Evolution, 4th Edition

346 CHAPTER 14

This chapter explores the evolution of the genome by first discussing how new

genes originate. It then discusses the different fates of new genes and looks at how

genes die. The next topic is the evolution of protein-coding genes by changes to

their sequences and their expression. We then consider how and why the number

and structure of chromosomes evolve. Finally, we tackle the evolution of genome

size and genome content, including the puzzle of why so much DNA has no obvi-

ous function.

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10 –1 1 10 102 103 104 105 106

Prokaryotes

All eukaryotes

Algae

Protists

Fungi

Vascular plants

Arthropods

Chordates

Fishes, amphibians

Birds, mammals,

reptiles

Genome size (Mb)

FIGURE 14.1 Genome size variation. The bars

indicate the range of genome size (shown in

megabases, Mb; 1 Mb = 10^6 bases) across spe-

cies within each group. Some protists (which are

unicellular eukaryotes) have genomes that are

hundreds of times larger than that of any mammal.

(After [22, 53].)

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Diatom (Thalassiosira)

Plants

Fungi

Animals

Malaria parasite (Plasmodium)

Red alga (Cyanidioschyzon)

Rice (Oryza)

Mouse-ear cress (Arabidopsis)

Legume (Lotus)

Smut fungus (Ustilago)

Yeast (Schizosaccharomyces)

Bread mold (Neurospora)

Yeast (Saccharomyces)

Nematode (Caenorhabditis)

Mosquito (Anopheles)

Fruit y (Drosophila)

Silk worm (Bombyx)

Tunicate (Ciona)

Puffer sh (Fugu)

Chicken (Gallus)

Mouse (Mus)

Human (Homo)

100 20 30 40 50 60

Number of genes (× 1000)

Common

ancestor

*

*

*

*

*

FIGURE 14.2 Numbers of protein-coding genes for several

eukaryotes, arranged on a phylogeny. Some patterns make

intuitive sense: multicellular eukaryotes with tissue organiza-

tion (plants and animals) have more protein-coding genes than

most unicellular eukaryotes and multicellular eukaryotes without

distinct tissues (indicated by asterisks). Other patterns are puz-

zling: rice has more than twice as many protein-coding genes as

the other flowering plants shown, and puffer fishes have almost

twice as many as humans. (After [60].)

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