]() The nature and extent of conservation of synteny differs substantially among chromosomes. Synteny is a situation in which genes are arranged in similar blocks in different species. Figure 1 depicts a chromosome-level comparison of the human and mouse genomes that shows the level of synteny between these two mammals. 2010 see here) and this number continues to grow at a prodigious rate, providing a rich source of genomic data for comparison.įiner-resolution comparisons are possible by direct DNA sequence comparisons between species. Together with over 1,000 prokaryote genomes, a total of over 1,300 species have been completely sequenced and published (ca. 2007) (to name just a few) have also been established. 2006) and rhesus macaque monkey (Gibbs et al. Since the completion of the HGP, sequence drafts of the chicken (Blattner et al. 1996), and the bacterium Escherichia coli (Blattner et al. ![]() 2001), researchers involved in the International Human Genome Project (HGP) sequenced the genomes of a number of important model organisms. In addition to sequencing the three billion letters in the human “genetic instruction book” (Lander et al.
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