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Biology 1001A

Lecture 04: Biodiversity Approximate times by which - First cells had appeared: 3.5 billion years ago - First eukaryotic cells had appeared: 2.5 billion years ago Domain systems for classifying living things - Two-kingdom: plants, animals - Five-kingdom: prokaryotes, protists, fungi, plants, animals - Three-kingdom: eubacteria, archaebacteria, eukaryota Main characteristics distinguishing Eubacteria, Archaea, Eukaryota domains life - Eubacteria: unicellular organisms with circular DNA - Archaea: unicellular organisms that live in extreme conditions (circular DNA) o Different rRNA sequences - Eukaryota: contains both unicellular and multicellular organisms (linear DNA) Meaning of horizontal gene transfer (HGT) - HGT: transfer and incorporation of one organism’s/species DNA into the DNA of a different organism or species - Contrasts dramatically with the vertical transmission of genes from generation to generation (e.g., plasmids or transposons) - Thus makes it challenging to recreate universal tree of life Monophyletic vs. polyphyletic groups of organisms - Monophyletic: one origin - Polyphyletic: many origins Most recent common ancestor (MRCA) for groups, given a phylogenetic tree (Branching points on tree of life) - MCRA of humans estimated to be about 3,000 years ago 1. Chimps and bonobos - hence humans are not descended from chimps - just share a common ancestry – we are cousins! 2. Gorillas; MCRA of African great apes (humans, chimps, bonobos) 3. Orangutans; MCRA of all great apes (evolved in Asia) 4. Gibbons; MCRA of all apes 5./6. Old World and New World monkeys 7. Tarsiers 8./9. Lemurs and lorises; MCRA of all primates (65 million years ago – end: cretaceous mass extinction) 10. Rodents
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