Midterm1_2 - Insights from Molecular Systematics Molecular...

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Insights from Molecular Systematics - Molecular trees span both short and long periods of time because molecules evolve at different rates - Conserved sequences like rRNA resolve deep divergences - Rapidly evolving sequences like mtDNA resolve more recent divergence - Molecular phylogenies rely on two types of homologus genes 1. Orthologous 2. Paralogous Duplicate genes have multiple functions -Gene number does not predict complexity i.e Rice: 40,000-50,000 Humans: 20,000-25,000 Pufferfish: 21,000 Nematode: 20,000 Molecular Clock : - The molecular clock is a yardstick for measuring absolute time of evolutionary changed based on the observation that some genes and other regions of genomes appear to evolve at constant rates Neutral Theory - Neutral theory states that much evolutionary change in genes and proteins has no effect on fitness and therefore is not influenced by Darwinian selection - It states that the rate of molecular change in these genes and proteins should be regular like a clock - Architect of neutral theory is Motoo Kimura A B C D A B C C 1 D A B C D Ancestral species Species 1 Species 2 Orthologous (Used to build species trees) Paralogous (Used to reconstruct gene family expansions)
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- Example: Rate of hemoglobin evolution—linear function for amino acid differences vs. time Criticism of Molecular Clocks - Are imprecise - Clock rates vary among genes and among species - Clock rates need to be calibrated with independent data Practical applications of phylogenetics 1. Dating the origin of HIV: phylogeny provides clues about where HIV came from and approximately when it colonized humans 2. HIV infections in Libyan hospital. 400 children infected, 50 died. Six foreign medics
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Midterm1_2 - Insights from Molecular Systematics Molecular...

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