Evolution__3rd_Edition

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Evolutionary genomics aims to
answer questions about the
evolution of genomes
CHAPTER 19 / Evolutionary Genomics 557
19.1 Our expanding knowledge of genome sequences is
making it possible to ask, and answer, questions about
the evolution of genomes
Advances in any area of biology usually lead, in time, to a deeper understanding of
evolution. From the 1960s to the 1990s, techniques to work out the amino acid
sequences of proteins and the nucleotide sequence of genes were devised, perfected,
and then industrialized. The resulting gush of data has allowed biologists to look again
at the tree of life, as we have seen in Chapters 15 and 18. (It also led to the neutral theory
of molecular evolution, as we saw in Chapter 7.) This chapter and the next will look at
two new areas of evolutionary biology that have grown up along with advances in
molecular genetics. In this chapter, we look at evolutionary genomics, which has grown
out of whole-genome sequencing. In the next chapter we look at “evo-devo,” which
exploits our ability to identify the individual genes that control development.
The genome of an organism is its complete set of DNA. The genomic sequences,
and partical sequences, of organisms from several species can be used to study how
genomes change during evolution. Evolutionary genomics is concerned with any question
that can be asked about the evolution of genomes. To introduce the subject, here
are some examples of questions that can be asked about genome evolution.
1. How, and why, has the total size of the genomes changed?
2. Why is the DNA of some species longer than in other species?
We can break down the total genome into coding and non-coding parts, and ask
questions such as:
3. Do some species have more coding DNA (that is, more or larger genes) than other
species? And if so, why?
4. Why do some species have more non-coding (and perhaps “junk”) DNA than
others?
5. How do the different parts of genomes change in size during evolution?
The DNA is arranged in chromosomes, and we can ask about chromosome evolution:
6. How does the chromosomal arrangement of genes change during evolution? Do
genes stay on the same chromosomes over evolutionary time, and in the same order,
or do genes move about within and between chromosomes?
We can also try to relate genome evolution to other evolutionary events:
7. When have genomic changes occurred?
8. What genomic changes are associated with major evolutionary events, such as the
origin of animals or the origin of vertebrates? Were these major events produced
by changes in the number of genes, or by changes in the sequences of a constant
number of genes?
Some of these questions could have been asked before the era of DNA sequencing,
but the growth of DNA sequence evidence has stimulated evolutionary genomic
research. The sequence data itself has also enabled many new kinds of tests. Research is
at a preliminary stage, however, because research is limited to genomes that have been
sequenced, or mainly sequenced. That has limited recent research to humans, the mouse
(in part), the worm (Caenorhabditis elegans), the fruitfly (Drosophila melanogaster), and
the weed (Arabidopsis) among multicellular eukaryotes, together with several prokaryotes.