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Phylogeny and the Tree of Life — Slide-by-Slide Lecture Script
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- 系系系系系系系系系系——系系系系系系系系系系系系系系系系系系系系系系系系 系 1 系 系系系 | Phylogeny and the Tree of Life (Ch.26) 系系系系 课课课课课课 26 课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Today we tackle a deceptively simple question: how is every living thing on Earth connected? 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 This chapter is called Phylogeny and the Tree of Life. In plain terms: we're drawing a family tree for all life. 系系系系系 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 系 2 系 系系系系系系系系系 | Overview — Investigating the Tree of Life 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Several lizard groups independently lost their legs. They look snake-like, but they aren't close relatives. 系系系系系系系系系系系系系系系系系系系系系系系系 This plants the central tension of the chapter: looking alike does not mean being related. 系系系 系系系系系系系系系系系系系系系系系系系系系系?系系系系系系系系系系系系系系系系 系 3 系 系 26.1系系系系系系 | Figure 26. 系系系系 课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Use this opener as a mood-setter. Just let the diversity land visually. 系 4 系 系系系系系系系系 | Phylogeny & Systematics defined 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系phylogeny系系系系系系系系系系系系系系系系系——系系系系系系 Phylogeny is the evolutionary history of a species or group — where it came from. 系系系系systematics系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Systematics does two jobs: classify organisms and figure out how they're related. 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Evidence comes from fossils, molecules, and genes. Note we infer relationships — we don't witness them.
系系系系系系 系系系系 infer系系系系系系系系系系系系系系系系系系系系 系 5-8 系 系 26.2 系系系系系系系系系 | Figure 26.2 a–c 系系系系 课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 These images all make one point: unrelated organisms can look alike because they live similar lives. 系系系系系系系系系系系系系系系系系系系系系系系系 Hold onto the phenomenon; we'll name it (convergent evolution) properly later. 系 9 系 系系 26.1 系 系系系 | Concept 26.1 — Phylogenies show relationships; Taxonomy 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系 First big idea: phylogenetic trees display evolutionary relationships. 系系系系系系系系系系系系系系系系系系——系系系系系系系taxonomy系系 To build trees, we first need to name and sort organisms — that's taxonomy. 系 10 系 系系系系系系系系系 | Binomial Nomenclature 系系系系 课课课课课课课课课课课课课课课课课课课课课 18 系系系系系系Linnaeus系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 In the 1700s Linnaeus built a naming system. Two parts survive today: two-part names and a nested hierarchy. 系系系系 系系系系系系系系系系系系系系系系——系系系系系系系系系系系系系系系系系系系系 系 11 系 系系系系系 | How a scientific name works 系系系系 课课课课课课课课课课课课课课课课课课课课课课Homo sapiens课 系系系系系系系系系系系系genus系系系系系系系系系系系系系系系系系系系系系系系系系 A name has two parts: the genus (capitalized) plus the specific epithet, all italicized. 系系系系系系系系系系系系系系系系系系系系系系系系系系 Homo sapiens系 Important: the epithet alone is not the species — you need both words, e.g., Homo sapiens. 系系系系系 系系系 Homo sapiens系系系系系系系系系系系系系系系系系系系系系 系 12 系 系系系系 | Hierarchical Classification 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课taxon课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系taxon系系 From broad to narrow: domain, kingdom, phylum, class, order, family, genus, species. Any one group at any level is a taxon. 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 But beware: the same rank isn't comparable across lineages. An order of snails holds far less diversity than an order of mammals. 系系系系 系系系系系系系系系/系系系系系系系系系系系系系系系系系系系
An early-diverging branch is a basal taxon. If three or more lineages burst from one point unresolved, that's a polytomy. 系系系系系 polytomy 系系系系系系系系系系系系系系系系系系系系系系系系系系 系 19 系 系 26.5 系系系系系 | Figure 26.5 — Anatomy of a tree 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课课A–G 课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 This figure labels every term on one tree. Have students physically point: which is the root, the sisters, the polytomy. 系系系 系系系系系系系系系系系系系系系系系系系系系?系系系系系系系系 系 20 系 系系系系系系系系 | What trees do NOT tell you 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 This slide is exam gold. A tree shows branching order only — not how alike things look, not how much time passed, not how much change occurred. 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 The classic mistake: thinking the taxon next to you is your ancestor. It isn't — it's your cousin. 系系系 系系系系系系系系系系系系系系系系系系系系系系系系系系系 系 21 系 系系系系系系系 | Applying Phylogenies 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Phylogeny solves cases. Researchers once used it to ID which whale species mystery 'whale meat' came from. 系系系系 系系系系系系系系系——DNA系系系系系系系系系系 系 22 系 系 26.6 系系系系系系 | Figure 26.6 — Whale meat results 系系系系 课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Each unknown sample drops neatly onto a known whale branch. That placement is the evidence. 系 23 系 系系 26.2 | Concept 26.2 — Data behind phylogenies 系系系系 课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系——系系系系系系系系系系系系系系系系系系系系系系 Second big idea: we build trees from two data types — visible morphology and invisible molecules (genes, biochemistry). 系 24 系 系系系 | Homologies 系系系系 课课课课课课课课课课课课课课课课课 DNA 课课课课课课课课课课 系系系系系系系系系系系系系系homology系系系系系系系 DNA 系系系系系系系系系系系系系系 Similarity inherited from a shared ancestor is homology. Similar form or DNA usually signals closer kinship.
The key word is usually — because there's an exception, revealed next. 系 25 系 系系 vs 系系 | Homology vs Analogy 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系analogy系系系 The big trap when building trees: tell homology apart from analogy. 系系系系系系系系系系系系系系系系系系系——系系系系系系系系系系系 Homology comes from shared ancestry; analogy comes from convergent evolution — independent and coincidentally alike. 系系系系系 系系系 2 系系系系系系——系系系系系系系系系系系 系 26 系 系系系系 | Convergent Evolution 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Convergent evolution: separate lineages face similar pressures and selection pushes them toward similar solutions. 系系系系 系系系系系系系系系系系系系系系系系系系系系系系系系系系系 系 27 系 系 26.7 系系系系系 | Figure 26. 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 This side-by-side is the textbook analogy: barely related, yet near-twins. 系 28 系 系系系系系系系系系 | Telling homology from analogy 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课课homoplasy课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Bat and bird wings are clever: homologous as forelimbs, analogous as wings. Same structures, two identities. 系系系系系系系系系系系系系系homoplasy系系系系系系系系系系系系系系系系系系系系系系系系系系系 Independently evolved similarity is also called homoplasy. Rule of thumb: the more complex the shared detail, the likelier it's true homology. 系系系 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系——系系系系系系系 系 29 系 系系系系系系 | Evaluating Molecular Homologies 系系系系 课课课课课课课课课课课课课课课课课课课课 DNA 课课课 系系系系系系系DNA 系系系系系系系系系系系系系系系系系系系系系系系系 At the molecular level DNA is long, so we use computers and math to align comparable segments across species. 系 30-33 系 系 26.8 系系 系系系系 | Figure 26.8 (1–4) — Sequence alignment 系系系系 课课课课课课课课/课课课课课课课课课课课课课课 系系系系系系系系系系系系 DNA 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系
Start with monophyletic (a): enclose one ancestor and all its descendants — clean. 系系系 系系系系 A–G 系系系系系系系系系系系系系系系系系系系系系 系 41-42 系 系系系 系 系 26.10b | Paraphyletic + Fig 26.10b 系系系系 课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Paraphyletic: you've got the ancestor but left out some descendants. 'Reptiles' excluding birds is the classic case. 系系系系 系系系系系系系系系系系系系系系系系系系——系系系系系系系系系系 系 43-44 系 系系系 系 系 26.10c | Polyphyletic + Fig 26.10c 系系系系 课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Polyphyletic is the worst grouping: members have different ancestors. Like lumping all 'flying animals' together. 系系系系系系系系系系系系系系系系系系系系 Ranking to remember: monophyletic best, paraphyletic so-so, polyphyletic worst. 系 45 系 系系系系 vs 系系系系 | Ancestral vs Derived characters 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Compared to its ancestor, an organism carries some inherited traits and some new ones. 系 46 系 系系系系系系 | Shared ancestral vs shared derived 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Shared ancestral character: an old trait from the ancestor. Shared derived character: a novelty unique to one clade. 系系系系系系系系系系系系系系系系系系系系系系系——系系系系系系系系系系系系 Neat twist: the same trait flips identity depending on comparison level — derived here, ancestral there. 系系系 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 系 47 系 系系系系系系系 | Inferring trees using derived characters 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 The trick to building trees: locate where each new trait first appears — that's the dividing line. 系 48-50 系 系 26.11 系系 系系系系系系 | Fig 26.11 — Vertebrate worked example 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系 0/1 系系系系系系系系系系系系系系系系系系系系系 This is the chapter's key worked example. The 0/1 table records which traits each animal has; the tree is built from it. 系系系系系系系系 1 系系系系系系系系系系系系系系系系系系系系系系 1 系系系系系系系系
Reading it: each additional '1' crosses another trait threshold on the tree. The leopard has all 1s, so it sits at the tip. 系系系系 系系系系系系系系系——系系系系系系系系系系系系系 0/1 系系系系 系 51 系 系系系 | Outgroup 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系outgroup系系系系系系系系系系系系系系系系系系系系系系系系系系系 An outgroup is a relative of the group you're studying (the ingroup) that branched off earlier. 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 It acts like a control: comparing each ingroup member to it sorts old traits from new. 系系系 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 系 52 系 系系系系系系 | Why the outgroup works 系系系系 课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 The logic is simple: if the outgroup has the trait too, it predates the split — it's ancestral. 系 53 系 系系系系系系系系 | Branch length = genetic change 系系系系 课课课课课课课课课课课课课课 DNA 课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系 DNA 系系系系系 In one kind of tree, branch length matters: longer means more DNA change along that lineage. 系 54 系 系 26.12 系系系系 | Fig 26. 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系——系系系系系系系系系系系系系系系系系系 Notice unequal branches: you can see which lineage changed most. But remember — this measures amount of change, not time. 系 55 系 系系系系系 | Branch length = time 系系系系 课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 The other kind flips it: branch length represents time, with split dates pinned by the fossil record. 系系系系系 系系系系系系系系系系系系系系系系系系系系系系系系系系系 系 56 系 系 26.13 系系系 | Fig 26.13 — Time-scaled tree 系系系系 课课课课课课课课课课课课课课课课课课/课课课/课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Same animals, now with a time axis in millions of years. Compare to the last figure to feel the difference. 系 57 系 系系系系系系系系系 | Maximum Parsimony & Likelihood 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课
系系系 系系系系系系系系系系系系系系?系系系系系系系系系系 系 68 系 系 26.16 系系系系 | Fig 26.16 — Archosaur tree 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 On this tree, dinosaurs are bracketed between crocodiles and birds. Traits shared by both flanks, dinosaurs likely had too. 系 69 系 系系系系系系 | Bracketing dinosaurs 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Birds and crocodiles both have four-chambered hearts, vocalize, build nests, and brood. Bracketed dinosaurs probably did as well. 系系系系系系系系系系系系系系系——系系系系系系系 And fossils actually confirm nesting and brooding in dinosaurs — the prediction held up. 系系系系系 系系系系系—系系系系系系系系系系系系系系系系系系系系 系 70 系 系系系系系系系 | Animation — The Geologic Record 系系系系 课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 There's a geologic-record animation here (right-click to play). If short on time, skip it and just note that strata act as a time ruler. 系 71-73 系 系 26.17 系系 系系系系系 | Fig 26.17 — Oviraptor & eggs 系系系系 课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Here's the smoking gun: an Oviraptor fossil sitting on its own eggs, brooding. The reconstruction recreates the posture. 系系系系系系系系系系系系系系系系系系系系系系系系系系 A fun correction: 'Oviraptor' means egg-thief, but it was actually guarding its own eggs, not stealing. 系系系 系系系系系系系系系系系系系系系系系系系系系系系系 系 74 系 系系 26.4 | Concept 26.4 — History in the genome 系系系系 课课课课课rRNA 课课课课课课课课课课mtDNA 课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系 Fourth big idea: evolutionary history is recorded in the genome; comparing molecules traces kinship. 系系系系系系系系系rRNA 系系系系系系系系系系系系系系系系mtDNA 系系系系系系系系系系系系系系 Choice of molecule matters: rRNA changes slowly — good for ancient splits; mtDNA changes fast — good for recent events. 系系系 rRNA 系系系系mtDNA 系系系——系系系系系系系系系系系系
系 75 系 系系系系系系系系系 | Gene Duplication & Families 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Genes sometimes get duplicated. The spare copy is evolution's scratch paper — free to mutate and try new functions. 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Repeated duplication builds gene families, which also trace back to a common ancestral gene. 系 76 系 系系系系系系 | Orthologous genes 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系orthologs系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Orthologs: the same gene separated by speciation, usually one copy per species. 系系系系系系系系系系系系系系系系系 They diverge only after the species split. 系 77-78 系 系 26.18 系 a 系系/系系 | Fig 26.18 (+a) — Ortho vs Para 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系→系系系系系系系系系系系系系系系→系系系系系 This figure nails both terms: species split → orthologs; gene duplicates within one species → paralogs. 系系系系系系a系系系系系系系系系系系系系系系系系系系系系系系系系系系 Start with the left half (a): one ancestral gene splits with the species into orthologs in two species. 系系系系 ortho系系系系系系系系系系系para系系系系系系系系系系系系系 系 79-80 系 系系系系系系 系 系 26.18b | Paralogs + Fig 26.18b 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系paralogs系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Paralogs come from gene duplication, so several copies sit in one genome, often evolving new jobs. 系系系 系系系系系系系系系系系系系系系系系——系系系系系系系系系系系系 系 81 系 系系系系系系系系 | Genome Evolution I 系系系系 课课课课课课课课课课课课课课 6500 课课课课课课99% 课课课课课课课课 系系系系系系系系系系系系系系系系系系系系 6500 系系系系系系系 99% 系系系系系系系系系系 Orthologs are everywhere. Stunning stat: humans and mice split 65 million years ago, yet 99% of our genes are still orthologous. 系系系系系 系 99% 系系系系系系系系系系系系系系系系系系系系系系系 系 82 系 系系系系系系系系 | Genome Evolution II 系系系系 课课课课课课课课课课课课课课课课课课课课课课 4 课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 4 系系 Counterintuitive: gene count and complexity aren't tightly linked. Humans have only about four times as many genes as yeast.
In reality the clock isn't perfectly smooth. Selection favors some changes, speeding or slowing the tick. 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Estimates far beyond the fossil record carry big uncertainty. The fix: average over many genes to cancel noise. 系系系系系 系系系系系系系系系系系系系系系系系系系系系系系系系系 系 89 系 系系系HIV 系系 | Application — Origin of HIV 系系系系 HIV 课课课课课课课课课课课课课课课课课课课课课课课课课课 1930 课课课课课 系系系系系系系系系系 HIV 系系系系系系 HIV 系系系系系系系系系系系系系系系系系系系系系系系系系系 A real-world case: the clock applied to HIV. Analysis shows HIV descends from primate viruses and jumped to humans more than once. 系系系系系系系系系系系系系系系系系系系系系系系 1930 系系系系系系系系系系 Because it evolves so regularly, the clock dates one strain's jump into humans to roughly the 1930s. 系系系系系 系系系系系系系系系系系系系系系系系系系系系系系系系系 系 90 系 系 26.20 HIV 系系系系 | Fig 26.20 — Dating HIV 系系系系 课课课课课课课 HIV 课课课课课课课课课课课课课课课课 1930s课 系系系系系系系系系系系系系系系 HIV 系系系系系系系系系系系系系系系系系 1930 系系系系系 Follow the fitted line: plotting sequence differences against sample year and extrapolating backward lands near the 1930s. 系 91 系 系系 26.6 | Concept 26.6 — Revising the tree 系系系系 课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Final big idea: the tree of life isn't finished; molecular systematics keeps rewriting its deepest branches. 系 92 系 系系系系系系 | Two Kingdoms to Three Domains 系系系系 课课课课课课课课→课课→课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系/系系系系系系系系系系系系系系系系系系系——系系系系系系系系系 The history reads like upgrades: first two kingdoms (plant/animal), then five kingdoms, now three domains — Bacteria, Archaea, Eukarya. 系系系系系系系系系系系系系系系系系系系系系 The three-domain system is backed by many sequenced genomes — solid evidence. 系系系 系系系系系系系系系系——系系系系系系系系系系 系 93 系 系系系系系系系 | Animation — Classification Schemes 系系系系 课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系→系系→系系系系 Another playable animation here, showing how classification schemes shifted. Play it if time allows to visualize two-to-five-to-three.
系 94-97 系 系 26.21 系系 系系系系 | Fig 26.21 — Tree of three domains 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 This is the chapter's group photo: Bacteria, Archaea, Eukarya, all sprouting from a common ancestor. 系系系系系系系系系系系系系系系——系系系系系系系系系系系系系系系系系系系系系系系 Note the bracketed mitochondria and plastids — they came from engulfed bacteria, a nod to endosymbiosis. 系系系 系系系a/b/c系系系系系系系系系系系系系系系系系系系系 系 98 系 系系系系系系系 | A simple tree of all life 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课 rRNA 课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 A surprising conclusion: eukaryotes (including us) are more closely related to archaea than to bacteria. 系系系系系系系系系系系 rRNA 系系系系系系系系系系系系系系系系 This tree rests largely on slow-changing rRNA genes, which is why it reaches so deep. 系 99 系 系系系系系系 | Horizontal Gene Transfer 系系系系 课课课课课课课课课课课HGT课课课课课课课课课课课课课课课课课课课课课/课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系HGT系——系系系系系系系系系系系系系系系系系系系系系系系系系系系 There's a plot twist: horizontal gene transfer — genes don't only pass down to offspring, they can leap sideways between organisms. 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 Routes include plasmids, viruses, even cell fusion. The result: the tree's base is tangled, not tidy. 系系系系系 系系系系系系系系系系系系系系系系系系系系系系系系?系系系系系系系 系 100 系 系 26.22 系系系系系 | Fig 26.22 — Tangled base 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系——系系系系系系系系系系系系系系系系系系系系 See those horizontal links near the root — traces of gene swapping between domains billions of years ago. 系 101 系 系系系系系系系系系系系 | Tree or Ring of Life? 系系系系 课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 A bold hypothesis: eukaryotes may have arisen by fusion of a bacterium and an archaean. If so, a ring of life may fit early history better than a tree. 系系系系系 系系系系系系——系系系系系系系系系系系系系系系系系系系系系系系 系 102 系 系 26.23 系系系系 | Fig 26.23 — Ring of Life 系系系系 课课课课课课课课课课课课课课课课课课课课课 系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系系 This Ring of Life joins the three domains in a circle, with eukaryotes at the bacterium-archaean fusion. Leave students with: a tree may not be the only shape.
