24.1 Evolutionary history is written in genomes.
Comparative Genomics
• An important challenge of modern evolutionary biology is to link the evolution of DNA sequences with the evolution of complex morphological characters used to construct phylogenies. (p. 492)
• Over 100 prokaryotic genomes and at least 18 eukaryotic genomes have either been completed or are currently being sequenced. (pp. 492-494)
• The pufferfish genome has 365 million base-pairs -- basically the same number of genes as the human genome, but only one-ninth of the DNA. (p. 494)
• Humans share 99% of their genes with mice, and thus only diverged about 75 MYA. (p. 494)
• Differences in development are explained by genes being expressed at different times and/or in different tissues. (p. 494)
• Humans and chimps diverged from a common ancestor about 5 MYA, and their sequences are 98.7% identical. (p. 495)
• If only small chromosomal differences exist between distantly related vertebrates over the past 300 million years, a reasonable hypothesis is that the common ancestor had a similar genome. (p. 495)
• The fruit fly (Drosophila) and the mosquito (Anopheles) are separated by about 250 million years of evolution, and appear to have evolved more rapidly during that time than vertebrates did. (p. 496)
Origins of Genomic Differences
• Genomic changes can be made by at least six factors: the mutation of a single gene, duplicated regions of DNA, rearrangements of large chunks of DNA, chromosome duplication, polyploidy, and interspecies gene integration. (p. 497)
• Growing evidence indicates that duplication of just a few genes has been a major contributor to morphological diversity. (p. 497)
• Whole-genome duplication is insufficient to explain the size of some genomes. (p. 497)
• One of the greatest sources of novel genomic traits is the duplication of DNA segments. The fate of the duplicate gene is most likely either the gaining of a novel function or the loss of function through subsequent mutations. (p. 497)
• About 5% of the human genome consists of segmental duplications. (pp. 497-499)
• Genomes also evolve due to the loss of gene function. (p. 499)
• Vertical gene transfer refers to genes passing from generation to generation, while lateral gene transfer refers to genes moving from one species to another. (p. 499)
• Gene swapping appears to have occurred frequently early in the history of life. (pp. 499-500)
• Most human lateral gene transfer appears to have occurred millions of years ago. (p. 500)
24.2 Developmental mechanisms are evolving.
Evolution of Development
• Genes with similar sequences in two different species may work in different ways. (p. 501)
• Regulatory genes may turn on different sets of genes in different organisms. (p. 501)
• About two dozen conserved gene families regulate animal development. (p. 501)
• Changing the timing of gene expression, and/or the genes expressed, can result in dramatic changes in form. (p. 503)
• New functions can arise for existing structures by the recruitment of existing regulatory programs. (p. 503)
• Although gene function can be inferred from sequence data, actual gene function must be exhibited through experimentation. (p. 503)
Diversity of Eyes in the Natural World
• Natural selection can build very complicated structures via incremental improvements in function. (p. 504)
• Eye development in many different animal groups is an example of convergent evolution and represents analogous structures, but a common gene appears to initiate eye development in many of these animals. (p. 504)